Guides
Clear explanations of compensatory heat loss calculations and the rules behind them in Scotland, England, Wales and Northern Ireland, with references to the regulations themselves.
- How to calculate the U-value of a timber frame wall, and why the studs matter
A step-by-step U-value calculation for a timber frame wall using the combined method of BS EN ISO 6946 and BR 443, with a worked example, and the common shortcut that makes walls look better than they are.
19 October 2026 · 8 min read - How much glazing can an extension have? The 25% rule explained
The 25% limit on windows, doors and rooflights in house extensions, how to work out your allowance in each UK nation, and what to do if your design has more glazing.
28 September 2026 · 5 min read - Roof windows and rooflights: which U-value to use, and the BR 443 pitch adjustment
Why a roof window's U-value changes with the pitch of the roof, when to use the BR 443 adjustment, and how each UK nation expects roof windows and rooflights to be assessed.
28 September 2026 · 5 min read - What is a compensatory heat loss calculation, and when do you need one?
When an extension needs a compensatory heat loss calculation, how the calculation works, and what each UK nation's building regulations call it and require.
28 September 2026 · 6 min read - What is an area-weighted U-value?
How an area-weighted U-value is worked out, and how it is used to show an extension complies in England, Wales and Northern Ireland.
28 September 2026 · 5 min read