Back to Earth | Sustainable Building Materials

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We’ve developed the first free, online wood fibre insulation course. Designed for architects, builders and self-builders, the course covers how to specify, source and use wood fibre effectively.

If you’re working on a building project and need help specifying your materials, checkout the following.

Internal insulation is essentially insulation which is applied to the inner face of external walls in a building. 

It’s usually bonded or screwed to the walls and usually extends from the very bottom of the ground floor all the way up to the eaves level and then carries on and meets up with the roof insulation. 

It’s there to provide a full internal skin of insulation to keep the interior of the building warm.

It’s applied to the walls.  It’s there to prevent heat loss through the walls, but the really important thing about internal insulation is that it provides a barrier between you and the masonry wall beneath. 

This is an important point because it’s something that external insulation doesn’t do.  External insulation does improve the U values of your wall, but it doesn’t very quickly improve the comfort that you experience inside the building, in the way that internal insulation does. 

When you walk into a room, your sense of comfort is defined by a couple of different things.  One is the actual physical temperature inside the room, but the other is very important and is actually the feedback that you’re getting from the room itself.  This is the amount of infrared radiation which is being emitted by all the surfaces around you and that is felt by your skin. 

So even if you apply external insulation to a wall, if you’ve got a very high density masonry wall and you walk close to it, you’ll find that it doesn’t necessarily feel that warm, simply because the wall is absorbing the infrared radiation that’s being emitted by your skin.

Now, if you apply internal insulation to that surface, very quickly you create a surface which warms up much faster and begins to emit infrared radiation back to you.  So, when using internal insulation you actually only need relatively small amounts to provide a big improvement in terms of comfort.

We typically recommend wood fibre insulation because it’s one that we think is by far the best material to use, but there are lots of different materials on the market. 

There are calcium silicate boards, clay boards, cork boards, hemp lime mixes, or insulating plasters.  Then there’s lots of other synthetic materials, such as polystyrene or isocyanurate boards. 

There’s a whole range of different products that are available for internal insulation.

It’s designed predominantly for solid walls, so it would generally be for solid, cavity brick or block walls (all types of man-made masonry).  You can also apply it to the interior of solid natural stone walls. 

It can also be applied to timber frames but how much insulation you can use, does depend on the construction of the timber frame because the way that the membranes are installed in timber frame dictates where the insulation can go. So it’s a bit more tricky in timber frames.

As we’ve worked on old houses and Listed buildings for 23 years, we have generally found that wood fibre is by far the safest material.  It’s not the only material though. 

There are lots of other materials that can be used, but in terms of safety and risk, wood fibre presents the best possible solution.  That is mainly because it’s extremely capable of managing moisture, at moving moisture and it generally keeps the wall below dry. It also very importantly keeps any timbers that are bedded in the wall itself very dry too.

That is one of the most important points about internal insulation because applying insulation to the interior of a building massively changes the way that the walls work. It’s very important that you use an insulation material that can manage moisture and isn’t going to cause either an accumulation of moisture in general, or around specific areas, particularly when you’ve got historic timber or simple floor joists or beams running into the wall which are very sensitive to moisture. If you use the wrong insulation, you can actually cause an accumulation of moisture in those timbers and then eventually that leads to rot. 

We have two different types of wood fibre products. We have the UdiIN2CM board which is a purely adhesively fixed board.  It uses a lime plaster adhesive to bond it to the wall, which is brilliant for loose friable substrates and very soft historic substrates like soft stone or friable plasters or even materials like cob.

Then we have thicker boards which would be products like the Pavatherm Profil.  They come in a 40 mm and a 60 mm board, and these wet processed boards provide high levels of insulation and also a very high capacity for moisture storage and moisture movement, so the boards can dry out very quickly as soon as the weather warms up, and they also disperse moisture within the wall and keep the wall beneath dry – which is obviously a very important factor for historic buildings where you have materials which are very sensitive to moisture.

No, you can’t.  Filling a cavity wall allows moisture to move from the outer leaf to the inner leaf and if you insulate the interior as well, you are preventing any heat that is going into the wall from helping to dry that out, and so applying insulation to the inside of that is quite likely to give you conditions where mould grows and damage is done to the internal insulation boards too.

That’s quite an important question but generally we’ve found that when using thinner wood fibre boards there is no problem.  Using synthetic boards and systems where you incorporate a cavity between the insulation board and the wall, you may well get condensation and mould problems.  It is important to consider, when you’re looking at the materials you’re going to use for internal insulation, that you consider how vapour permeable they are and how able they are to manage moisture and distribute moisture, not just the insulation performance of the material.

Again, the answer is absolutely not.  The dot and dab process creates a void behind the boards. You have the dabs of plaster applied to the back face of the board and when that’s pressed against the wall, you end up creating a little cavity behind those insulation boards which allows air movement, which in turn allows condensation to form and potentially mould growth. That can then lead to problems with mould getting into your inner environment. 

The more insulation you apply to your walls, the thicker it becomes and the less floor space you will have or the more floor space you will lose, and so obviously you should be wary about how much insulation is applied to the inner face of the wall.

Our thinnest board is 23 mm thick and that is the thinnest board that we have available that will give you a big boost in comfort and a reasonably good improvement in heat loss. 

When Building Control are involved, they tend to specify that the minimum U-value should be 0.7 W/m2K for historic buildings, but that can be a lot lower depending on what other works are being done to the building.  It’s really important that when you’re thinking of installing internal insulation that you do talk to Building Control and see what they would like you to target in terms of U values. We can then tell you how much insulation you need to apply to the walls.

Yes, you can, but the more you insulate the interior, the more the section that is not insulated can become problematic.  That’s essentially because as you insulate the inside of the building, raising the internal temperature, you begin to raise the amount of moisture that is in the air and so you increase the risk of getting condensation on cold parts of the building – which are, in other words, the areas that you’re not insulating.  So yes, you can do it in the short term, but in the longer term it is worth doing the whole of the interior so that you don’t have issues with condensation and mould growth in those areas which haven’t been insulated.

That’s a really interesting question because certainly at the thinner layers of insulation – so when we’re supplying 40 mm, 23 mm, anything up to 60 mm really – we generally aren’t too concerned with vapour control. 

From 60 mm onwards, which will give you U values from about 0.5 W/m2K downwards, it is really important to start thinking about vapour control, but it’s also very important to start thinking about moisture ingress from the outside. 

So yes, you do need to think about a vapour control layer and typically we use a product called UdiMultigrund, which is a vapour regulating plaster or a vapour controlling plaster.  That reduces the amount of interstitial condensation that’s going to form in the insulation during the winter. You also need to think about preventing moisture ingress from the outside and that’s particularly important when you’re working on walls which are made of porous brick or porous stone. This is particularly important when using sandstone, as you need to consider how much rain is going to be absorbed in the outer surface and use materials such as facade impregnating creams to reduce the amount of moisture ingress. This prevents problems with a build up of moisture in the walls and problems with frost damage, timber decay and insulation decay in the wall.

