Part L1B SAP Calcs for Extensions.
Building Regulations require that the glazing in a new extension does not exceed 25% of the floor area so a SAP Calc will usually be required by Building Control if you are proposing to build an extension with a large amount of glazing to demonstrate compliance with Part L1B.
Here to help you comply with Part L1B.
There are various ways to show compliance depending on the size of the extension and the amount of glazing.
For extensions slightly over the permitted amount of glazing, an area weighted U-Value calculation may be carried out on both the planned extension and a 'notional' extension with minimum u-values and 25% glazing to show the heat losses from both. If the heat loss from the proposed extension can be shown to be lower than the 'notional' then a report can be produced to show compliance with Part L1B.
For extensions with a very large amount of glazing, a whole dwelling method approach may be used. This method calculates the C02 emissions from the whole dwelling including the planned extension and compares it with the CO2 emissions from an identical dwelling with a 'notional' extension with the minimum requirements for u-values and standard openings. This gives the opportunity to offset the extra heat losses from the the overglazed extension using improvements made to the existing dwelling such as extra loft insulation, cavity wall insulation or improvements to the heating system. Provided the CO2 emissions of the existing dwelling with upgrades and the proposed extension are lower than the existing dwelling without upgrades and 'notional' extension then a report can be produced to demonstrate compliance Part L1B.