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After spending decades doing specific U-value calculations for building regulations submissions, I am now condensing the 1000`s of calculations into a few comprehensive guides will condense these into simple screen snapshots – starting with the headline figures for Walls. These are all based on the use of foil-faced insulation such as Celotex. NB. 0.18 is better insulation than 0.28 and 0.30. NB. Mineral wool etc.. will need twice the thickness shown here…
Wall Insulation
Wall U-values Summary Sheet – SK1000
0.18 means that only a simplified SAP* calculation is needed as the solution is from a Notional Building that complies with Part L of the Building Regs. Approved Docs.
0.28 is the worst insulation for extensions permitted.
0.30 is the worst insulation for new build permitted in 2020 – I was building to this standard in 1982!
Download zip file with the sample wall U-value calculations
*SAP is short for Standard Assessment Procedure – a Heat Loss/Energy Use Calculation Method
Typical home thermal heat loss diagram
25% roof
35% wall
10% windows
15% doors
15% floor
Building Regulations – Approved Doc. L –
Homeowner Target U-values 2006-2022 – SK0000
Floor Insulation
Floor U-values Summary Sheet – SK1001
0.13 means that only a simplified SAP* calculation is needed as the solution is from a Notional Building that complies with Part L of the Building Regs. Approved Docs.
0.22 is the worst insulation for extensions permitted.
0.25 is the worst insulation for new build permitted in 2020.
Download zip file with the sample floor U-value calculations
P/A Perimeter to Area Ratios of the overall floor plate of the house affect the results I use s P/A of 0.5 as a best indicator rather than get into a debate about the inclusion or exclusion of the exiting floor plate of the existing house into the the calculation. See the graphical effect of P/A on U-Value.
Flat Roof Insulation
Flat Roof U-values Summary Sheet SK1002
0.13 means that only a simplified SAP* calculation is needed as the solution is from a Notional Building that complies with Part L of the Building Regs. Approved Docs.
0.22 is the worst insulation for extensions permitted.
0.20 is the worst insulation for new build permitted in 2020.
Download zip file with sample flat roof u-value calculations
Pitched Roof Insulation
Pitched Roof U-values Summary Sheet SK1003
0.13 means that only a simplified SAP* calculation is needed as the solution is from a Notional Building that complies with Part L of the Building Regs. Approved Docs.
0.18 is the worst insulation for extensions permitted.
0.20 is the worst insulation for new build permitted in 2020.
Download zip file with sample pitched roof U-value calculations
Loft Insulation
Loft Roof U-values Summary Sheet SK1004
0.13 means that only a simplified SAP* calculation is needed as the solution is from a Notional Building that complies with Part L of the Building Regs. Approved Docs.
0.16 is the worst insulation for extensions permitted.
0.20 is the worst insulation for new build permitted in 2020.
Download zip file with sample loft roof u-value calculations