Homeowners and architects increasingly choose large windows, sliding doors, and rooflights to bring natural light into their homes, but a highly glazed extension can often trigger the need for a SAP calculations under Part L of the Building Regulations.

If your extension has more than 25% glazing, you’ll almost certainly need a SAP assessment. At MES Building Solutions, our SAP assessors help you meet regulations without reducing your glazing, using a detailed, whole-house approach that goes far beyond a basic heat loss calculation.

A SAP calculation assesses the energy performance of your home when a new extension is added. SAP looks at how the entire property performs, including:

This gives you a far more accurate picture of how your extension will impact energy performance and more ways to achieve compliance.

One of the biggest advantages of SAP modelling is that it allows you to keep your design intact. Instead of altering elevations or reducing glazing, we can offset additional heat loss through targeted improvements.

Examples of improvements that can help your design pass if necessary:

Because SAP looks at overall performance, even small upgrades can make a big difference.

If your extension faces south, south-east, or south-west, large glazed areas can significantly improve solar gain. This helps reduce heating demand at certain times of the year.

SAP calculations factor in this positive impact, which can offset the additional glazing and help your project meet Part L more easily than expected.

This is a major advantage that is completely missed by the simpler area-weighted U-Value approach.

At MES Building Solutions, we specialise in SAP calculations for domestic extensions, helping clients achieve compliance while keeping their vision intact.

Whether you’re an architect, builder, or homeowner planning a highly glazed extension, we’ll help you meet Part L requirements while maximising your design.

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