Yes it does but possibly to a lesser extent than you might think.  Normally if you’re insulating a masonry wall, the masonry itself will be the best acoustic absorber.  Adding internal insulation will tend to help more if the masonry itself is quite air permeable, so the poorer the pointing in it is, the more benefit you’re going to get from adding internal insulation,  But generally, it won’t make that much difference simply because masonry is a better sound insulator than insulation. 

However, when you’re working on party walls particularly – and this tends to be where we get most queries about sound insulation – the best way to insulate party walls is actually to use a thin timber frame, to use resilient bars and to mount our clay boards on those bars. 

That works two-fold.  You’ve got the resilient bars providing an air cushion between the clay boards and the structure underneath.  You can use wood fibre wool in the timber frame beneath to absorb air borne sound and then the clay board mounted on the surface again absorbs a lot of air borne sound and provides really high levels of sound insulation.

That concludes this week’s show.  If you have any further questions about this topic or sustainable building materials, please feel free to email at [email protected] or alternatively give me a ring on 01392 861763.

The post A Guide to Internal Wall Insulation appeared first on Fibres.

Subscribe to our podcast on iTunes and never miss another show.

We’ve developed the first free, online wood fibre insulation course. Designed for architects, builders and self-builders, the course covers how to specify, source and use wood fibre effectively.

If you’re working on a building project and need help specifying your materials, checkout the following.

Air tightness essentially is a measure of how much air leaks out from the interior of a building when there is a pressure difference between the interior and the exterior. 

Now, that doesn’t mean that air only leaks out when someone is blowing air into a building or pushing air out of the building. 

Wind actually is the main driver of pressure differences between the interior and the exterior, so when wind blows against one face of your house you get a positive pressure on that face that pushes into the building.

On the opposite face of the building you actually have a negative pressure which is sucking air out of the building. 

So with any slight breeze even, you begin to get a pressure difference between the inside and the outside of the building and you begin to leak air out of your house.

Also, in winter, when you turn the heating on, heat rises.  It builds up pressure in the upper rooms of a building and that draws in air at the bottom. 

So in the lower rooms in a building you’ll be drawing air in. 

You’ll have a lower pressure there, and again that produces a pressure difference even when there isn’t necessarily any wind blowing outside. 

The basic assumption is that air tightness is really only necessary for passive houses and that means it’s really hard work and not something that is applicable to an ordinary house. 

This is where air tightness is not well understood.

Air tightness and controlled ventilation losses account for 15 to 20 per cent of heat loss, so it’s a really significant amount of heat to lose from a building.

By reducing ventilation losses (air leakage through the fabric of the building) you actually end up with much better air quality.

The warm, moist air that is in your building during the winter leaks through the walls, whether they are masonry or timber frame, it then condenses and increases moisture levels in the walls.

That can cause mould growth and damp, which again can affect the internal air quality. 

So by reducing that you do actually end up with much better air quality, which is counter to what most people expect when they think of a building that is very, very well air sealed. 

And also by reducing these draughts, you end up with much higher levels of comfort. 

You don’t get the draughts and the cool air down at ground level and the hot ceilings that you get during the winter with the heating on. 

You end up with a much more even temperature from floor to ceiling, so you avoid the cold feet and hot head issue that you often get in the winter. 

And the same happens in the summer.

By preventing draughts and air leakage in the summer you can keep your house cool on extremely hot days. 

So during a heatwave if it gets up to 30+ degrees outside, the last thing you want to do is open all the doors and windows because you actually then let all that heat into the building. 

Ideally you keep the building closed down during the day and you open it up in the evening, so it then stays cool.

Finally, you reduce your heating and energy bills by making a building much more air tight. 

Your heating is not working so hard to replace all the warm air that’s leaking out of the walls and you keep the building at a much more even temperature. 

Obviously you do need to ventilate the building properly. That though is generally done with a ventilation system, certainly in newer buildings, and they can also be installed into older buildings too.

A mechanical ventilation system with heat recovery is really the only way that you can properly ventilate a building and ensure that you’ve got good levels of air quality all the way through the building.

Trickle vents in windows or just leaving any window open somewhere in the house is really not good enough to ventilate the whole building and provide good air quality throughout an entire house.

With timber frame buildings you typically use membranes, or vapour control air tightness membranes and a lot of tape.

The tapes are generally an acrylate adhesive, so it’s a clear adhesive (a very, very sticky material). 

We would specify the Ampatex Sinco or DB90 Vapour Control and air tight membranes to achieve those levels of air tightness. 

Or you can use products like the Smart Ply Vap Air Tight, which is an air tight OSB board, so that gives you racking resistance.

So it’s a structural board, plus the board is also air tight and so you simply tape the joints onto the board.

This gives you a really air tight building as well.

And then finally you can use OSB3. 

Just use ordinary OSB3 for projects where the air tightness is less important but you still want to achieve reasonable levels of air tightness.

When you’re jointing the membranes or the OSB boards, we’d normally recommend the Ampacoll XT which is an acrylate tape.

It’s extremely sticky and sticks to any dry surface like clean timber, the boards or membranes.  It’s a really good tape for joining any two items. 

In terms of around awkward areas such as window and door reveals or internal corners, we tend to use a split back tape. 

That’s a tape which has the backing paper split into different widths so you can peel off one section, stick it to one area (such as a window frame) and then peel the rest of the backing off to stick it to the window reveal.

This makes it a lot easier to actually use these tapes and use them effectively to make the junction air tight.

When you’re trying to seal around penetrations, butyl tapes tend to be a lot more useful. 

They’re very, very flexible and very, very sticky.

You can also use them in areas where the moisture content is quite high, so low level externally plinth areas, and essentially you can stretch the tape out. 

It’s almost like chewing gum on a roll, so you put it on the pipe and then stretch it out and seal the junction around the base of the pipe.

We’d normally recommend the Ampacoll BK535 which is a fantastic tape. 

It’s the stickiest butyl adhesive I’ve ever come across, and also one of the stretchiest. 

It stretches out and makes it so easy to seal around pipe penetrations, cables, vents or ducts. It’s absolutely fantastic tape.

In masonry you tend to use plaster as your air tightness layer because you’ve got a solid wall and simply plastering it is enough to make it air tight. 

So you tend to use membranes less on masonry. 

You still need to use them on roof structures, on the underside of roofs and on suspended floors, but masonry walls themselves you can actually stick with plaster.  Taping around doors and windows and sealing it back against the masonry is more often than not, the job of the butyl tape. 

We’ve got a product called Ampacoll F which is really thick stretchy butyl tape and goes around the outside of the window before you put it in. 

Once in situ, you can peel off the backing. It’s a double sided tape, and that allows you to stick it to the reveal of the masonry and gives you a really effective air tight seal. 

Complete air tightness is not something that can be achieved by simply walking into a house and changing a few things.

In existing buildings, it’s the seals around openings, appliances and those obvious things around your doors and windows that need addressing first.

However to actually make the building fabric itself air tight, you’ve really got to strip it back to the bare bones of the building. 

You’ve got to be able to get to a junction between your window, your door frame and your walls. 

You’ve got to get to the junction between your ground floor, walls, roof, and any junctions around floor joists or first floor joists, where they meet the wall or actually rest in the wall.

