SAP Calculations 

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SAP (Standard Assessment Procedure) calculations are required under Building Regulations Part L for all new dwellings, and in some cases for conversions and certain extensions.

They measure the energy performance of a home and are used to create your Energy Performance Certificate (EPC).

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A SAP assessment must be submitted before construction begins, and an EPC is required once the home is completed.

 

What SAP Measures

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SAP assesses the energy efficiency of a home based on:

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• Building fabric (walls, floors, roofs, insulation)

• Heating & hot water systems

• Ventilation

• Internal & external lighting

• Renewable technologies (solar PV, heat pumps, etc.)

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SAP gives a score from 1–100+:

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• 100 = zero energy cost

• Above 100 = produces more energy than it uses

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The 3 Stages of a SAP Assessment

1. As Designed Stage (Pre-Construction)

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Your designer submits plans, sections, elevations and a specification to a SAP assessor.

The assessor then calculates:

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• Floor areas & heat-loss areas

• U-values of all building elements

• Heating, hot water & ventilation performance

• Window/door performance

• Renewable systems

• Thermal bridges

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If the design fails Part L requirements, the assessor suggests improvements (better insulation, lower-U-value windows, more efficient heating, or renewables).

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Once compliant, the assessor produces:

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• SAP Reports

• Predicted Energy Assessment (PEA) – required if the home is marketed for sale

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These are submitted to Building Control.

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2. Build Stage (During Construction)

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Any changes on site must be checked with the SAP assessor, as even small alterations can cause a fail.

Key points:

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• Air pressure testing is required.

• “As-built” details must match the design submitted.

• If changes reduce performance, additional upgrades may be required.

• Most issues occur when builders diverge from the specification without consulting the assessor.

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3. As Built Stage (Completion)

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Once the home is finished:

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• The assessor adjusts the SAP for the actual air test results and any approved changes.

• Final SAP calculations are completed.

• The Energy Performance Certificate (EPC) is issued.

• Supporting documents (SAP worksheet, data input reports) are sent to Building Control.

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An EPC is required before the home can be sold or rented.

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Information Needed for SAP Calculations

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Minimum documents required:

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Drawings

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• Site plan with orientation

• Plans, elevations & sections (scaled or fully dimensioned)

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Construction Details

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• Walls, floors & roofs with insulation types/thicknesses

• Windows/doors (sizes, U-values, glazing type, manufacturer certification if needed)

• Thermal bridge details (approved or bespoke)

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Heating & Ventilation

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• Boiler/heat pump model

• Heating controls

• Hot water cylinder details

• Mechanical ventilation specs

• Secondary heating (wood stove, etc.)

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Lighting

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• Low-energy lighting design details

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Renewables (if used)

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• PV panels

• Solar thermal

• Waste water heat recovery

• Heat pumps

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U-value calculations from manufacturers are acceptable where applicable.

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Why It’s Important to Get SAP Done Early

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• Prevents costly redesigns

• Avoids delays at Building Control

• Ensures the home passes Part L

• Helps you design an energy-efficient and future-proof home