We've had our small simple extension conditionally approved by building control, but they have said they want to see SAP calculations to show compliance with L1B as we have over 25% glazing. Extension is 8 x 3 m with two roof lanterns, two sets of bifolds and a side glazed door/wall. We live with trees around the property and want as much light as possible.
I've used the following https://www.charnwood.gov.uk/files/...e_calculator_2010/L1b_Calculator_1.3_2010.xls to get the calc numbers and I can't get the new extension to comply, however, the extension is replacing an old unheated conservatory. Should this be included in the windows and doors being replaced/removed calculation? If so this would make it compliant - the new extension will be way warmer than the current conservatory!
Reading the regs it states:
"4.2: limit the total area of windows, roof windows and doors so that it does not exceed the SUM of:
a. 25 % of the floor area:
b. the total area of any windows or doors which as a result of the extension works, no longer exist or are no longer exposed."
To me that seems to imply I could use the existing conservatory in my calculations, yes?
If not, then I think I'm looking to get a SAP engineer to also generate the calculations for me, but (as expected) they won't be compliant, what does this mean? Will the SAP engineer just say increase the rest of the house insulation etc. which will allow the extension to then be compliant?
If we choose to replace the glazed side of the extension with brick, will we have to submit a whole new Building Regs drawings and application or can we just let BCA know that that is what we will do to be compliant?
Thanks, sorry for so many questions.
I've used the following https://www.charnwood.gov.uk/files/...e_calculator_2010/L1b_Calculator_1.3_2010.xls to get the calc numbers and I can't get the new extension to comply, however, the extension is replacing an old unheated conservatory. Should this be included in the windows and doors being replaced/removed calculation? If so this would make it compliant - the new extension will be way warmer than the current conservatory!
Reading the regs it states:
"4.2: limit the total area of windows, roof windows and doors so that it does not exceed the SUM of:
a. 25 % of the floor area:
b. the total area of any windows or doors which as a result of the extension works, no longer exist or are no longer exposed."
To me that seems to imply I could use the existing conservatory in my calculations, yes?
If not, then I think I'm looking to get a SAP engineer to also generate the calculations for me, but (as expected) they won't be compliant, what does this mean? Will the SAP engineer just say increase the rest of the house insulation etc. which will allow the extension to then be compliant?
If we choose to replace the glazed side of the extension with brick, will we have to submit a whole new Building Regs drawings and application or can we just let BCA know that that is what we will do to be compliant?
Thanks, sorry for so many questions.
Last edited: