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SAP For Dwelling Change Of Use

Sap calculations are needed if you have altered or plan to change the use of the dwelling.


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Sap For Dwelling Conversions

Here are some types of typical dwelling change of use.

  • Several dwellings converted into a reduced quantity of dwellings
  • Converting a commercial building into flats or other residential dwellings
  • Building a barn conversion
  • Converting a house into a number of flats or visa versa

All the above illustrations will need the planned conversion to conform to Part L1B of the building regs. Part L1B mandates that minimum thermal elements need to be reached for the walls, roof, floors and glazing. The thermal values are expressed in u values. A u-value is simply a calculation of the rate that heat is lost through a specific item, the lower the value, the better the heat retention.

{A SAP EPC will required by building control for a dwelling change of use project.}

For extensions only, an EPC is normally not required. However, in certain circumstances building control may ask for an EPC and the Sap calculations, such as if the extension is over a certain size. Sap calculations may also be required for certain major renovations.

Building Regs – What’s Required

It is encouraged to have the Sap calcs done prior to commencing your building therefore you know the property will be compliant on completion. We get many requests to do Sap calculations on buildings that have already been finished. At this late stage it’s simply pot luck if the building will conform or not and any rectifications on the home may possibly be frustrating and costly.

All the calculations are done from the building plans, and so a site visit is not required. To be able to carry out the Sap calculations the following items are required:

      • Floor Plans to include sections and elevations of both the main house and the extension.
      • Construction specification of walls, roof and floors
      • Specification for all doors and windows
      • Primary and secondary heating
      • Provision for providing hot water
      • Any renewable technology (if any)

    Listed below are the targets that the thermal elements need to achieve when converting a property. New elements need to achieve the figures in Table 1 and existing elements targets are in Table 2 if they are worse that that those in the threshold column.

[table id=1 /]
[table id=2 /]

Other Services



Energy Performance Certificate (EPC)

An EPC rates the energy efficiency of a property from an A, the highest, to G the lowest. In addition to Sap calculations, an EPC will be required for all new built properties and all dwelling change of use.

Air Tightness Test

Under Part L1A of the building regulations, all newly built properties will require an air tightness test.


Water Calculations

Under Part G of the building regulations, newly built properties will need water calculations to show compliance with set targets of efficient use of water in the property.


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