So air tightness is not something that’s terribly easy to do on an existing building, unless you actually are refurbishing the whole building and you’re going to strip it back, but it is perfectly possible.

Generally it’s done with what’s called a ‘blower door’ test.

This involves putting a frame with a membrane in a doorway and in the middle of that membrane, placing a big fan.

The fan blows air into the building and you then measure the air flow into the building.

That’s called a positive pressure test and then you do a negative pressure test which is where the fan is sucking air out of the building to measure the air flow out of the building. 

You then average the result for the two and that gives you the overall air tightness level of the building.

When you’re doing air blow door tests, it’s actually really important to think through every single possible cause of air getting in or out of the building. 

There’s obvious ones such as flues or vents and the obvious things that you can see, but there’s plenty of things that are hidden that you also need to be aware of. 

One of the biggest problems that we come across are non-return valves in waste pipes. 

A Durgo valve is one, which is an air admittance valve which allows air into foul drainage.

Whenever you flush the loo it allows air to come in behind the water so you don’t get a vacuum forming. 

There are also waterless traps, so Hep20 do a great space saving trap which goes in your sink or in your shower trap.

It’s essentially a rubber membrane which seals again after the water’s gone through it, but crucially it doesn’t prevent air going out through it again in a positive pressure test. So that’s an important one to address.

You’ve also got things like the ventilation system. 

If you’re doing a new build or you’re putting a ventilation system into a building, you’ve got to tape up the intake and exhaust ductwork on the system. 

There are then the obvious things like making sure all the windows and doors are actually locked so that you fully engage all the seals.

Then there are traps. If you’ve got U-bends, you’ve got to make sure they are filled up with water.

If you’re using the waterless Hep20 traps then you either tape up the actual trap itself or you can go and address it from the outside, by putting a drain bung in and preventing any air flow out through the main soil pipe.

There are two different ways of measuring air tightness.

There’s an n50 test and a q50 test. 

N50 is a measure of the volume of air leakage at 50 pascals of pressure, so in the blower door test the fan either drops or raises the pressure in the building to 50 pascals above or below the external pressure. 

That gives you a result and it’s measured in air changes per hour.  That’s generally used for passive house certification.

The UK building regulations require a slightly different test and that’s the q50 test. It’s a measure of the air permeability of the building fabric. 

It’s measured in cubic metres per hour per sq. metre.  Again, when using the blower door test, you should look for a drop or rise in the pressure in the building of 50 pascals above or below the external pressure. 

Generally the q50 is always required by building control even if you are building a passive house, but for passive house certification it’s actually only the n50 result that is used. 

For passive house certification you need to achieve an n50 of less than 0.6 air changes per hour.

For UK building regulations you need to have a q50 of less than 5m3 per m2 per hour, which on average equates to a q50 of around 4.5 air changes per hour, which is not a particularly high target.

If you’re installing a ventilation system in a non-passive house building I’d suggest aiming for an n50 of around 1 air change per hour or a q50 of around 1.1m3 per m2 per hour.

That concludes this week’s show.  If you have any further questions about this topic or sustainable building materials, please feel free to email at [email protected] or alternatively give me a ring on 01392 861763.

The post Air Tightness: The Complete Guide appeared first on Fibres.

Subscribe to our podcast on iTunes and never miss another show.

We’ve developed the first free, online wood fibre insulation course. Designed for architects, builders and self-builders, the course covers how to specify, source and use wood fibre effectively.

If you’re working on a building project and need help specifying your materials, checkout the following.

Hello, and welcome to this week’s ‘Back to Earth’ podcast with me, Chris Brookman. This the show for architects, builders and surveyors all about the use of sustainable building materials. In this episode specifically we’re going to be answering questions all about cavity wall insulation. 

Cavity wall insulation’s a topic that I get asked an awful lot about and come across a lot of situations where it’s used either inappropriately or it isn’t used when it should be used. 

So I’m going to answer all the questions that we’ve been asked over the last year or so and hopefully answer everyone’s questions about it.

There’s two different types of walls essentially. You can have solid walls which are literally a solid brick thick, or you can have a cavity wall which is essentially two walls – so you’ve got an inner skin of normally brick or block, which is normally about 10cm thick. You then have a cavity which can be anything between 50 and 100 ml wide, and then you have the external leaf which is another 10cm of brickwork or blockwork.

The idea of having that cavity is to prevent moisture from moving from the outer skin and migrating towards the inner skin. So that cavity allows any moisture that gets through the outer skin to drain down and go down into the ground before it manages to reach the inside skin.  It was a way of drying out buildings when there was no insulation in them basically.  It kept the weather out from the outside and it kept the interior relatively warm compared to having a solid wall.

Well, it’s very, very, very basic. It essentially just fills that gap between the two walls. There are various different forms of it and actually there’s a lot of reasons why it should be carefully considered.

It’s something that I get asked most often actually.  I would generally say that you should only ever fill a cavity wall if you’re going to externally insulate a building.  If you’re not adding external insulation, then I would generally recommend that you never, ever, ever fill a cavity wall. It’s there for a reason.  It’s keeping the building dry and it really should not be filled.  The reason for that is very simple – if you fill that cavity, moisture can then track from the outer skin all the way through and actually reach the inner skin, and also any moisture that escapes from the building during the winter months and gets into the cavity will condense in the cavity and that moisture wets the insulation and again that migrates back towards the interior.  So adding cavity wall insulation can potentially actually give you damp problems.

Well, there’s various different types. You can inject polyurethane foam into your cavity. You can blow different types of fibre – different types of fibreglass, normally, into the cavity. You can also blow polystyrene beads into the cavity and those are the main ones.

In terms of which is best it really depends on how well they’re installed because actually they’re all pretty good at what they do. But I have to say my money’s probably on the polystyrene beads, and that’s simply because polystyrene beads flow. It means that if you basically pour the polystyrene beads in at the top of the cavity, they will work their way all the way down to the bottom and they’ll also go under things like window sills so you actually get insulation properly worked in under the window sills.

You can also get slightly greener alternatives. There’s a product called Kenwood CW1000 which is essentially a mineralised woodchip and again it’s quite a fine material that can be blown into a cavity and because it flows, again it will get under the window sills, but it’s made from woodchips basically and so is a rather greener alternative.

The one important thing to bear in mind is that this product can’t be left in contact with the ground, so you generally have to put in a certain amount of synthetic insulation at the bottom of the wall to prevent that material from going down into the ground.

Well, that depends generally on who’s installing it. Most of the time you can get grants for that kind of insulation.  If you can’t, I guess you have to look around for competitive quotes, but generally the cost is pretty minimal, basically because it’s covered by the grant.

If you buy a house that already has cavity wall insulation, I would look at it very, very carefully, particularly for damp issues internally.  There is one simple way of rectifying any of those problems and that is quite simply to put external wall insulation on, and that will warm up the cavity inside. It will allow it to dry out and it will rectify the problems that are experienced inside.  That’s a slightly simplistic way to discuss it, but in essence that’s exactly what happens.

Generally full fill cavity insulation is something that you build in rather than blow in afterwards.  Full fill simply means that when you’re building the wall, you’re fully filling the cavity between the inner and outer leaf rather than leaving an air space between the insulation and the external leaf, as was common.

