Part L · residential energy

SAP Calculations Across England

Q: When should SAP calculations begin?

Begin before construction details are fixed so insulation, glazing, heating, ventilation and renewable choices can be assessed while changes are still practical.

Design and as-built energy assessment support for new dwellings, conversions and relevant residential projects, coordinated from specification through to completion evidence.

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Why start early?

Use the calculation while design choices can still be changed

SAP models the predicted energy performance of a dwelling using its geometry, fabric, heating, hot water, ventilation, lighting and renewable technologies. Starting at design stage helps the team identify where the proposed specification needs attention.

New dwellings

Assess proposed homes against the relevant Part L route and prepare the calculation information needed by the design and Building Control teams.

Conversions

Residential conversions may need energy calculations or supporting evidence depending on the approved scope. Share the Building Control request before work progresses.

Completion evidence

Update the model to match what was installed, including test results and product information, before as-built outputs are finalised.

Project stages

Connect the design model to what is built

Collect drawings

Provide scaled plans, elevations, sections, orientation and construction build-ups.

Assess the design

Model the proposed fabric, systems and technologies and identify required clarifications.

Record changes

Track product substitutions, insulation evidence, heating details and site variations.

Complete as-built

Add final specifications and relevant test evidence for the completion calculation and EPC route.

Documents and specifications

What a SAP assessor may request

Supplying clear information at the start reduces assumptions and repeated queries. Typical inputs include:

Dimensioned floor plans, elevations, sections and site orientation.
Wall, roof, floor, door and window U-values or full construction build-ups.
Thermal-bridge details and the project’s chosen calculation approach.
Heating, hot-water, controls and emitter specifications.
Ventilation strategy and product details for fans, MEV or MVHR.
Solar PV and other renewable-system sizes, orientation and product data.
Air permeability target at design stage and final test evidence at completion.

The exact assessment route depends on the building and Building Regulations application. Confirm the required outputs with Building Control and the appointed energy assessor.

Common questions

SAP calculation FAQs

What is the difference between design-stage and as-built SAP?

Design-stage SAP assesses the proposed specification before construction. As-built SAP uses the final installed specification, approved changes and completion evidence.

When should SAP calculations begin?

Begin before construction details and services are fixed. That leaves time to assess insulation, glazing, heating, ventilation and renewable choices while changes are still practical.

Is SAP the same as a domestic EPC?

SAP is the methodology used for new-dwelling energy assessment and can lead to an on-construction EPC. Existing homes normally use the current existing-dwelling methodology instead.

How does the air pressure test affect SAP?

The as-built assessment uses the applicable air permeability result or another permitted project input. Send the final test evidence before completion outputs are prepared.

Can you help if the specification changes on site?

Yes, but changes should be reported promptly with product details and evidence. Some substitutions can materially affect the calculation and may require a design response.

Related services

Coordinate your completion evidence

Need SAP support for a project?

Send the plans, site address and current project stage.

Request a SAP quote