From November 2006, Building Regulations approved document Part F1 which requires the testing of a sample of approximately 10% of all new residential and private housing.

Where ‘approved’ construction details have been adopted, one test should be carried out on each dwelling type on each development. Separate blocks of flats are treated as separate dwellings. Each of the following constitutes a change of dwelling type:

• Change in method of construction e.g. Timber frame and brick and block
• Ground floor, mid floor and top floor flats
• End of terrace and mid terrace
• Semi detached and detached
• Significant changes in building floor area i.e. 2 bed / 3 bed

Where ‘approved’ construction details have NOT been adopted, then each dwelling type is to be tested as above but with an increased sampling regime as follows:

Number of dwelling type	Number of tests to be carried out per dwelling type
3 or less	One test of each dwelling type
4 to 40	Two tests of each dwelling type
40 or more	At least 5% of the dwelling type, unless the first 5 units of the tested type achieve the design air permeability, then the frequency can be subsequently reduced to 2%.

For developments with one or two units, one unit much be tested (or two if they are dissimilar in arrangement or construction type.) The only exceptions are if:

• The identical construction has been built by the same builder within the past 12 months and successfully passed the air tightness test.
• A poor default value of 15m3/h/m2 is accepted in the SAP 2005 calculations.
  

The Building Control Officer will choose which units are to be tested – in accordance with the sampling regime defined in Part F1.