The current choice of material for windows and doors, in probable order of popularity, is PVCu, aluminium, solid wood, engineered wood and steel. But which, if any, is a genuinely eco friendly option?
It has to be said that steel has little to recommend it. Its thermal performance is poor, the cost high and it is highmaintenance. Unless there is a structural need, there is always a better alternative. Similarly with aluminium. Although it is a recyclable material, in its powder-coated form (usual for windows and doors) it is practically non-recyclable due to problems in getting the coating off.
For the past 30 years PVCu has been the standard as it offers a relatively cheap product that is perceived to be long-life and maintenance-free. But the environmental impact of PVCu is controversial. The two camps, being environmentalists and the PVCu manufacturing industry, unsurprisingly take widely different views. To try and put the argument in a nutshell:
- PVCu uses large amounts of fossil fuel (worldwide production of PVCu is currently around 18 million tonnes per year, about 57% of which is oil, as a raw material). It also uses large amounts of chemical additives. There seems to be no argument about how PVCu is produced — it is a question of the quantity of by-products and waste produced and how toxic it is.
- The Building Research Establishment has recently accepted that PVCu is a recyclable material. However, there are no post-consumer PVCu recycling facilities in the UK. Therefore it can only go to landfill.
- PVCu is said to be long-life and maintenance-free. There are paints designed to block UV light, preventing discolouration and extending the product’s life. But a cynic might ask why this is necessary if the product is indeed long-life and maintenance-free?
It perhaps comes as no surprise that the only real eco option is wood. In the past wood has had something of a bad press: said to be expensive, to warp, rot, and need lots of maintenance. But modern manufacturing methods mean that none of this is necessarily true.
Eco windows and doors are generally made from durable timber: Douglas fir, redwood or oak. The ones with true eco credentials are Forestry Stewardship Council certified, meaning that the timber comes from responsibly managed forests. Whether they are solid timber or engineered timber, they tend to not twist or warp (engineered timber being especially good in this respect) and modern design and manufacturing methods mean that rain water is conducted away, preventing rot.
Eco windows are treated with non-toxic compounds to prevent fungal or insect attack. In addition, paint or stain finishes are also organic or water based. This means that at the end of the window’s life it can be composted as there are no chemicals in the wood.
The performance of timber windows and doors is at least as good as PVCu. On average you might expect a U-value of around 1.2W/m² from a timber window compared to a PVCu standard of 1.8W/m².
The maintenance required is not what it was either. Modern micro-porous paints and stains are actually absorbed by the wood so that they don’t blister or flake. They do require maintenance but this generally amounts to wiping clean and applying a single coat of paint or stain once every five or six years.
The argument that wood does not last as long is also countered with many companies offering 30-year guarantees against rot. Add that to timber’s fair prices, and it seems that choosing eco-friendly means no more than questioning conventional wisdom. Does green cost more?
Good quality wooden windows from a major manufacturer will vary from £250/m² for standard windows to £600/m² for windows of the ‘Passivhaus’ standard. Solid timber windows from your local joiner might cost £200 to £500/m2 and PVCu £200 to £350/m². It is quite likely that wood – engineered or solid – will cost more, but perhaps not as much as you might think.
To quote Dr Gillian Menzies of Heriot Watt University: “To build sustainably, we are not required to sacrifice comfort and wellbeing, but to act responsibly in the way we select materials and design components for construction.”