What is SAP?

The Standard Assessment Procedure (SAP) has been devised as a method of measuring the overall energy efficiency of a property.

SAP has been adopted by Government as the UK methodology for calculating the energy performance of dwellings.

The SAP rating is based on the energy costs associated with space heating, water heating, ventilation and lighting.  The SAP rating is expressed on a scale of 1 to 100, the higher the number the lower the running costs.

The Environmental  Impact Rating (EIR) is based on the annual CO2 emissions associated with space heating, water heating, ventilation and lighting.  The Environmental Impact Rating is the environmental indicator that is used in the Energy Performance Certificate (EPC) it is expressed on a scale of 1 to 100 the higher the number the better the standard.

The Dwelling CO2 Emission Rate (DER) is a similar indicator to the Environmental Impact Rating, It’s purpose is in demonstrating a dwellings compliance with Building Regulations. It is equal to the annual CO2 emissions per floor area for space heating, water heating, ventilation and lighting and is  expressed in kg/m2.

The Fabric Energy Efficiency Standard (FEES) is a new compliance standard introduced in part L1A 2013 for all new dwellings. The purpose of this aspect of the SAP calculation is to ensure a good minimum standard for the basic building fabric . The Fabric Energy Efficiency Standard (FEES) is the proposed maximum space heating and cooling energy demand for a zero carbon home. This is the amount of energy which would normally be needed to maintain a comfortable internal temperature. The Fabric Energy Efficiency methodology considers the space heating and cooling demand of a dwelling and the Dwelling Fabric Energy Efficiency ( DFEE) achieved is affected by:

  • Building fabric U Values

  • Thermal bridging

  • Air permeability

  • Thermal mass

  • Features which affect lighting and solar gains

The FEE is measured in KWh/m2/yr and is not influenced by building services, for example heating systems, fixed lighting or ventilation strategy. It is a performance standard, meaning that different combinations of fabric specifications can be used to reach a particular level.

The SAP method of calculation of the energy performance of a dwelling and the associated ratings are compliant with the Energy Performance of Buildings Directive and is carried out with BRE approved software

The calculation takes into account a range of factors that contribute to energy efficiency:

  • The thermal insulation of the building fabric

  • Ventilation characteristics of the dwelling

  • The efficiency of the heating system and methods of control.

  • Solar gains.

  • The fuel used to provide space heating and water heating, ventilation and lighting

  • The impact of any renewable energy and low carbon technologies

The calculation does not take into account and is not affected by factors generated by differing life style habits or occupation patterns specific to individual households, for example:

  • Household size and make-up

  • Ownership and efficiency of particular domestic electrical appliances

  • Individual heating patterns and temperature preferences

SAP and EIR ratings are not affected by geographical location so that a given dwelling has the same rating in all parts of the UK

The procedure is applicable to self contained dwellings of total floor areas not exceeding 450m2 

When should the SAP assessment be carried out

A SAP calculation is an integral part of the design process. In order to carry out a SAP calculation  the assessor requires a full set of plans including floor layouts, elevations and sections therefore the design process clearly needs to be well progressed, however, much of the final specification required to complete the drawings to the point of being a completed set of working drawing is dependant on the outcome of the SAP calculation.   

As energy efficiency standards are constantly becoming more stringent and achieving compliance more challenging initial SAP calculations based on current basic industry standards frequently indicate a failure to achieve the ratings required to comply with the Building Regulations. Should your design fail in the initial SAP assessment I will make appropriate recommendations to alter the specification or design in order to achieve building regulations compliance.

A SAP calculation is basically a two part process, the first stage is the “Design Stage” calculation which is discussed above, the second stage is the “As Built” calculation which is carried out when the construction is complete. The purpose of the “As Built” stage calculation is to satisfy Building Control that the building has been constructed in full accordance with the Design Stage specification and also forms the basis for the production of the Energy Performance Certificate.