How accurate is a quick SAP estimate?

This is indicative screening only — not accredited for EPC submission. Use it to flag likely pass/fail before engaging a SAP assessor.

What inputs most affect the SAP score?

Fabric U-values, heating system efficiency, ventilation type, and renewables have the largest impact. Small changes in glazing or insulation can shift the rating.

When should I commission a full SAP calculation?

Before planning compliance sign-off, EPC issue, or where funding depends on the rating. Always use an accredited assessor for the final figure.

BuildFlo Design Guide · Thermal · SAP 10 / Part L

Quick SAP estimate for UK dwellings

Indicative SAP/EPC screening before sending to a SAP assessor. Free quick SAP estimate calculator for Part L compliance checks.

What this calculator does

Quick SAP estimate helps UK building services engineers with indicative sap/epc screening for a dwelling before sending to a sap assessor. The calculation follows SAP 10 / Part L methods used in everyday MEP design — enter your project inputs below for a first-pass result.

Whether you searched for "quick sap estimate", "quick sap estimate calculator", or "how to quick sap estimate", this page gives you a working tool plus the context to use it on a real job.

When to use it

Use this for early-stage sizing and sanity checks on UK building services work. It is not a substitute for issued calculations — verify against the project specification, drawings, and relevant standard before sign-off.

How to use it

1. Fill in the inputs for your scenario (defaults are starting points only). 2. Click Calculate — results include the method and assumptions where applicable. 3. Verify against the project specification and relevant standard before issuing.

Typical output unit: SAP.

Quick SAP estimate calculator

Indicative SAP/EPC screening for a dwelling before sending to a SAP assessor

Total floor area (m²)Average storey height (m)Number of storeysBuilt formLiving area fraction

Fraction of floor area that is the living area (default 0.25)

External wall area (m²)Wall U-value (W/m²K)

Part L limiting 0.26 W/m²K (England 2021 new dwellings)

Roof area (m²)Roof U-value (W/m²K)

Part L limiting 0.16 W/m²K

Ground floor area (m²)Floor U-value (W/m²K)

Part L limiting 0.18 W/m²K

Window area (m²)Window U-value (W/m²K)

Part L limiting 1.6 W/m²K

External door area (m²)Door U-value (W/m²K)Thermal bridge y-value (W/m²K)

0.15 default details; ~0.05 with accredited construction details

Air permeability q50 (m³/h·m²)Ventilation systemMVHR efficiency (%)

Only used when ventilation is MVHR

Main heating systemHeating controlsHot water systemLow-energy lighting (%)PV array size (kWp)

Optional rooftop PV peak power

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Tips

Defaults are indicative — replace with project-specific values from the architect, structural, or MEP spec.
For issued calculations, save results in your BuildFlo project and attach to the calculation folder.
Need the regulation citation? Open BuildFlo chat in the app and ask about quick sap estimate under UK standards.

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Frequently asked questions

How accurate is a quick SAP estimate?: This is indicative screening only — not accredited for EPC submission. Use it to flag likely pass/fail before engaging a SAP assessor.
What inputs most affect the SAP score?: Fabric U-values, heating system efficiency, ventilation type, and renewables have the largest impact. Small changes in glazing or insulation can shift the rating.
When should I commission a full SAP calculation?: Before planning compliance sign-off, EPC issue, or where funding depends on the rating. Always use an accredited assessor for the final figure.