SAP: The Government's Standard Assessment Procedure

The Standard Assessment Procedure (SAP) has been adopted by the UK Government as the methodology for calculating the energy performance of dwellings, and is now a requirement by law. This has been brought in to try to reduce the usage of fossils fuels in our everyday life.

A SAP assessment is required to be performed on the building at the Design stage, ie, before the build actually begins. The purpose of this is to ensure any improvements required to the fabric of the building to comply with legislation are identified before construction takes place.

The SAP Assessment, and the experience of the SAP asessor should be viewed as a design tool rather than an inconvenient necessity. At this stage the finer details of the design can be managed, not only to ensure compliance, but also to increase the effiency of the new home by producing better thermal performance, reduced running costs, and lowering carbon dioxide emissions. The design stage SAP will also result in a detailed analysis of the construction, heating, ventilation and insulation which in turn will form the basis for a compliance report. This can be used by Building control and Planning authorities to ascertain that the correct procedures are being adhered to, and that the eventual building will reach compliance. The resulting certification at this stage is the Predictive Energy Assessment (PEA), with its colour banded A-E European Directive efficiency guide.

SAP is the calculation method by which the carbon dioxide emissions created by the use of a building for the purpose for which it was originally intended at planning application can be ascertained. This will take into consideration the efficiency of water and space heating; the heat retaining efficiency of the building fabric elements; and the ventilation requirements of the building.

The calculation includes

• the SAP rating, amounting to the energy cost, as a value out of a hundred, which reflects the efficiency of the dwelling. The number value is also related to a visual sliding rating from A (best) to E (worst) and this is the coloured graph illustrated on the PEAs and EPCs;
• the Dwelling Emission Rate, DER, which is a measure of the actual amount of carbon dioxide in kilograms per square metre of floor area that dwelling will cause to be put into the atmosphere in the course of its day to day running in one year. This is related to the TER, the Target Emission Rate, which is the same value but calculated for a notional dwelling that meets all required specifications in all respects. For a dwelling to comply to the requirements of Part L, the DER must not be greater than the TER for that dwelling;
• the Environmental Impact Rating, EI, which is based on the annual CO2 emissions associated with space heating, water heating, ventilation and lighting, less the emissions saved by energy generation technologies. This is adjusted for floor area so that it is essentially independent of dwelling size. The EI is expressed on a scale of 1 to 100, with higher figures indicating better standards.

The procedure is applicable to self contained dwellings of total floor area not exceeding 450m2. For flats it applies to the individual flat and does not include common areas such as access corridors.  These communal areas are not calculated, unless heated, at which point they are covered by the SBEM regulations.

SAP calculations are carried out to the regulations applicable at the time of attaining planning approval, so the target achievements of each new building vary accordingly.

The SAP calculation is primarily a Design Tool in that it can establish whether the building, prior to being built, is likely to achieve the necessary compliance, and if not why not.  At this stage the Assessor can make suggestions for improvement of Design based on extensive experience and knowledge of building methods and materials. The SAP can also be completed after the building has been completed, but at this stage achieving compliance is likely to become more costly so the sooner a SAP Assessor becomes involved in the Design process, the better.  AES Southern works with the client to provide guidance and consultancy in a variety of circumstances, and will work with the client to ascertain the most cost effective way of achieving compliance.

When a SAP calculation is performed the assessor needs full information regarding the dimensions, orientation and configuration of the particular building(s) being assessed. This is best provided in the original soft copy drawing package that is widely used by the draughting industry (DWG files), but hard copy scale drawings can also be used. PDF files and photocopies are not acceptable, since the drawings must be to scale. Additionally the assessor needs the following:

• Construction details of external walls, ground floors, roof (both plane and sloping), and any other external facing elements, where known.
• A schedule of the windows, rooflights and external doors, giving sizes, construction, or, if available, hard copy evidence of the manufacturer’s determined u-value.
• The make, model and design of the space heating, water heating & storage, and the ventilation system (if one is proposed).

In performing a design SAP calculation, one of the factors under the new regulations that can greatly affect the result is the air pressure test figure. By ensuring a greater degree of air tightness, the building can be made more efficient at retaining the heat within, which may compensate for less good performance in other areas.