Actually it does.  Most of the time the installers notify Building Control but if they don’t, it is a notifiable procedure. So it’s important that Building Control are involved in it and have notification of it.

Generally it doesn’t.  There’s no reason that it should break down and degrade into anything else, but if alterations are carried out to the building and the cavity wall insulation is allowed to come out of the cavity, then it will need topping out and some of it will need replacing. So, generally not unless it’s disturbed in some way or lost.

Generally not. If anything, it’s more likely to cause damp unless you’ve got external wall insulation.  So that’s basically a no. 

Mice and rats generally will move through anything. It doesn’t matter whether it’s synthetic or natural.  If there’s a source of food there, they will tend to move through it.  So, no, again it won’t stop rats.

Generally not because it will tend to allow moisture from the exterior skin to reach the interior skin, again, unless you’ve got external wall insulation.

Potentially it can do, if some of your noise is being transmitted through the actual wall.  But what you tend to find is that noise travels mostly through windows, through roofs, through air bricks, through doors, that kind of thing.  So it has the potential to reduce some noise transmission through a wall, but most of the time it will be pretty minimal.

The answer is actually yes.  It does take a long time because the materials that you use for cavity wall insulation are extremely poor at moving moisture around and allowing themselves to dry out. But generally, yes, it will slowly dry out, so if you have a situation where you’ve got wet cavity wall insulation, the best thing to do really is to install some external wall insulation and preferably a vapour permeable wall insulation to warm up that cavity and allow it to try out.

Well, one would hope so, but as per my previous comments – only if you have external wall insulation, because potentially the additional moisture that can migrate through it, will actually negate that additional benefit of warmth.

Yes, it can actually, and actually now that there have been so many buildings with it installed and so many of those buildings are having problems, there are actually companies now that go round and remove it.  As I said, unless there are serious structural issues, I wouldn’t remove it. I would simply add external wall insulation over it and allow it to dry out. But potentially there can be issues with the rusting of cavity wall ties, which are definitely exacerbated by wet insulation.  So if you need to, then absolutely you can remove it.

Generally it doesn’t cause condensation but it allows the passage of moisture from the outside to the inside. So, I would have said, no, is the answer to that.

To summarise, basically what I’m saying is cavity wall insulation is only recommended, certainly by us, if you’re adding external wall insulation and that’s all about the moving of the due point from the cavity to out into the external insulation so that you don’t condensation in the cavity in the winter.  And it also is about preventing driving rain and most moisture actually reaching that external leaf of the wall, which then can track through to the inside. 

So with that external insulation on there, you can be reasonably confident that you’re not going to be getting moisture tracking through from the outside and you’re not going to be getting condensation forming in the cavity in the first place – which would track back in as well.

So if you aren’t adding external wall insulation, the best thing you can do is use internal wall insulation but definitely do not fill the cavity.

That concludes this week’s show.  If you have any further questions about sustainable building materials or cavity wall insulation, please feel free to email me at chris@backtoearth or alternatively give me a ring on 01392 861763.

Thanks for listening!            

The post Cavity Wall Insulation: The 16 Key Questions appeared first on Fibres.

Subscribe to our podcast on iTunes and never miss another show.

We’ve developed the first free, online wood fibre insulation course. Designed for architects, builders and self-builders, the course covers how to specify, source and use wood fibre effectively.

If you’re working on a building project and need help specifying your materials, checkout the following.

So, in this episode I’m going to take a bit of a departure from the usual line that I go down in looking at the different issues, and actually look to the future. There’s so many exciting new developments in construction that are taking place, that really have the power to revolutionise how we build buildings and create buildings that really without that sort of technology, we wouldn’t be able to produce otherwise.

One thing that’s really caught my eye is 3D Printed Construction and its ability to create buildings that you really couldn’t create otherwise from bricks or blocks or timber frame panels – very curved buildings, domes, all sorts of different shapes that really can be quite challenging to produce.

So why would you 3-D print a building? Well, the technology has the power to remove a lot of the vagaries from building sites. Your 3-D printer doesn’t turn up one morning with a bad back or having been down to the pub the night before and be a bit off, and all the crazy things that happen on construction sites across the UK certainly. It will work 24/7. It simply needs to be fed with the right feed stock for printing the building, so the various different materials that it can use, and it produces very precise buildings. There’s virtually no waste with it, other than the small amount of waste that’s left in the pipe between the pump and the printer effectively, and it can produce very strong, very structurally sound, buildings using effectively very small amounts of material.

So the 3-D printing is done by a 3-D printer and that seems to take the form of various guises. Currently there are various different companies producing 3-D printed buildings. Some are actually printing them on site, so some are laying a layer of insulation such as foam glass, that kind of material, an aggregate. Printing a foundation over the top of it, which is then backfilled with concrete and then continuing on to print the ground floor walls, which are printed over the top of the foundations. Coming up to the top of the ground floor walls, a first floor structure is built, potentially pre-fabbed off site and literally just craned on.  And then the second floor can be added through 3-D printing, all the way up to eaves basically. That’s essentially where it finishes.  As far I can tell, currently there aren’t any companies that are printing any roof structures. Those are largely pre-fabbed off site and then craned into position on site to create a weather tight shell.

Some of the other companies are looking at putting down a ground floor slab. So basically a reinforced slab and then just coming straight up off of that. But there’s a whole plethora of different companies doing slight variations on essentially the same theme.

3-D printing is also called ‘additive manufacturing,’ and it basically involves using a computer-controlled print head and when you’re building buildings the print head is obviously quite large, but it’s very similar to how you would ice a cake with a piping bag. It basically has a computer-controlled print head which is fed with a continuous feed of fast setting concrete and the computer moves the print head around and effectively prints a continuous sausage of the cement and slowly that’s built up in layers until you reach whichever height. The walls tend to be made up of an internal and an external skin which are formed by printing these layers and then in between you have a latticework structure, much like a truss beam kind of structure.  And this makes for a very strong structure vertically and horizontally, but of course being made of cement, thermally it’s not really that good. It’s better than solid concrete or concrete block, but it still has significant thermal bridges between the interior skin and the exterior skin.

In addition to that, you are of course using cement concrete, so whilst you’re being much more efficient with how you use it, you are still using something that is relatively polluting. However, in Italy there is a company who are working and doing very well with printing with clay. I think they’re largely targeting the third world in what they’re doing, but they’re sieving soils, local soils, mixing them to a fairly precise consistency and then using a screed pump to pump that through to the print head and force that out through the nozzle in exactly the same way that people are doing with cement.

Obviously because it’s earth, the main difference is speed. You certainly can’t print with earth as quickly as you can with cement because the setting time is as long as it takes to dry as opposed to half an hour or an hour with the fast-setting cement.

And that’s really where my interest lies in moving forward in some involvement for Back to Earth with how we can create products that really can be used in this way and progress construction.  My own background is in cob construction many years ago, which is clay and straw, and if we can produce a material that combines the properties of earth which actually are really, really useful in construction with regards to acoustics, thermal mass, heat storage and the way that it can temper the internal environment of the building – if we can combine that with a fast-setting material, then we’ve got something that is really applicable to the modern environment but isn’t damaging in the way that cements are.

