Question 1

What is a SAP rating?

Accepted Answer

A SAP rating (Standard Assessment Procedure rating) is a numerical score on a scale of 1 to 100+ that represents the energy efficiency of a dwelling. The calculation is based on the energy required to heat and provide hot water to the dwelling over a standard year, divided by the floor area. Higher scores indicate more energy efficient dwellings. A score of 100 means zero energy cost; scores above 100 indicate energy-generating dwellings (with PV or other renewables). The SAP score is converted to the A-G EPC band (A: 92+, B: 81-91, C: 69-80, D: 55-68, E: 39-54, F: 21-38, G: 1-20). New dwellings must achieve a minimum EPC B rating under Approved Document L 2021.

Question 2

What factors affect the SAP score?

Accepted Answer

The main factors affecting the SAP score are: fabric U-values (walls, roof, floor, windows and doors - lower U-values improve the score); air permeability (tighter buildings lose less heat through infiltration); heating system efficiency (heat pump COP, boiler efficiency); hot water system efficiency; lighting efficiency; ventilation strategy (MVHR with high heat recovery efficiency and low SFP improves the score); renewable energy (PV panels reduce the net energy demand); and thermal bridging (the y-value or psi-values of junctions in the fabric). The SAP calculation also accounts for orientation (south-facing glazing captures more solar gain), floor area, and the ratio of exposed surface area to floor area (a compact building performs better than a sprawling one).

Question 3

When is a SAP calculation required?

Accepted Answer

A SAP calculation is required for all new dwellings (houses and flats) under Approved Document L. It must be carried out twice: a design-stage SAP (using design data) before construction begins, to demonstrate that the proposed design will meet the required performance; and an as-built SAP (using actual data from the pressure test, commissioning certificates, and any design changes during construction) after completion, to confirm actual performance. The as-built SAP data is submitted to Building Control and used to generate the final EPC. SAP is also used for conversions and material changes of use where an EPC is required. Extensions and renovations typically use a simpler assessment (a notional building calculation) rather than whole-dwelling SAP.

Question 4

What is the difference between SAP and SBEM?

Accepted Answer

SAP (Standard Assessment Procedure) is used to assess the energy performance of domestic dwellings (houses and flats). SBEM (Simplified Building Energy Model) is used for non-domestic buildings (commercial, industrial, public). Both are government-approved methodologies for demonstrating compliance with Part L of the Building Regulations, but they use different calculation methods appropriate to their building types. SAP is simpler and focuses on annual space and water heating energy cost per unit area; SBEM is more complex and assesses a wider range of building energy uses. Both generate an EPC - domestic EPCs use A-G bands from the SAP score; non-domestic EPCs use A+-G bands from the SBEM asset rating.

SAP Rating

Just so you know...