Part L: Calculations for Extensions

In this day and age, houses are becoming more glazed and it's unsurprising that our extensions are too. unfortunately, Section 10.7d of Part L 2021 reminds us that the combined area of windows, rooflights, and doors in an extension must not exceed 25% of its floor area plus any openings lost to the new build.

However, we can perform a SAP calculation to ensure compliance no matter how much glazing you wish to add.

compliance is shown by comparing the emissions of two calculations; an As Designed and a Notional; where the notional dwelling is the same as the As Designed but meets minimum standards. If the As Designed emissions are equal or lower than the notional, the dwelling is compliant.