This whole sector is actually moving quite quickly now and the size of the 3-D printing machines is growing all the time. I think the biggest one that I’ve seen so far is about 12 metres tall. So you really can build some pretty big scale buildings using these sort of methods. So this is a space that’s going to develop quite quickly and it’s going to bring up ethical issues as well as constructional challenges because a lot of people are employed by the construction industry and obviously these kind of disruptive technologies would push a lot of people out, certainly to doing different jobs. But as with many industries, automation brings much higher quality and doesn’t necessarily have to massively reduce the work force.  It just hones it and turns it into a different and arguably more skilled work force.

So, an interesting space that’s really worth watching over the next few years.

That concludes this week’s show. If you have any thoughts on 3D printing and it’s application in construction, I’d love to hear them. Please feel free to email me at [email protected] or alternatively give me a ring on 01392 861763.

You could even join me in discussion on Twitter – @backtoearthsw

Thanks for listening.

The post A Look into the Future of 3d Printed Construction appeared first on Fibres.

Subscribe to our podcast on iTunes and never miss another show.

We’ve developed the first free, online wood fibre insulation course. Designed for architects, builders and self-builders, the course covers how to specify, source and use wood fibre effectively.

If you’re working on a building project and need help specifying your materials, checkout the following.

In this episode specifically, I am going to be talking about the various different manufacturers of wood fibre insulation, the differences in their products and the similarities in their products and also all the things that you need to consider when you’re buying your wood fibre insulation.

So firstly, there are various different manufacturers.  If you Google around, you’ll probably come across four or five.  The main ones that you’d come across would be Unger Diffutherm, Pavatex, Styco, Gutex and there’s a company called Schneider as well, who sell through in Ireland.  Each different company tends to sell through a different distributor in the UK and obviously each different distributor is going to want to say, “Well, our system is better than the others because of X,Y and Z.”  But in the last 10, 12 years of being in this industry, you do get a feel for the differences between the systems and generally they all sell good quality products.  They all have to meet a minimum manufacturing standard, so obviously that’s there to ensure that the products are a good quality, and they all have different boards as well.  So different manufacturers concentrate on a different type of board for different purposes.  Generally you’ll find that each different manufacturer is probably suited to a different type of project or slightly different type of project, which may or may not be more applicable to what you’re doing.

Whilst each different manufacturer has a different product range slightly, they all are essentially very similar in a lot of ways – but the biggest difference that I’ve come across really is actually the way in which the board is manufactured and less so, by who.  As I’ve said previously, there are two different ways of manufacturing wood fibre boards. 

Now the first process is wet processing and essentially you take chipped timber – so all waste timber – you grind it up and then you boil it up with water and a few other chemicals designed to break down the timber into the fibres. You strain that and you’re left with the wood fibres themselves and then you pour that onto what is essentially a sieve.  You compress it down to a 20ml layer and then you steam it.  That 20ml layer is held together purely by the lignin around the wood fibres, so that’s the lignin from the tree. That holds the whole board together and then to make thicker boards you simply laminate up the 20ml boards into thicker boards.

Now, wet processing creates a product where the fibres are essentially in a very similar situation to how they are in the tree.  They’re quite well connected to the neighbours and so that means that one fibre can transport liquid water from itself to its neighbour and so on down the chain, and actually enables it to transport liquid moisture very, very quickly.  Now that has really useful applications in certain scenarios and equally that can be a problem in others.  So, it’s just to be aware that that’s how wet process wood fibre works.

Now the other alternative essentially is dry processed wood fibre boards.  These are made in the same way, so the initial process is to take your chipped timber.  This is then dried and ground up, refined, and then it’s sprayed with a PMDI glue.  That’s essentially a polyurethane glue, but so as to not completely waste my chemistry degree, PMDI stands for polymeric methylene diphenyl disocyanate.  As I say, that’s essentially a type of polyurethane, but it’s used in a lot of products.  It’s used in MDF. It’s used in OSB. It’s a very widely used glue.

Now commercially obviously you want to use as little as possible to create your product because it costs money, but the biggest difference between them is that each individual wood fibre tends to be wrapped around with a coating of this glue and so it’s very, very, very much less able to transport liquid moisture.  One fibre can’t transport it to its neighbour because it’s got this barrier of glue in the way.  That has really useful applications actually. A board that doesn’t soak up water is very useful in certain scenarios, but equally there are other scenarios where the transport of liquid moisture is actually a really important property of the board.  So it’s just to be aware that wet process and dry process boards are not interchangeable in all scenarios.  In some scenarios they are absolutely, but certainly not in all. Important to know that.

Unger generally concentrate on wet processed boards.  Pavatex used to concentrate primarily on wet process but now have a big mix of the two.  All of their internal wall insulation systems tend to be wet processed, but everything else pretty much is dry processed.  Styco, again, similar mix. Gutex and Schneider tend to be predominantly dry processed.  So be aware that when you’re buying from those companies, you do need to look at how it’s manufactured.

You’ll tend to find that dry processed boards are much cheaper than wet processed and that’s simply because of the amount of processing involved means that the product just doesn’t cost as much.  This is what’s driving certainly some of the commercial decisions about which boards to supply and obviously develop the market with those boards.

So once you’ve decided which type of board to choose, it’s important to go through the manufacturers and actually look at their technical detailing and their recommendations for installation and really to see how detailed that is.  Some manufacturers are quite vague about how you install their products and there’s not a lot of detailed support.  Some others are actually very good at helping you install the board. They give you a lot of information about how to install the product, where to install it, where not to install it and there’s a lot of detailed support.  This essentially demonstrates that the manufacturer has a really good grasp on how their product should be used and how they can help you to install it.  So that’s a useful thing to look at.

Unger are pretty good at that.  Pavatex are pretty good at that. Styco are reasonable. Gutex and Schneider, I’ve been less able to find about theirs, to be honest.  Not that there’s anything wrong with the product, but I’ve certainly not found the detailed understanding that you would generally come across from maybe the other three.  So again, once you’ve decided on the manufacturer, the other things to consider really are the components.  So again, most of them do tapes and membranes, certainly Schneider, through Partel do a big range of membranes and tapes.  They’ve got obviously a good support with all the components.  Again, Gutex as well with Ecological have a huge range of air tightness products, so really good support on that side – and the other three do as well, Unger, Pavatex and Styco, generally all sell the air tightness side.

The final thing really is if you’re looking at renders, different manufacturers use different render systems. Some are their own specific render, some use a third party’s render that has been tested onto wood fibre.  It depends whose system you’re going for as to which render you’ll end up looking at.  Often really useful to get a good understanding about render, what it looks like, how it’s put on, how it compares to the way that other people use their renders.  Now, generally most render systems that go onto wood fibre are pretty thin, so you’d use a thin layer render, typically 5 to 6ml along the basecoat and then between about 1 and 3ml on the finish coat.  There are some systems that have got anything up to 20, 25ml on the render systems, which rings alarm bells for me – mainly because it’s the only one on the market. I would tend to stick with the thinner render systems, also partly because wood fibre tends not to carry a huge amount of weight like that.

