Timber, PVC & Aluminium Window Frames – Sustainability

Double Glazing Window Frames - Heat Loss in Use

Heat lost through the double glazed window frame when in use is likely to have a far greater environmental impact than any impact generated in its production.
It is therefore important to choose a window frame material that has the least conductivity. Wood is the least conductive material used in double glazed window profiles, followed by PVC and then aluminium

Timber Double Glazing Window Frames - Environmental Impact

The choice of timber, its treatment and maintenance are crucial in reducing a double glazing window frame's environmental impact. Specific sustainability considerations when selecting timber double glazing window frames:-

• Specify FSC sourced timber for use in the window frame.
  
• Whether specifying hardwood or softwood timber for the window frame, exclude the use of sapwood.
  
• Painting wood adds significantly to a timber window frame’s environmental impact. Either specify naturally durable timber that doesn’t need treating, or select a timber window frame treatment with low environmental impact.
  
• If the timber for the window frame needs treating, have this done at the factory. Factory painting of timber double glazing frames can double the period before repaint is required.
  
• Double glazed windows should be as large as practically possible. Even with wooden frames, the metal spacers between the glazing panes act as cold bridges. Large panes have less perimeter length than lots of smaller panes.

PVC & Aluminium Double Glazing Frames - Recycled Content

The overall environmental impact of Aluminium and PVC window frames can be substantially reduced by improving the quantity of recycled material content in the frames. Both Aluminium and PVC have significant environmental impacts throughout their production phases. This is especially so in their use of non-renewable resources, energy use and toxic bi-products.

At present, PVC double glazed window frames contain little or no recycled content. The PVC industry is committed to improve this situation by 2010. By 2005 the PVC industry was committed to recycling 50% of post consumer PVC windows. The PVC industry has yet to verify whether or not this has been achieved.

Aluminium double glazed window frames do now contain some recycled material. The amounts can vary considerably between double glazing frame manufacturers.

Sustainability – Choice of Timber or PVC Double Glazed Window Frames

Around half the double glazed windows installed in the UK have PVC frames. There is no clear agreement on the environmental preference of timber or PVC for use in double glazed window frames. The prime concern with PVC window frames is the environmental impact of their production. There is no clear consensus on whether timber or PVC has a clear advantage in terms of sustainability.
The current low levels of recycled material used in the manufacture of PVC window frames is an environmental drawback. Careful specification of the timber used for window frames and the associated treatment of the timber are very influential. These considerations probably indicate that timber is the more environmentally considerate material to use for double glazed window and door profiles.

Timber / Aluminium Composite Double Glazed Window Frames

In this composite, the timber is faced with aluminium. The need to coat timber with synthetic paints is counterbalanced by the cladding of the timber section with the very much more durable aluminium. The high environmental impact of aluminium is balanced out by the seriously reduced volume of aluminium used in the window frame. The position is further improved if more recycled aluminium is used in the window frame cladding.
Aluminium clad timber window frames are a recent innovation but their lifetime is expected to be over 40 years, compared with that of PVC window frames, which is around 25 years.

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Double Glazed Window & Door Frames – Sustainability Considerations for PVC Aluminium and Timber.

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