As always, This article is a thnk piece, something to stir you into researching some of the points I raise here, to add to your own Knowledge Bank

Windows and doors offer access through an external wall for two distinct reasons, For Windows, it is light, ventilation and the possibility of access; for Doors, it is simple access for people and goods to the interior of the building, with the possibility of light.

Windows

A window’s primary function is to let in not only light, but also ventilation, and sometimes allow access. it’s an opening punched through the external fabric to let in light and often add ventilation; from the internal living room in a domestic house, its a picture frame; in a church, it’s a storyboard; in a bank, is a security problem. in a shop, it’s a display. But for many its a sound problem.

But all have one thing in common, it’s a break in the weather lining that needs to be sealed, and so many times I see it done Badley, often misusing materials that have a short shelf life, and are so often applied or installed wrong.

Windows across the broad spectrum of buildings come in many designs, from stone to timber and recently plastic. The latter trying to replace timber, that needed painting, and servicing, to metal.

Metal can be seen on both domestic, and commercial buildings, the latter as curtain walling, large metal mullions spanning many floors to hold acres of glass into place.

Glass has also undergone a huge evolution, from the bulls eye square glass panes to large triple or quadruple glass panels held in place with metal brackets and cover plate, tinted to reflect solar gain or for Architectural appearance.

Weather proofing for the commercial building is simply the glass and metal, often there is no other material involved but on domestic buildings brickwork and other claddings are involved complicating the detailing.

In recent years timber has undergone a transformation, cheap timber that was never suited to window manufacture, and relied on paint to protect it, and bad detailing of the window interface to the brickwork, released its hold on the market, to UVPC windows, that offered both longevity and easy installation both for new build and the renovation market, offering a no paint solution, and double or triple glasing.

But The clever use of multiple timbers laminiated together with more durable timber to the exterior, and softer often less durable timber in the core away from the weather, and often treated to give a little more protection, are transforming the window market.

Timber can be repaired, but UVPC is almost impossible to repair, yes it offers a thermal performance, but new designs in timber window, now can compete.

Ventilation is one of the endering factors of any window, the ability to poen part of all of the window, to allow fresh air. There are three ways this can be acgieved, opening out, opening in ot sliding.

The opening out detail is predominately the way many English windows work, the natural tendency for the weather to drain down the external surface, and away is protected by overlapping surfaces, but on the European continent windows tend to open inwards, and there is a very good reason for this, the weather is often a lot warmer, and shutters have been the main stay in protecting the interior from the harsh sun, preventing the outward opening of windows, but an inward opening window allowed the shutter to remain closed, and still allow windows to open and ventilate the room.

Sliding sash windows did much the same and were the alternative method of using shutters in the UK, and still allow ventilation. The beauty of the shutter is that the top and bottom panels could be slid open slightly allowing hot air to ventilate at the top, and cool air to flow into the room at the bottom. Control of the flow was a simple opening or closing of the gap offering a lot more control. This is discussed later in this section.

The development of the internal shutter for more grander homes was seen as a more elegant design but defeated the beauty of the external shutter that shaded the heat external not internally where it was too late, the heat already being inside the room.

Which ever design is used, placing the window as near to the external surface helped to keep the weather away from the internal surface, but offered a difficult detail. Older building moved the window back slightly and covered part of the frame with the outer skin of brickwork of a 229 brick, solid wall, not perfect, but far better than the detail to come.

The mass building of houses after the second world war, and the need to simplicity, did away with this and relied on a flush opening, the frame push as far out as possible and sealed with paint or a drip channel in the frame. Not a good detail and open to failure.

The Sash window was and still is the ultimate window design, easy to use and install, easily repaired, and in many cases provided a large opening when the panels were removed to move furniture into the building, even to upper rooms. It utilised the use of the outer skin of brickwork to seal the window and its modular design enabled easy repair.

The cavity wall, and the inclusion of cavity wall insulation and the avoidance of cold bridging, now opens up the ability to return to the use of the eternal skin to become part of the detail once again. By closing the cavity with a insulated cavity barrier, also achieving the required fire seal, and reducing the cold bridge to a minimum.