Anyway, so hopefully that gives you some idea of the things to look at when you’re choosing your manufacturers and if you have any further questions about sustainable building materials, please feel free to email me at Chris@backtoearth or alternatively give me a ring on 01392 861763.

Thanks for listening.                 

The post Choosing the Right Wood Fibre Insulation Manufacturer appeared first on Fibres.

Wood fibre insulation 101

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We’ve developed the first free, online wood fibre insulation course. Designed for architects, builders and self-builders, the course covers how to specify, source and use wood fibre effectively.

If you’re working on a building project and need help specifying your materials, checkout the following.

Hello, and welcome to this week’s ‘Back to Earth’ podcast with me, Chris Brookman.

This week I’m going to cover a presentation that I did to the Green Register and the ASBP in Bristol, which is basically a wood fibre 101 which really goes into detail about wood fibre, the way it’s manufactured and all the different uses of it.

What exactly is wood fibre? 

Wood fibres are made from tiny cellulose microfibres, so these are short sections of cellulose in a long chain and they’re held together with a lignin resin which is a natural resin that is part of the tree.  They create structures which are almost like long drinking straws – very, very small obviously – and these are called xylem.  These essentially in the tree are for transporting moisture from the roots all the way up to the branches at the top and out to the leaves.  They can transport huge amounts of water a very, very long way vertically, which means they’re incredibly good at transporting moisture.

Now, on water you get a really high surface tension and that combined with the hydrophilic nature of the wood fibres, creates a way of transporting huge amounts of moisture very, very quickly.  But also because they’ve got a huge surface area, the wood fibres, you can also adsorb a vast quantity of moisture vapour onto the surface of them. 

Wood fibres also have unusual phase change properties.  So when water is adsorbed onto the surface of them you get a certain amount of heat released and it creates some really unusual properties, which mean that wood fibres behave significantly differently to synthetic fibres, for example.

Wood fibre also has a very high specific heat capacity, which means its ability to store heat for a given quantity or a given mass.  That’s actually increased as it adsorbs water as well, including a small amount of moisture in the process actually boosts the thermal mass of the fibres.  This and the fibres’ ability to manage moisture makes it incredibly useful for retrofit because they are very good at keeping existing timbers dry.

So natural fibre structures, the plant fibres, are incredibly complex – much more complex than synthetic products that we create and that gives them really, really useful properties over a wide range of areas, which is why they’re so useful in insulation and building products.    

So how is wood fibre insulation made? 

There are essentially three different types of wood fibre.  There’s a wet processed rigid board.  There’s a dry processed rigid board and there’s the flexible wood fibre which is a thermally bonded non-woven product.

The wet and dry process, as I said, are used for making all sorts of rigid boards of all sorts of densities and the non-woven process is used for all sorts of different flexible wood fibre products of all sorts of different densities, again depending on what the application is. 

Now for the wet processed boards, essentially you take wood shavings, wood chips, all sorts of offcuts, all sorts of waste wood effectively.  It goes through something called a refiner which grinds the wood up into very small pieces.  This is mixed with water and essentially boiled up and that releases a lot of the water-soluble compounds in the wood which are then removed, and then they add certain additives depending on what the properties they’re looking for are.  This goes onto essentially a big straining bed and the moisture is sucked out of it and pressed out of it, and then that goes through a dryer and a steamer and all the wood fibres are steamed and essentially bond to each other loosely.  That forms 20ml boards which are then laminated up to different thicknesses.

The dry processed boards go through a similar process to begin with, in that the waste timber is refined, but then that is actually dried. It goes through a big dryer and then gets mixed with a polyurethane resin which is then spread out onto a conveyor, graded to an even thickness and then squashed down to its final thickness and then cured in an oven again with steam and machined up to the final size that you need.

Now those boards are produced as a homogenous board and they can be produced to any thickness pretty much, but they are a single layer all the way through, whereas the wet processed boards are always a multiple of normally 20ml. 

Finally, the flexible wood fibre products – so the thermally bonded products.  Essentially the wood again goes through a refiner and is ground up into coarser fibres that go into the wood fibre board.  That’s blown with a polyester fibre into a slab. That material is heated and gently pressed and the polyester fibres soften and glue the whole structure together.  You can produce anything from 40ml up to 240ml thickness, so you can produce some quite thick material with that.

All three different processes do produce quite different products and they all have some unusual and very, very differing properties.  Looking at the wet processed boards, they tend to range from 140 up to 250 kilos per m3 in density.  The dry processed tend to be slightly lighter, between 100 and 200, partly because to achieve the same mechanical strength you don’t need quite as much material because the polyurethane glue is doing the job.  And then the flexible bats tend to range between about 40 and 60 kilos per m3. 

Now the specific heat capacity is roughly the same for all the boards because they’re nearly all timber, but because the density varies then obviously the amount of heat storage each product can have, obviously is quite different.  Looking at the wet processed boards, the vapour diffusion coefficient form is between 3.5 and 5.  The dry processed boards are actually slightly more vapour permeable because they tend to have a slightly more open structure and be slightly less dense.  They have a diffusion resistance coefficient of around 3 and the flexible bats tend to be about 1, so they obviously are very vapour open.

However, the main difference really between all the products is the liquid transport capability.  So wet processed boards, they’re quite dense.  The fibres are as they are in the tree and they are extremely capable of moving moisture.  So if you do get moisture into your insulation, those boards will quickly soak it up and transport it through the structure and allow it to evaporate out. 

The dry processed boards, whilst they are very vapour permeable, are not able to transport moisture very quickly, simply because the polyurethane resin coats the individual fibres and prevents transfer of moisture from one fibre to the next. 

The flexible bats are kind of in between the two really.  They’re quite a loose material in terms of the fibres aren’t very close together, so they’re not quite as good at transporting moisture.

Then finally the compressive strength of all the boards tends to be engineered depending on what the final use is.  Simple squarage insulation tends to be about 50 Kilopascals and when you’re going up to roofing, sarking boards, then they can go up to anything around 200 to 280 Kilopascals, which is pretty strong.

In terms of use, the wet and dry processed boards are used for roof insulation externally and internally, for wall insulation and floor insulation.  So anywhere that you can use obviously a solid, rigid board.  Dry processed boards are generally not used for internal wall insulation though, because of their inability to transport liquid moisture. 

The flexible wood fibre that is produced is nearly always used as an insulation between timbers.  This is quite a solid material, so you tend to get a very good friction fit and it doesn’t slump at all.  So with those different products you can do all sorts of different construction.  You can do flat roof construction, both vented and unvented. Externally you can have rendered facades or clad facades.  Again, you can use it on the roof with tiles or zinc or green roofs, and then typically down to plinth level you would take your wood fibre down to DPC or thereabouts.  Anything below DPC and ideally anything less than 300ml above ground level, you would switch over to polystyrene or extruded polystyrene, so that you don’t get any issues with moisturing.

