What is an extension SAP?
With an Extension SAP, you can show that any heat loss through extensive glazing and openings is compensated for. This might be through high-spec insulation and the effect of solar gain.
How is it assessed?
The Extension SAP, like the standard SAP calculations, is done using drawings and specifications at the design stage.
Why is a notional vs compliant SAP required?
Building Regulations don’t allow more than 25% of a new floor area to be glazed, so if you’re going above this the Extension SAP will show that your extension is compliant by compensating in other ways. Extensive glazing can transform a living space, but you’ll want to know that the advantages won’t be outweighed by the disadvantages, for example high heating bills.
What else you might want to know…
Extensions with large amounts of glazing are becoming increasingly common, so Extension SAP calculations are now something I do frequently. I’d be happy to talk through how it all works.