The cill is a major part of the design of any window, old or new, it sheds water thar will inevitably drain down the impermeable glass, and allow it to drip away from the wall and not cultivate mould or staining of the brickwork or cladding below. The cill should extend either side to form horns, preferably 50mm, to allow water to dissipate correctly and not to collect at the edge and cause a large drip. An alternative is to raise the edge of the cill slightly an prevent this, but it’s not as effective as the use of the cill being extended. The body of the cill should overhang the main wall by 50mm also, to prevent water stain or mold growth.

The use of correctly applied seals and drips to the frame will prevent a major cause of failure, that of capillary action, the ability of water to cling to a surface and travel along that surface, and if it collided with another hard surface, climb upwards and caused havoc. The use of rubber seals set into the frame sealing the gaps between the frames helps the drip, routed into the frame, seal against capillary action and wind blown rain creeping into the building.

The sequence of operations, is a fundamental part of any detail, understanding how a detail is constructed, for a window with a timber cill only, the horns or extensions of the timber cill are slid into a area cut away from the first brick course of the window reviel, and bedded in mortar. If the window is designed to hide behind the outer skin, then it needs to be fed in from the internal side of the wall, taking great car not to disturb the brick or joint.

Fixing should never be left to site, all details need adequate restraint, and for a timber window being installed into a cavity situation, a stainless-steel bracket should be fixed to the timber frame prior to installation together with an expanding seal to prevent water and wind ingress through the joint, set into a small rebate in the timber. The bracket may be fixed in the end of the internal block or taken round to the internal face which ever gives the greatest security or easy of fixing.

As the brickwork will be installed way before any window frame, the window manufacturer will require the structural opening, so the frame may be made slightly smaller to aid installation, the use of spacer blocks or as per the frame detail here, a cranked fixing bracket may be used, with a fixing to the internal face, giving a more flexible alinement when a elongated hole in the bracket is used.

A window is no more than an opening through a wall, behind that simple statement lies a world of technical problems. The creation of an opening in the external wall creates the first of many problem, the first being support of the external material over the opening.

This is done via several methods, the arch, and there are many shapes and styles to choose from, and the flat lintel. But primarily the steel lintel.

Although the window’s primary role might be light, in some buildings such as churches, it was often used as a storyboard and the use of stained glass set into a lead frame to depict passages from the bible, or in a stately home, the union of two heraldic coats of arms.

The next problem is the hole you are making by piercing a hole through the weathering. Creates a problem of continuity, the detail between the window and external skin needs to join the two often different materials together and continue the weather protection, which is not an easy feat and one that often fails.

Detailing the interface between window, or door, requires an understanding of how water, air, dust, insects, and fire can be resisted.

Older Victorian and later Edwardian buildings did this by hiding the window behind the outer external skin of brickwork. Which also solved the problem of securing the window to the brickwork. This worked well to hide the weight chamber of the sash window.

Glass is not porous, its sheds almost as much as the rain that lands upon it; therefore the cill is the next big portion of the detail to be looked at.

Is the cill big enough to shed the water away adequately, is there a sufficiently large drip on the the underside? As stated above the cill should extend 45 - 50mm beyond the face of the wall.

The development of glass, plays an important role in the development of, and use of windows, from castle windows often with no glass, and therefore small, thin openings.

The manufacture of glass was originally a large blob of molten glass on the end of an iron rod, which was spun to produce a disk of glass that could be cut into small squares. the centre was not wasted; it became the bullseye, so often seen in doors and windows with a Edwardian frame.

In hot countries, the window created another problem that of solar gain, and the creation of external shutters, often louvred to allow some ventilation, and a variety of opening methods, In France, the use use of external shutters meant the use of windows that opened internally.

In England, the use of internal shutters gave rise to the sash window and vertical sliding frames, often seen as the perfect means of ventilation control.

