Window frame

Selecting the quality of window frame.

A window frame does not form part of a double glazing window .

Rather, the double glazing window is positioned within a frame. Care should be taken in selecting the quality of window frame used as it will affect the insulation properties of a double glazing window by up to 30% and thus its double glazing window Energy Rating. The most widely used frame materials are timber, aluminium and PVC (a plastic derivative). Under Document L specifications, all new or replacement windows (including frames and double glazing window) should have a U value of no higher than 2.0 W/m 2K.

Strong, secure and long-life window frames.

Aluminium double glazing window frames, popular in the 1960’s and 1970’s, are now less widely used due to their relatively high cost and poor insulation properties. When aluminium is used, a thermal break between the frame and the double glazing window will help to improve the window’s energy rating.

Aluminium frames do however have some advantages as they are strong, secure, require very little maintenance and have a long life expectancy. Metal frames also resist expansion - so they are suitable for situations with strong sunlight or very damp weather.).

Durable and excellent insulators for windows.

Timber frames are made from varieties of hardwood (from deciduous trees). Durable and attractive, timber frames give homes a traditional look and feel. They do, however, require more dedicated maintenance and are more expensive.
The most commonly used timber for frames comes from tropical mahoganies, such as meranti. European hardwoods such as oak, beech and ash are more costly but do have a finer finish and greater resilience. Usually timber frames should be stained or varnished rather than painted, but recommended treatments depend on the variety of wood.

A key point to check when purchasing timber frames is that the wood has been properly dried, to avoid future problems of cracking or shrinking. The thickness, grain and straightness of the wood to be used also need to be taken into account, as these will affect the double glazing window’s strength and resistance to distortion.

Timber frames are excellent insulators as they are low thermal conductors. Document L requires that new wood-framed windows should not have a U value higher than 2.0 W/m2K but exceptions are made for those used in historic buildings.

Maintenance free frames.

The most widely used material for window frames in recent years is hard PVC (sometimes referred to as PVC-U or UPVC). PVC frames are usually the lowest cost option, yet they provide excellent insulation and require little or no maintenance. White PVC is no longer the only option and a variety of different colours and finishes can be found, including ‘woodgrain’.

PVC frames are not as strong as metal or wood frames and can suffer from expansion under strong sunlight. When extra resistance is needed they can be reinforced with galvanised steel but this will reduce the double glazing window’s thermal efficiency.

Today, a home improvment project is the replacement of standard windows with more modern double glazing window. Some of the advantages to this are that they are less susceptible to condensation on the windows; they are more energy efficient, cutting down on high heating costs.

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