Wood fibre boards and wood fibre products generally allow you to build extremely simple timber frames.  That’s really one area that the product works exceptionally well.  Typically you would have a timber frame depth upwards of 140ml, depending on your target U value.  The rigid boards would then go on the outside of that timber frame. Now the way that you detail the boards around your openings as a standard detail, gives you incredibly low C values.  So typical accredited construction details would give you C values of 0.15 watts per metre per Kelvin, whereas with wood fibre you’re looking at 0.3.  So you’re looking at an 80 per cent reduction in heat loss around your openings in your timber frame.  That allows you actually to target much higher U values than you would with for example a PIR board in between the frame, simply because you’ve got significantly less heat loss around the openings. 

The other property of the wood fibre that really makes it excel is the high density.  Now, if you use those high-density boards externally, they obviously keep you warm in the winter- which is the easy bit, but they also store a huge amount of heat in the summer.  So during the summer they will, depending on the thickness, store most of the day’s heat from the sun and they actually prevent that from entering the building.  Then as the external environment cools, the heat then gets radiated back outwards again.  So using wood fibre you can turn what is essentially an extremely lightweight structure, a timber frame, into something that behaves much more like a masonry structure, something that’s very, very thermally massive, so you create a very stable internal environment.

Now the wood fibre insulation can be used on the outside of masonry as well, just as well as in timber frame, but I’m going to look at internal wall insulation because it’s a bit more interesting than the external.

Typically if you were using rigid boards, you would flatten the wall first with a render layer and then apply the wood fibre insulation and then you render over the top of it.  Or if you’re using the UdiRECO system, you would fix that straight back to the wall.  The board will accommodate the unevenness and then again you render onto that board.

Now essentially what happens during the winter months normally, is that moisture in the air inside the building migrates slowly through the wall or through the insulation and meets your masonry.  Essentially it begins to condense at the interface between the insulation and the wall.  To prevent too much moisture accumulating there, most systems include some sort of vapour control air, so with the UdiRECO and the UdiIIN system there’s a vapour controlling plaster and with the Permatex systems there’s a latex layer within the board that’s slowing the flow of moisture into the wall.  Essentially you get an accumulation of moisture at the interface between the wood fibre board and the wall, but because of the huge storage capacity of the wood fibres that is then stored during the winter months without any detriment to the thermal insulation properties of the wood fibre or in terms of its structure.  In other words, it’s not going to rot.

As the weather then begins to warm up in the spring, you begin to get more moisture movement.  The sun shines against the wall and that will actually dry some of the moisture back towards the interior, but then as you get warmer winds that also begins to draw moisture out of the walls, so the walls dry back out again.  By the middle of the summer the walls are essentially bone dry again. 

If you calculate the U value that you would expect for a wall just using standard conductivity of wood fibre, you would get a particular U value.  But what tends to happen with internal wall insulation only, and only on the inside of masonry, is that you get an increase of performance anything between 20 and 50 per cent, depending on the thickness of the board.  Actually the improvement is more significant the thinner the board, so I’m guessing it’s an effect that occurs at the interface between the board and the wall.

Now we’ve got several long term studies that indicate savings well in excess of savings that you would expect by simply reducing the U value, simply because the walls are performing that much better.  We’ve also measured walls with our own U value testing kit.  We started with a brick wall that had a U value of 4.25 when we measured it, which actually was worse than we calculated.  With our 23ml UdiIN 2cm board we were expecting it to achieve a U value of 2.1, but when it was measured the U value was 1.4. So it was performing about 30 per cent better than we actually expected.  The 23ml board actually reduced the heat loss through the wall by about two thirds.  Now that is a huge saving for such a thin board and it’s all down to the special effect that you get with the interaction between moisture and wood fibre when it’s in an internal situation.

This isn’t a detrimental process, the boards last a very, very long time in multiple decades.  It’s not a process of absorbing water and the boards getting wet and slowly decaying.  So this is something that happens year on year, but when I finally find out exactly what the process is, I’ll let you know.

Finally then, why is wood fibre so useful?

PIR and very high performance insulation can create very, very thin structural elements, but it’s literally only on thicknesses is the wood fibre outperformed by things like PIR.  On every other metric, so acoustics, diffusivity, moisture management and things like achieving as design performance, on site risk from rain and moisture, fire risk even and also environmentally, every single one of those other metrics, would fibre outperforms essentially everything else, or every other synthetic material.

For a given U value, wood fibre has almost twice the decrement layer of mineral wool and at least 65 per cent more than PIR.  So essentially if you have two walls that have the same U value, it will take twice as long for the heat to get a wood fibre wall as it will through a wall using mineral wool.  How that translates to a building is that during the summer you end up with a building that essentially doesn’t overheat.  It maintains its internal temperature and stays very stable internally.

In volume for volume, flexible wood fibre stores about 12 times more heat than fibreglass and rigid wood fibre boards store about 12 times more heat than PIR, and around 15 times more heat than EPS. So again, on every metric the wood fibre is outperforming the synthetic materials.  This creates buildings that are very stable in the summer.  You’re reducing your overheating risk, so you’re making the building much safer for occupants.  Also that heat absorption lowers heat demand.  It can absorb heat during the day and slowly release it during the evening, so again it’s keeping the internal environment much more stable.  It’s ability to manage moisture also preserves timber, so wood fibre is able to buffer humidity in walls and even out humidity so that you don’t get accumulations in existing timber.  It prevents mould growth and it enables safe refurbishment of building.

Finally, whilst wood fibre naturally contains formaldehyde, something you can’t take out of it, it comes from the wood itself, it gives off very few VOCs.  When you combine that with its ability to buffer moisture, it has a really beneficial effect on indoor air quality which again makes the internal environment very, very healthy for its occupants.

Hopefully that gives you some new insight into wood fibre insulation and what it can do.  If you have any other questions about wood fibre insulation or other sustainable building materials, please feel free to email me at Chris@backtoearth or alternatively give me a ring on 01392 861763.

The post Wood fibre insulation 101 appeared first on Fibres.

Roof & floor insulation, fixing fixtures & fittings and renders

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We’ve developed the first free, online wood fibre insulation course. Designed for architects, builders and self-builders, the course covers how to specify, source and use wood fibre effectively.

If you’re working on a building project and need help specifying your materials, checkout the following.

Hello and welcome to this week’s ‘Back to Earth’ podcast, with me, Chris Brookman.

This is a show for building professionals and self-builders, all about the use of sustainable building materials.

This week we have three or maybe four main areas of questions.  We’ve had quite a few enquiries about roof insulation this week.  We have a load of enquiries about a floor construction without using concrete.  We’ve got enquiries about fixing fixtures and fittings to walls after they’ve been insulated and then we’ve got a load of questions about render and what they can be applied to, how you care for them, how long it takes to dry and how you clean them.

So starting with the roof structure. This is quite an interesting one actually, this one.  This is an outdoor farm building that’s basically being converted into a hot tub and sauna room, which is not one that I’ve covered before.  Perfectly possible using wood fibre.  Actually, really, really good because wood fibre’s really good with moisture, but the absolutely critical thing because you’ve got a sauna inside – which is obviously very, very warm and moist – it’s absolutely critical to get your vapour control layer installed absolutely perfectly to make sure you don’t get moisture leaking through from the interior of the building and obviously escaping out into the insulation during the winter.  That obviously would be a problem. So absolutely critical on the vapour control layer.

