londonman said:freddymercurystwin said:True, but to be fair, I was responding to the claim that you actually did'nt need to use any insulation. The regs are also there to give peace of mind to a future purchaser and the confirmation that their house has been built to high standards and someone hasn't just plastered over the cracks, as it were.
Understood and apologies if my post came across in the wrong way. I agree with your and others comments later on in the thread and agree that insulation is a good thing. However, I guess that my concern stems from the fact that much of what is written relates to a 'new build' in which case it is relatively easy to implement all the various aspects of insulation.
But if you take the case of my property the rafters (made of oak) are about 80mm thick. The rooms are small. Previously there was no insulation between the lath and plaster and the sarking felt. Following the regs to the letter, my impression is that there needs to be an airgap of 50mm between any insulation and the underside of the felt? So that would leave me with 30mm of insulation before I start to encroach in the (already) small room.
If you then start talking about thermal bridging of the rafters (and does anyone know the relative thermal resistance of oak compared to softwood?) I get the impression that the BCO would like me to fix 125mm of Kingspan across the whole of the underside of the rafters.
Is that 'reasonable'?
There is a single document now that relates to work on existing buildings only (Part L1B), this refers purely to existing dwellings only not new, theres also a disclaimer in the said document that states you must do what is reasonable, if installing that thickness of insulation under your rafters would make converting the loft impractical this would be a clear argument that it is not reasonable. Have you actually read the regulations? The building regs are (believe it or not) not neccesarily cast in stone and most BC officers are a bit flexible. If you've got a real stickler thats a shame and unusual.