Part L1: SAP Calculations and Energy Performance Certificates

The standard assessment procedure (SAP) as developed by BRE is the adopted methodology for calculating the energy performance of newly constructed and converted dwellings.


New Dwellings

It is required that all new dwellings have a SAP calculation carried out to:

  • demonstrate compliance with Approved Document L1A of the Building Regulations
  • generate an Energy Performance Certificate (EPC)

Typically, SAP calculations are undertaken at “Design” stage to ensure that the proposed building complies with current building regulations and achieves any related planning conditions. This specification should then be incorporated throughout construction.

These calculations are then updated upon completion of the building to reflect the “As Built” performance of the building.

Waterstone’s team of energy assessors have many years experience in carrying out these assessment for developments ranging from a single house to large multi-residential mixed use schemes in excess of 300 dwellings.


Conversion (change of use)

Where buildings undergo a material change of use, for example conversion of a commercial building to residential. It is necessary to carry out a SAP calculation for the dwellings to:

  • demonstrate compliance with Approved Document L1B of the Building Regulations
  • generate an Energy Performance Certificate (EPC)

Waterstone’s team of energy assessors are experienced and well versed of the Building Regulations and construction methods in order to advise the measures necessary in order to ensure the best results within the calculations.



Where an extension may include a significant area of glazing (greater than 25% of the extension floor area), it is likely that building control will request a SAP calculation to demonstrate that the energy efficiency does not suffer as a result.

Our team of energy assessors can assist with demonstrating compliance and advise of any measures which may need to be incorporated to satisfy building regulations.

Accompanying Services

  • Code for Sustainable Homes
  • U Value Calculations
  • Thermal Comfort Analysis (Overheating) Calculations
  • Linear Thermal Bridging Calculations
  • Water Calculations (Part G)
  • Mechanical and Electrical Services