I am really, really, REALLY disappointed to be writing this article. I had hoped that with the official launch of the Green Guide to Specification the environmental battle between timber and PVC-U windows would be over and we would all concentrate on more important matters, such as surviving in the current depressed market, such as coping with the revisions to Building Regulations and such as learning about the upcoming Building Research Establishment scheme for the Responsible Sourcing of Materials. We have revisions to British Standards for the performance of windows and doors (BS 6375 Parts 1 and 2 and the new Part 3) on the way. We will have CE Marking before too long. I could go on. All these will affect windows and doorsets of any framing material so they are all things we would do better to address as an industry

Then I see an advertisement from the Wood Window Alliance which can only be described as confusing. In big letters we have “Wood A, Plastic D, Aluminium D^” with reference to the BRE Green Guide. The little up arrow indicates the small print lower down “Climate Change Indicator ratings for domestic wood, PVC-U and powder coated aluminium windows”. Now this is factually true but it is only one part of the story. I’ll try and explain. All building products have environmental impacts of various different kinds. The BRE Green Guide identifies thirteen impact categories and it measures each product against each category. A panel of interested parties and experts were consulted to rank the importance of each category and weightings applied to each one before a summary rating is arrived at. The table shows the thirteen impact categories and the ratings of painted timber and PVC-U for each of them. So, yes, timber rates A for climate change and PVC-U is rated D. But look at stratospheric ozone depletion for example – PVC-U ranks B and timber ranks E. Browse down the list and you will see no one material is better in all categories. And then look at the top two rows in red where the summary ratings for domestic and commercial windows are and what do you see? PVC-U and painted wood windows get the same rating! The overall environmental impact of the two products is the same.

To make things a little more complicated these are not the same ratings that were on the BRE Green Guide web site previously, so I hope they haven’t changed again in the period since I wrote this article. The point is that there is no clear winner in environmental terms between the two materials. This is no surprise as this has been the conclusion from numerous life cycle analyses over the years. The most important thing for windows is their in use phase which the Green Guide does not address. Here’s what the Green Guide web site (go to http://www.thegreenguide.org.uk/, register and have a look)  states:

“The main environmental impact of windows is from the heat loss through them. Attention is drawn to the large number of credits available in BREEAM, the Code for Sustainable Homes and EcoHomes for reducing fabric heat loss and improving operational CO2 emissions compared to the small number available for materials specification. The embodied impact of windows should only be taken into account as a small part of the decision, with the main emphasis being to choose a window which will reduce operational energy usage.

Windows are one of the elements with a less important role in the overall embodied impact of buildings due to their low impacts and low area within buildings…”

It’s important that we ensure that our windows, regardless of framing material, are energy efficient. As an industry we need to ensure that regulators don’t get distracted by low U values without considering the effect of the reduction in solar gain that occurs when you make windows with ever lower U values. The Standard Assessment Procedure (SAP) for calculating Dwelling Emission Rates (DERs) includes solar gain but still many specifiers and procurers equate low U value with better performance and forget to consider solar gain. In fact, most of the benefit of low U values is lost by lower solar gains. And when you move to U values below about 1.3 you need triple glazing which increases cost disproportionately for a marginal decrease in U value. I wrote about this tipping point last month. If we are to avoid unnecessary cost and weight burdens on our products, we need to work together as an industry to promote Window Energy Ratings for the domestic replacement market as well as ensuring that the underlying data behind WERs is recognised and used in the SAP calculations. Counted today, there are 161 A Rated windows. Wood and aluminium windows are there but the majority (94%) are PVC-U. There also lots of windows rated C or better (got bored counting those and gave up) which is higher than current Building Regulation requirements and which qualifies for Energy Saving Recommended status from the Energy Saving Trust.

As an industry, we have a good tale to tell. We can produce high quality, energy efficient windows that help towards lowering CO2 emissions. We can all help improve the environmental performance of our buildings cost-effectively so let’s concentrate on that. Let consumers decide what material they want their frames made from without making confusing environmental claims that detract from the message that it is thermal performance that matters.