I was sent an email on Friday from a home owner who is reaching out to find a solution to a problem he is having whilst trying to get his extension project off the ground. With consent I am posting his emails to me in the hope that some of you very knowledgeable people with better knowledge on this subject than me can post a comment or two and help out. This was the first email:
I have designed a single storey kitchen extension. It has two number 2.1m high x 2.260m wide Beaufort bi-fold door sets in the north facing wall. I have submitted my design to local building control and they tell me “the glazing is excessive” it is more than 25% of the new floor area.
I am using an on-line LABC L1b u-value calculator [ local authority building control] to assess these u-values to get an area weighted u-value for the building, to bring it into compliance.
I don’t seem to be able to reach the desired values without having to omit one of these door sets completely!
My other option is to add more floor area…. but this means adding another 19.1 square metres to get the glass area up to 25% of the new build floor area, it only then becomes compliant on the calculator.
My question is “how are all these rather splendid nearly fully glazed extensions I see in the patio door brochures and on Grand Designs complying with the regs?” I have rigidly designed my other building elements all with maximum insulation required to meet the B. regs. ….under the floor slab, in cavity wall and in the roof space, all with Ecotherm PIR inslution. Am I missing a trick here?
My concern is that with a north facing wall the original kitchen is going to end up rather dark with only one of these door-sets installed.
After emailing him back, these were the important parts of the second email:
The actual wording in the letter from Building Control was as follows: ” the combined area of the glazing exceeds permitted 25% of the floor area, therefore please provide area weighted u-value calculations or SAP calculations to justify the excessive amount of glazing.”
I have emailed Beaufort windows web site to see if they have ‘any secrets’ but as yet await their reply.
If I added another 19m2 to the floor area of the garden room, to gain compliance with the ‘25% rule’, then with an approx. build cost of say £1000./m2 at least , this adds another £19k to the scheme.
I can see that there is possibly some reasoning in this process to reduce large areas of glass in buildings, purely as an energy saving measure, but someone please tell me how they got away with a building like the Shard !!!
This sort of subject calls for the brains and technical background that far exceeds mine!
I haven’t really come across this sort of problem before, it’s not something you hear of. Yet, when you consider this reader’s situation, it does make you wonder that if this is case, how do some of the more spectacular house designs get passed by the authorities.
If any of you clever people have any helpful feedback for this reader, please leave them in the comments section below and lets see if the glazing industry can show off it’s helpful side!