SAP Calculations for Extensions

If your proposed extension includes glazing that exceeds 25% of the new floor area (plus any existing windows being removed) you’ll need a SAP Calculation to demonstrate compliance with Building Regulations, specifically Approved Document L.

Please see our Other Services you might need for your project.

SAP Calculations for Extensions

What we need from you

To carry out the SAP Calculations for Extensions, we will need the following details:

  • Scaled design drawings for both the existing dwelling and the proposed extension, including floor plans, elevations, sections, and a site plan.
  • Construction specifications for the proposed extension: walls, floors, roofs, windows, doors, and insulation.
  • Details of the existing dwelling, including the approximate age and construction type of floors, external walls, and the roof (e.g. 1980s cavity wall).
  • Existing windows details, such as 20-year-old timber single glazing.
  • Current mechanical ventilation, like an extract fan in the kitchen.
  • Primary heating system, for example, a Worcester Greenstar 35CDi Compact Combi boiler.
  • Hot water storage information.
  • Any fixed secondary heating systems, such as a room-sealed log burner.
  • Details of low-energy light bulbs in use.
  • Renewable energy features, if any, like solar photovoltaic panels.

3 steps to compliance

01

SAP Assessment

We begin by calculating the Dwelling Carbon Emission Rate (DER), Dwelling Primary Energy Rate (DPER) and Dwelling Fabric Energy Efficiency Rate (DFEE) for your existing home combined with the proposed extension.

02

Notional calculation

Next, we calculate the DER, DPER and DFEE for your existing home with a hypothetical extension that meets the minimum Building Regulations standards.

03

Achieving a Pass

Your design passes if the DER, DPER and DFEE for your proposed extension are no greater than those of the ‘notional’ extension.

How it works

If the initial design doesn’t meet the standards we’ll suggest cost-effective alternatives such as improved insulation, higher performance glazing or upgrades to the existing dwelling.

Once the proposed design is compliant we’ll provide you with the SAP Calculations for Extension Report and U-value calculations for submission to Building Control.

Costs

Our all-inclusive fee starting from just £195 covers the SAP Calculations for Extensions and U-value calculations, ensuring you achieve compliance with designs that are both cost-effective and feasible.

If you have a project in mind, please send us your drawings, and we’ll provide a bespoke, no-obligation quotation.

The cost of a SAP calculation for an extension can vary depending on the size and complexity of the project.

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