In General, Shutters, whether internal or external, increased the security of house windows, A recent development has been the integration of a roller shutter into the steel lintel, opened internally via a winder offering increased security and some form of automation when a small electric motor os fitted with sensors to aid security.

The mass building rise in the UK resulted in the use of window frames with side openings and top-hung frames, the arrow of the dotted line denotes the opening side, although adding a thick line denotes the hinge position.

Timber - UPVC Metal

In this author’s training, timber was the predominant frame material, Metal was used in specific areas, and UPVC was not yet used, but come the late 70’s early 80’s the popularity of UPVC became the main material used, Timber with is poor record of decay, and constant need for painting, plus its leaky nature in terms of wind ingress , allowed UPVC to dominate, no need for paining, a sealed interface between the opening leaf and main frame reducing to almost till the air ingress, and of course noise.

But UPVC is not sustainable, and timber, with better use of laminated timber and better detailing, has made a comeback. With the use of more durable timber to the exterior and cheaper but still durable timber to the interior as a laminate and the use of extruded aluminium is providing secure, stronger more durable windows with low maintenance.

Better-designed hinges that throw the window away from the frame and locks that secure on all four corners.

Open in out or sliding sash

Thought Europe there are roughly three types of window opening direction, In the UK opening out are predominant, with Sliding Sash holding onto a sizeable share , but in Europe windows open predominately into the room, The direction of use is controlled by the use of shutters, to aid in shading the room and still maintain ventilation

Shading

The orientation of a building is fundamental to the path of the sun from sun rise to sun set, for any day of the year never being the same, each day is slightly different from the day before or after. Up until recently, calculating the sun path analysis for and buildng and incorporating the neighbouring buildings into the scenario, was complex and very time consuming, just for one day yet alone a full year, but most CAD programs can do this in a moment, giving the designer not only the external shading, but also how the sun and possibly shading will affect the internal space.

Orientation

The suns path is predictable, its angle from sun rise to sun set is is built in to almost every 3D CAD program, so the orientation of the building to obtain the best solar exposure is not as difficult as it once was.

Its Planning’s job to control how a building looks and it’s fit into the surrounding landscape, but there is a conflict between the correct orientation in relation to the sun, its relation to the other buildings and the energy efficiency to cool or shade the building effectively.

Weathering

Water in the form of rain will travel between the main frame and the hinged opening frame in the form of Capillary Action. To stop this, drips in the form of a small routed grove are placed to break the capillary action, Rubber draught seals are often added to act as seals to the wind blowing through the frame gap.

Around the main frame, a grove is added to take a mastic seal, often a sponge rod that will be squeezed and placed in the external grove of the frame. Often coated in mastic, they try to return to there original size and seal the gap against the frame and structure.

Adding drips to the head and cill frame will shed water away from exposed joints. The cill detail using a drip will make water flowing down the glass drip away from the facing brickwork and help prevent mould.

Fixing doors and windows is so often achieved by three of more fixings through the side mullion into the brickwork or cladding.

So detailing any window requires a detail that shows all the materials that will interact with the window to determine the best fixing and sealing.

It’s not unusual to use brackets to secure the window frame to an inner leaf, either because the outer frame is not sufficiently strong or the window frame detailing or drips do not allow. So a metal bracket is used to secure it to the inner leaf.

The use of a vapour barrier on the internal surface is a detail that needs careful handling to ensure a leak-free seal to the window frame is achieved to prevent vapour from leaking into the cavity insulation.

Securing the Window in place

Often left to the window company fitters, a little time in detailing how and into what will the window be secured. So often the simplest method might be a screw through the jamb into the external skin, but so often this might be that the cavity barrier, a simple alternative is to prefix a securing bracket to the Jamb, facing back into the inside elevation, allowing a fixing to the inner skin or block or timber / Metal stud.

Daylight Factor

A major factor of any window is to admit daylight through the opening, for domestic, the volume of light is controlled by the size, and shape of the opening, together with the type of glass used. In Chapter 19 Glass its history and use, right up to modern day and beyond into the future is discussed.

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