Laing Bespoke

SAP or “Standard Assessment Procedure” is a Government approved procedure used to provide an energy rating for domestic properties.

It results in energy certification and a rating between 1 and 100. The higher the rating, the more energy efficient a dwelling. A score of 100 (or above) represents zero energy cost.

An EPC is an Energy Performance Certificate (EPC) which is given to potential buyers or renters of a particular property. The EPC report covers the energy efficiency of heating and lighting and shows the estimated CO2 emissions (Environmental Impact Rating).

For potential buyers, it shows them how much they may potentially spend on fuel costs, how much energy is wasted and whether or not the rating can be improved. Each EPC gives a property a rating from A to G; A being the most efficient rating and G the least efficient.

The test should be carried out before the property is being constructed as it may identify that the plans aren’t adequate and need to be changed to pass Regulation 26 of the Building Regulations. Once construction has started it is considerably more expensive to amend the design.

We carry out our SAP calculations before construction to give you flexibility in materials and costs and to ensure you have the best advice and information going into the project.

Yes, it is a legal requirement to have a valid EPC energy performance certificate when a home or building is constructed, sold, or rented. The EPC has to be available to potential buyers or renters as soon as you put it on the market or make any building plans.

An EPC is the industry standard in building and is defined clearly by legislation. All new build properties need an EPC in their pack for potential buyers. They are also required if a property is changing its purpose, such as a commercial property becoming domestic, as well as any residential property built from 6 April 2008.

With new build properties EPC’s can only be conducted by On Construction Domestic Energy Assessors (OCDEA’s). This is part of an accredited Government approved scheme.

An OCDEA is an authorised On Construction Domestic Energy Assessor who tests and creates a verified EPC for inclusion in Home Information Packs (HIP's) for new build, domestic properties.

Since April 2008, this has been a requirement for all new build domestic dwellings and the EPC informs new homeowners or tenants how energy efficient the property is. All new properties should take environment and energy performance into consideration when being built and upgraded.

A Predicted Energy Assessment is produced before a property has been built and is a certificate produced alongside the Design Final SAP calculation.

This is required for properties being sold off plan before the final EPC has been created for the buyers. It will then be replaced with the EPC when available. Again, the PEA can only be completed by OCDEA’s.

Before the property is completed assessors calculate the Target Carbon Dioxide Emission Rate (TER) of the property. This rate details how much CO2 it is permitted to emit, and is a minimum standard for its energy performance.

The next stage is using the actual design of the property to calculate the DER or Design Carbon Dioxide Emission Rate. In all instances, the DER should be lower than the TER so it can be approved within the predetermined environmental limits.

After construction a final calculation is made; the ‘As-Built DER’. This assessment ensures the property has an acceptable level of CO2 emissions.

U-value is a measure of the rate of thermal transmittance through a structure or material, which shows how good a thermal insulator or conductor that material is.

The U-Value is a combination of the thickness and thermal transmittance of each element within the construction of every part of a building. The lower the U-Value the lower the heat lost through the fabric of the building. U-Values are required for new buildings. They serve to give a refined and accurate figure to present to building control or add to a building energy calculation to make them more accurate.

Thermal bridging is one of the most significant sources of heat loss within a building. A conductive material or a gap in the insulation can form a ‘bridge’ between the inside of a home and the outside world, where heat can escape and be wasted.

When we talk about thermal bridging in SAP calculations, we are looking to improve construction to stop this escape of heat, and save energy. Reducing air gaps through which warm air can escape will also help with Air Permeability Testing.

Designing to address thermal bridging is now a must when constructing to pass the building regulations.

The SAP methodology caters for the fact that in many junctions thermal bridging is likely to be significant, commonly where two pieces of insulation meet, or between one surface and another. By constructing these areas with thermal bridging in mind we can lower the Psi values and improve efficiency. The most common method is by following the construction types shown in approved details schemes.

Up until now largely ignored in the UK construction industry, thermal mass (in contrast to thermal admittance) is derived from the specific heat capacity (the ability of a material to store heat relative to its mass), density and thermal conductivity (how easily heat can travel through a material). Thermal conductivity is used by SAP in the form of the ‘k’ (or kappa) value, in calculating the thermal mass parameter (TMP).

The ‘k’ value is the heat capacity per unit area of the ‘thermally active’ part of the construction element (only the first 50mm or so of thickness of the element has a real impact on thermal mass, as it reduces with increasing depth into the element; beyond 100mm the effect is negligible). It should be noted that the 'k' value is an approximation, as assumptions are made about the extent of the thermally active volumes of a material; in addition it ignores the effect of thermal conductivity in calculating the period over which heat is absorbed and emitted from the material. BS EN ISO 13786VI provides a more effective method of determining thermal mass. Thermal mass should not be confused with insulation.