What is a SAP calculation?
A SAP calculation is a spreadsheet-based calculation that is used to determine a building’s heat gains and losses. SAP refers to the “Standard Assessment Procedure”. It assures Building Regulation compliance at the design stage and provides an energy rating.
Basic SAP calculations are always required for any extensions to existing structures that will contain more than 25% of the floor area as glazing. New builds will always require a more thorough SAP and energy certificate. This simple SAP calculation is required to determine if an extension will lose or gain too much heat throughout the winter and summer seasons, respectively, as wall structures are always thermally superior to glass, even when using triple-glazed, coated glass.
The “elemental method,” is used to demonstrate the thermal performance of existing buildings, which is required in Part L of building regulations. In this method each component of a building, such as the windows, doors, walls and floor, must meet a minimum thermal performance to be deemed compliant. These are laid out in accordance with “typical” percent areas of a “nominal” extension plan. Therefore, if there is more glass than is anticipated, as is often seen in modern construction, the building will be more prone to heat loss and overheating, thus compliance must be demonstrated with a SAP calculation.
The size and orientation of windows and rooms are considered in the calculation and a choice of several heating system options is offered. The calculation results in a value that represents a pass or fail in comparison to the “notional” house which has minimal glazing and requires on additional proofs in order to pass building regulation.
To reduce the amount of heat lost or gained from glazing there are several improvements and modifications that can be made. Making these changes means that the extension design does not need significantly altered. Some changes include upgrading the boiler, adding insulation elsewhere or improving thermal efficiency in other areas of the building.
Only individuals or businesses with the licensed software are able to complete SAP Calculations remotely. Many architects instead employ an external consultant, whose involvement depends on the intricacy of the design (for example, new builds are more complex). Straightforward or slightly non-compliant designs require only a quick straightforward service, with costs averaging in the region of £150-£300. More complex design projects that require numerous tires to get the design to pass the SAP calculation will involve higher costs.
In some cases, building control are happy to proceed without a SAP calculation, even if an extension exceeds the 25% rule of thumb, provided substantial other improvements are taking place, but this is dependent upon each project and Building Control discretion. TSA can arrange for a SAP calculation to be carried out should building control request, or the glazing is significant.
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