At the time of writing this article, the Building Research Establishment (BRE) have issued interim ratings for windows for their Green Guide to Specification. You may recall that these ratings use an A+ to E ratings with, unsurprisingly, A+ being the best and E the worst. There are some very strange ratings given but as they are interim, I cannot tell you what these are just yet. This Green Guide rating system covers what is termed cradle to gate, i.e., the use phase of products is not considered (although the life expectancy is). It uses Building Regulation maximum U values for the performance of all windows. This causes a strange anomaly. In houses, where most heat is lost through windows, the in-use phase of those windows has far more environmental impact than the manufacture phase. For new build, this is taken into account at the design stage using the Standard Assessment Procedure (SAP) using U values to assess heat loss and g values to assess solar gain. The Code for Sustainable Homes (CSH) requires reducing levels of CO2 emissions at different levels within the code but, and it’s a big but, it also requires some construction materials to achieve certain ratings from the Green Guide in order to score points. This is where the problem arises. Suppose that a window rated E by BRE in the Green Guide gets an A rating by the British Fenestration Rating Council (BFRC) which takes into account U and g values as well as air leakage. Over the whole life of the window this particular product could be much more environmentally beneficial than a window rated A+ by the Green Guide but only rated E by BFRC. The current system in the Code could exclude the better window being used. Neither the Green Guide nor the Code in the materials section recognise this.

I know the existence of two rating systems is confusing and I hope you can see where I’m coming from.

We have made representation to BRE on this and hope that the Window Energy Ratings can be taken into account at some stage, possibly next year.

This situation is indicative of the muddled thinking surrounding energy efficient windows. A paper published by the Department for Communities and Local Government, about which I wrote a couple of months ago, is suggesting that lower U values will be needed for future windows with no account taken of the overall energy balance of a window. SAP for new build evens things out as g value is included but the inevitable consequence is that these very low U value windows, 0.7 has been suggested as may be necessary for new houses, will then form part of the requirements for replacement windows where g values are not included. So, new build is sorted by SAP and the thermal performance of them will improve in stages before we see zero carbon new homes in 2016, and ultra low U value windows will not be mandatory and may not be necessary. However, 80% of the houses that will exist by 2050 have already been built according to figures I have seen. If windows are replaced in them with very low U values, then we could be worsening the overall energy performance of the windows. The use of Window Energy Ratings would prevent that.

Let’s assume that as an industry we can convince government to use WERs for the replacement sector, what then is the incentive for the householder to buy energy efficient windows? The Energy Savings Trust have awarded their Energy Savings Recommended (ESR) certificates to windows with a WER of Band C or better and no doubt some householders will see the sense in paying a little extra for them. (I’m told not to be so naïve when I say that. Householders will NOT pay extra, it is said). I won’t rehearse the campaign to get VAT reduced on ESR windows except to note that the chances of this ever happening are remote. What other incentives could be given? Suggestions include a reduction in council tax for energy efficient homes based on the Energy Performance Certificates now necessary for houses that are sold or let. Who would fund that? Local authorities? If so, they would have to increase Council Tax on less energy efficient homes to maintain their income levels to the disadvantage of poorer homes who cannot afford the thermal improvements. What about people like me who have double glazed windows that are over 20 years old with “standard” double glazing of 4x20x4mm? The frames and hardware are fine with no need for replacement, and no IGUs have failed, so what incentive is there for me to replace the sealed units with energy efficient ones with a low centre pane U value – triple glazed, low iron, low e, gas filled, and a good g value? There are incentives to increase the thickness of my loft insulation or to have cavity wall insulation installed (indeed, I’ve done exactly that), but so much is heat is lost through glazing in existing dwellings that it’s criminal not to address it.

A speaker at a recent conference from the Department of Business, Enterprise and Regulatory Reform, formerly part of DTI, spoke of their Sustainable Construction Strategy and he recognised that charging VAT at 5% on fuel and 17.5% on energy efficient windows was somewhat contradictory, but they are not the decision makers in this. Al they can do is try and persuade the Treasury in this. He did not seem overly optimistic!

It’s all what my Gran used to call a Bugger’s Muddle. Every government department, it seems, has its own sustainable construction policy, sometimes in agreement, sometimes conflicting, but one of the major sources of heat loss – glazing – is not being effectively addressed. In new build, the CSH requirements for materials have a potentially negative effect by imposing minimum Green Guide ratings for building products that may not be the best over the life of the building, and for replacements, no incentives at all for fitting energy efficient windows or upgrading to energy efficient IGUs. The solutions don’t seem to hard to spot. The Green Guide should be amended to take into account the in-use phase, or the Code for Sustainable Homes should have the materials section amended so that windows can have a lower Green Guide rating so long as they have a higher Window Energy Rating, and VAT on energy efficient replacement windows or replacement IGUs should be reduced.

Any bets on any of this happening?

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