SAP & SBEM Calculations for Extensions, Conversions and Glazing
Whether you are extending an existing home, converting a building into residential or commercial use, or designing a modern glazing-heavy space, we help demonstrate compliance clearly and practically for Building Control.
Energy Compliance for Extensions and Alterations
Extensions are assessed differently from new build homes because they form part of an existing property. Instead of comparing the project against a completely new notional dwelling, the calculation considers how the proposed works affect the overall energy performance of the existing building.
This is especially important when the design includes large glazed areas, upgraded openings, new heated spaces or changes to the existing fabric and heating system.
An extension that does not meet the standard route may still be able to comply through either an area weighted U Value approach or a SAP calculation where compensating improvements to other parts of the property can be applied.
We usually start with the area-weighted U-value approach. If compliance cannot be achieved this way, we carry out a whole-house SAP calculation. The cost of the initial area-weighted U-value calculation is included in the whole-house SAP quote, so you won’t pay twice.
Pricing Guide for Extensive Glazing and Extensions
| Extensive Glazing and Extensions | Price (No VAT) |
|---|---|
| Area Weighted U Value Compliance Calculation | From £150 |
| Extension SAP Calculation | From £250+ |
| Energy Statement | From £250+ |
Not the Same as a New Build SAP Calculation
Extension SAP calculations follow a different logic from new build SAP assessments. The aim is not simply to assess a standalone new dwelling, but to understand how the extension interacts with the existing property.
This means the calculation may need to consider the existing walls, roof, floor, glazing, heating system and potential upgrades. The goal is to show that the finished property meets the required energy performance standard without unnecessary redesign.
Existing Building Impact
The calculation considers how the extension affects the energy performance of the whole property.
Fabric and Glazing Balance
Walls, roofs, floors, windows, doors and rooflights all influence the final compliance result.
Flexible Compliance Routes
Some designs can comply through compensating measures rather than reducing glazing immediately.
Building Control Ready
Reports are prepared to support Building Control review and project progression.
Clear Compliance Support for Extensions, Conversions and Glazing
- Review of drawings, specifications and existing property details.
- Assessment of proposed extension fabric and glazing levels.
- SAP calculations for extensions, conversions or glazing-heavy designs.
- SBEM support for commercial conversions or mixed-use projects.
- Area-weighted U-value calculations where suitable.
- Advice on compensating improvements if the design does not initially comply.
