This was a house, now it is 2 flats. Why does it need a SAP test?
When a house is converted into 2 flats, the use was residential before, but now the building contains 2 residential dwellings. This is a change of use, under Part L1B, and requires a SAP calculation and an EPC.
The SAP calculation needs to be done at the design stage to give plenty of time to sort out any major design problems. Part L1B requires all the walls, roof, ground floor, doors, windows and rooflights of the entire building to be up to the specified U value. The insulation in these areas needs to be checked with a U value calculation. Any dampness due to the insulation will show up in the condensation calculation and this can be allowed for in the design, for example, if a vapour barrier is needed in a timber frame wall. Another SAP calculation, the As Built, will be done when the flat is completed and the EPC will be issued then.
A refurbished building does not have to pass a CO2 Target Emission Rate like a new house does. It does not have to be especially air tight and does not need a particularly fantastic heating system. It is still good practice to try and achieve at least Band E because it is likely that in April 2018 legislation will be introduced that makes it illegal to rent a home or premises that has less than an E rating.
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