As we look more closely at the details of the Part L consultation, we are starting to pick up points which may need further clarification.
Paragraph 4.19 of the Technical Guidance on Part L allows an exception from the requirement to provide full window energy ratings (WERs) or composite U-values where “Where windows, roof windows, rooflights or glazed doors have to be hand-made (e.g. to match existing retained windows a Window Energy Rating12 or composite U-value may not be available, it would be unreasonable to expect the necessary calculations to be done for a one-off unit. Only in such exceptional circumstances may the alternative standard of a centrepane U-value of 1.2 W/m2.K be accepted.”
We think “one-off” and “exceptional circumstances” need to be much more carefully defined. We foresee that many smaller manufacturers, who make bespoke windows which vary from building to building rather than standard designs, could consider that almost everything they make is ‘hand-made’ and therefore ‘one-off units’. They would therefore read this paragraph as effectively absolving them from having to obtain the detailed U-value calculations.
However, it could be read as saying that a one-off unit would be the replacement of a single window in an existing building to match the other windows in the property, but if all the windows were to be replaced, this would not qualify as ‘exceptional circumstances’ in these terms.
It’s easy to agree that that a new circular stained glass unit replacing the 400 year old one on the stairway of Crumbling Mansions made by a small specialist joinery manufacturer doesn’t need the full WER or calculation. But at what point does it become reasonable? If there were ten of them? If a manufacturer was doing a thousand such ‘bespoke’ windows a year?
We need to devise a wording that makes this clear and that will be acceptable to the majority of BWF members.