The rest of the installation for a roof structure using wood fibre; very simply, flexible wood fibre between the rafters. In this particular case we’ve got 150ml between the rafters, 100ml on top of the rafters in the form of a wood fibre board, the UD top board, and then it would be counter battened, battened and slated. Really, really good from a thermal mass point of view and acoustic point of view, so it’s going to be very quiet in there, but yeah, as I say, really important on the vapour control side to get that right.

The other project that we’ve been looking at particularly was a flat roof construction. Now, flat roofs generally people assume – wrongly unfortunately – that the wood fibre can’t be used in an unvented flat roof situation.  But actually it can – and it’s actually really, really useful in that scenario because it can be used in between your joists which normally that area wouldn’t be used by insulation.

So a normal build up would be – starting on the inside, you’d have your plasterboard finish. The critical component to the whole thing is a variable vapour control layer. Now there’s lots on the market. We supply one called Udi Steam 10 Plus, which is one from Unger Diffutherm but equally there’s Pro Cleamer and there’s a whole load of different ones on the market.  They all do a pretty similar job, but they are absolutely vital to the functioning of that flat roof.

So essentially in the winter months the membrane stays very vapour tight and prevents most of the moisture from leaking up into the roof, but obviously over a period of time you do get small amounts actually condensing in the roof structure and in the insulation.  That’s fine. So long as it keeps within a certain level the wood fibre is really easily able to cope with small amounts of moisture.

And then generally in the summer, the roof structure heats up and all of that moisture is actually driven towards the interior. Now, the vapour control layer – because it’s variable – what it allows you to do is the membrane opens up and allows that moisture to come back into the interior of the building and allows the roof to dry out completely before everything cools down again and you go through another winter. So it’s absolutely critical to the functioning of that roof.

Once you’ve got that membrane in, you have your insulation between your joists, as I said. If you need to, you can have a layer of sarking board on top of the joists to reduce thermal bridging. Then you have your ply deck and single ply membrane or GRP, whichever you’re using for your finish.  A really, really effective way to do a flat roof.

So, moving on to dry floor construction.  Normally when you’re building a solid floor you have a layer of hard core, you’ve got a layer of concrete and then you put your insulation in and then all your floor finishes. With all that moisture, that moisture’s got to go somewhere and if you’re dealing with a very moisture sensitive building, like a church in this particular case, the last thing you want to do is chuck a load of moisture in the bottom of it, which has then got to come out through sensitive stonework normally. 

So with the particular system that we generally recommend, there is absolutely concrete in the floor, it’s very quick to install and, as I say, it’s dry – so as soon as you’ve got everything in place, you can turn the heating on, you can finish the floor and you’re done.

Now the floor normally starts with a layer of what’s called foam glass, and there’s lots of different products on the market.  There’s one called TECHNOpore. There’s Glypore, there’s lots of different pores! They’re all essentially foamed recycled glass and then broken up into an aggregate, so they’re normally either a 25ml or a 50ml aggregate.  That’s poured straight down onto – it can be poured onto a damp membrane or just a geotextile, whichever, but it’s basically put straight onto the ground and then you use a plate compactor to compact it in.  It’s actually quite difficult to get completely level, so on top of that we normally recommend a geotextile and then with a layer of either very, very coarse sand or something like 10ml stone chippings over the top of that geotextile so that you can screed that layer completely flat and then you’ve got a dead flat surface to come up off.

So once that’s in place you put a 22ml wood fibre layer over the top. We normally recommend the Udi top board.  It’s a 280 kpa board, so it’s a really strong, very high density board.  Once that’s in place, then our 45ml lithotherm tiles go over the top. Now they’re basically a screed replacement. Very high density tile that interlocks. So it’s got a tongue and groove profile on it and it allows you to layer a dry, very high density layer with grooves in it, to take pipes.  So once all the tiles are in, you can lay your pipes. Use a bit of dry mix screed around the ends of the pipes and then you have a finished surface that you can tile onto or you can put your floorboards onto. That’s basically what we’re doing in this project.  This project’s for a church in south-west London and that way they’re not going to add any moisture to the building. They can quickly get that floor in and as soon as it’s down they’ve got a very high compressive strength floor that they can actually use scissor jacks and all sorts on.

Moving on to how to fix fixtures and fittings to insulated surfaces. One particular question that we’ve had has been about you how you fit reasonably heavy radiators to internal wall insulation once it’s been installed. 

So there are lots of ways. You can install timber batons into the wall before you put your wood fibre boards on, but to be fair that’s a bit of a faff.  Generally, the best way to do it is to forget about where the radiator’s actually going to go, put all your insulation in and then we do a fixing from Fisher called Thermax, which is basically a massive screw and a massive Rawlplug that is drilled into the wall. The screw screws into the Rawlplug and then on the end of it is a big thermally broken plastic head, so that decouples anything that you fix into that head from the main shaft at the fixing. You finish that plastic head flush with the surface of the wall and then you can screw your radiator bracket into those points. Really, really simple and they come from anything between 80 up to about 200ml long, so irrespective of whatever depth of insulation you’re using, there’s normally a fixing for it.

And then the final area that we’ve been working on this week is renders and as it’s getting towards the end of the year, people are becoming very conscious of drying times and also what the weather’s like with regard to whether finishes are going to dry or not.

Our main topic of conversation has been what’s the setting time of renders? For most of the Baumit renders, certainly the external ones, they will typically set overnight, but you do need to leave it at least 1mm a day to cure before you put any finishes on it.  If you’re using MP69 you want to be leaving 16 to 18 days really to let it cure before you put your finish on. When you’re using things like MT55 onto either render boards or whatever, then again you want to leave it for the best part of a week to cure.

With regard to the finishes though, Baumit do an accelerator for their silicon finishes, so if you are using any of the Baumit silicon top products and it is getting on to autumn, then the speed top is a 250ml bottle of additive that you add to each tub and it will guarantee that it will set in about six to eight hours.  So should you be using anything at this time of year and it’s cold and damp, then that’s a great way to make sure that you can get it on the wall and get it set.

And the final question regarding the renders has been about what do you with renders that have got discoloured? We’ve got one particular project where a gutter had broken, got a load of water running down the wall regularly and basically bringing all the muck out of the gutter with it.

The best thing to do really is to give a gentle pressure wash. You can gently pressure wash silicon renders as long as you keep about a foot away from the wall or so with the head of the pressure washer. Then there are various render cleaners on the market. Baumit do one, but equally plenty of other manufacturer’s do. They’re largely just strong soaps, and if that doesn’t work normally the best thing if it’s just spot discolouration you can actually just get a tub of the original render, stir it up, get a paint brush and dab the paint brush into it and actually stipple it into the surface of the render. That will obviously cover up any stains. Where you don’t have any render left over, then the next best thing is to use the silicon paint that goes over the top.

So that concludes this week’s show. If you have any further questions about sustainable building materials, please feel free to email me at [email protected] or alternatively give me a ring on 01392 861763.

Check out our next show this time next week.

Thanks for listening!

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