If an office is converted into flats, it is obviously a change of use. What is less obvious is that if a house is converted into flats, this is a change of use too! Yes, even though it is used for accomodation, there has been a significant change. Why is this? It is because a building subject to a change of use is subject to building regulations, and the government want to ensure that a house converted into flats wukk be insulated up to a reasonable standard.

A house or an office building which is converted into flats is classed as a change of use and subject to building regulations.

Which building regulations? Part L1B is a lower standard of insulation and carbon dioxide efficiency for an existing building, less stringent than the regulations for new buildings (Part L1A.) New buildings have to have a carbon dioxide rating which is lower than a strict target. Existing buildings don’t. Part L1B regulations require recommended levels of insulation in the walls, roof and ground floor and standards for windows, which, if single glazed, must be replaced by modern double glazing. There is a great deal of flexibility in Part L1B. The recommended levels of insulation can be reduced. It is not necessary to insulate a wall or a roof that is already insulated, even if it is insulated to a lower standard than it would be today. It is not necessary to insulate the ground floor if that would make the ceiling height too low, or to insulate the walls if adding insulation to the inside would make the bathroom so small that you would not be able to open the door, or make the stairwell so narrow that it would be dangerous. Insulation added to a building will also need to be subject to listed building conditions, if it is a listed building. If replacing single glazed windows with double glazing would be against the listed building conditions this need not be done, and, if the walls have to have lime plaster it is not necessary to install internal insulation to the walls. The listed building conditions vary according to the class of listed building. The building needs an EPC if it is possible to take reasonable steps to improve its energy efficiency. A listed building is EPC exempt only if it is impossible to make any such improvements. Sometimes insulation can be omitted from a building simply because it would be too expensive, for example, if rebuilding the flat roof above the rear of a flat which is above a shop would cost too much money. Sometimes the council won’t ask for a SAP calculation if no work was carried out on the building, for example, if an office built in the 1990s was converted into flats and the insulation and windows are good enough not to be replaced.

Minimum Efficiency Energy Standards

The other regulation that a building converted into flats will have to achieve is the Minimum Efficiency Energy Standards (MEES.) Any flats rented in the UK have to achieve a rating of band E. This means that if you want the flat to have electric heating (which is less efficient) you will have to have good insulation. If the flat has no central heating system, the SAP calculation assumes that the residents are using portable electric heaters. If the flat is not insulated to the usual standard for any of the reasons explained above, it might be necessary to fit a gas boiler and radiators in order to achieve band E. Gas gives a much better result than electric heating and hot water because the SAP calculation assumes that electricity is generated from an inefficient coal fired power station and factors this into the equation.

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When Does a Building Conversion Need a SAP Calculation and What are the Requirements?