A few months ago, I wrote about the Code for Sustainable Homes published by the Government – “A step change in sustainable home building practice”. I’m sure you all have a copy of the Code by your bedside for those tricky nights when sleep is hard to come by, but should you have missed this you can download a copy from http://www.pauljervis.net/filemgmt/viewcat.php?cid=11&page=2. The original article about the code can be read on http://www.pauljervis.net/index.php?topic=Articles .

However, as it stands this 28 page Code is not sufficient to put the Government’s policy into action. To do that they need some technical guidance and this they have produced in a 213 page document, downloadable form this link http://www.pauljervis.net/filemgmt/viewcat.php?cid=11 (not recommended for the faint of heart, those with a non-technical disposition or those with a life). Government policy is that all new houses built using public money via the Housing Corporation and English Partnerships must comply with the Code, with minimum levels rising over time towards that almost mythical beast, carbon neutrality by 2016 (there are those who think this is completely impracticable, but I couldn’t possibly comment).

The system is quite complicated but I’ll try and distil the essence of it as far as windows and doors are concerned. There are six levels within the code, one star,«, to six stars, ««««««, based on a system of points being awarded for each item on a list of identified aspects. Each level has its own set of requirements and points allocations, with materials being but one element. Minimum standards are set at each level for energy performance, for which windows play an obviously important part, and water use. In addition, minimum standards are set for materials at entry level (i.e. the same minimum for each Code level). Points are given for the energy and water requirements at each level and additional points for other characteristics are needed to reach the total number of points required for each Code level (see Table 1).

Current opinion seems to suggest that Code level 3 is achievable using current building techniques but levels 4, 5 or 6 may prove extremely difficult to achieve. The Government is so confident that it can achieve Code level 6, our new (by the time you read this) Prime Minister has (re-)announced the building of exemplar schemes of zero carbon homes. He as also announced the reduction of stamp duty on zero carbon homes for a limited period (this could save £15,000 on houses above £500,000, which should be OK for terraced house purchasers in some of the housing hot spots of the South East).

As far as materials are concerned at least three of the following elements must be rated D or better in the revised BRE Green Guide : Roof structure and finishes; external walls; upper floor; internal walls; doors and windows. At the time of writing this article the revised ratings for doors and windows have yet to be published. The project of revising the Green Guide has proved more time-consuming than originally expected and there has been a slip of several months so far. However, it is hard to see how any window/door material will not achieve D or better so there is no reason why any material cannot be chosen and remember, only three out of the five aspects listed has to achieve any Green Guide rating at all.

Points are awarded for each of the elements being rated B or better (see table 2).

In addition, 0.3 to 1.8 points are available for responsible sourcing of the materials, e.g. by utilisation of Environmental Management Systems or by timber certification.

Originally, it was stated that A ratings would represent the best products on the market from a sustainability point of view, with A+ being reserved for any new products in the future that out-perform the current best. However, that seems to have gone by the board on the way and the portion of the revised Green Guide that has been published at the time of writing has quite a large number of A+ ratings. Perhaps we are going to have A++ and A+++ ratings that white goods have had to adopt.

The impact that the material from which windows and doors are made is therefore small compared to the effect the thermal performance of them could have on the points total of a house. The Code requires improved thermal performance of houses over 2006 Building Regulations Part L levels of performance, with points being awarded in the range 1.2 points, for performance 10% better than 2006 Part L, to 16.7 points for 100% better than 2006 Part L for aspects covered by building regulations (zero carbon covers domestic appliances as well). High performance doors and windows of whatever material have an important part to play in the overall thermal performance of the house, so let’s concentrate on improving the thermal performance of our products at a reasonable cost and not waste effort on irrelevant and frequently spurious knocking of framing materials.

As an indication of the relative importance of doors and windows, where a range of 0 to 0.9 points is available, up to 2.4 points are available for the provision of cycle storage, 1.2 for the provision of a space and services which allows the occupants to set up a home office in a quiet room, and up to 2.4 points for the provision of dedicated energy efficient light fittings. Therefore the design of the window and the selection of glazing is of far more import than dithering over material choice.

Sort of puts things into perspective, somehow.

Paul Jervis

May 2007