Blue Tree Acoustics Frequently Asked Questions (FAQ) #12


How does Air Tightness relate to carbon emission rates calculated using SAP or SBEM?


Air tightness or permeability is an important factor in calculating the overall carbon emission of a building.

The Standard Assessment Procedure (SAP) method is used to assess dwellings under 450m2 floor area.

The Simplified Building Energy Model (SBEM) method is used for buildings other than dwellings.

Whichever method is used, a Target Emission Rate (TER) is calculated prior to the start of construction. The Target Emission Rate is the amount of carbon that a well designed building of this size of the actual building should produce.

Then the SAP assessor calculates the Dwelling Emission Rate (DER) or Building Emission Rate (BER). The DER or BER is based many factors unique to the building such as orientation, glazing type and amount, insulation type, heating system type and fuel type, sizes of walls, ceilings, floors, number of radiators etc.

The DER cannot be greater than the TER and to achieve this some of the proposed design elements might have to be changed. Materials might be changed for materials with better U-values, maybe the amount of windows is reduced, maybe the heating system is changed.

To calculate the DER the above details are entered into the SAP software along with a Design Air Permeability. The Design Air Permeability is what the SAP assessor thinks that the building will achieve when tested. This value must be less than or equal to 10m3/(h.m2) @ 50 Pa or 15m3/(h.m2) @ 50Pa.

The building is then constructed and the air tightness performance is tested. The actual tested air permeability figure is entered into the SAP software and this generates a final (DER).

The actual DER or BER must be lower or equal to TER.

This means that the tested air permeability must be no more than the design air permeability figure.

Blue Tree Acoustic Provide both (Air Tightness Testing) and (SAP/EPC) calculations.

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