In theory, it is the responsibility of Building Control or the Approved Inspector to randomly select which units to test. The aim is to prevent certain building units being constructed specifically for testing and therefore not necessarily reflecting the air tightness of similar units.

Approved Document L encourages the testing of units as early in the construction process as possible to allow any problem identified under test to be addressed on future units, rather than completed units of the same type having to undergo costly and disruptive remedial work.

These two factors are a little contradictory in so much that if you test the first completed unit of a dwelling type the sample will not be random (as there is only one to choose from).

There is also a practical consideration when scheduling the testing, it will be significantly cheaper and less disruptive to test 4 dwelling types on a single day rather than over 4 separate days.

It is yet to be seen quite how selection of units and timing of their testing will take place but I would suspect that common sense would dictate a balance of the above considerations.

This might affect the build programme such that an example of each dwelling type is completed early in the construction of the whole development so testing can be completed early enough to address any issues but multiple tests can be conducted.

There will need to be discussion between the contractor, testing body and controlling authority to achieve a pragmatic solution.

In practice, It is likely that the air tightness testing body will propose a test regime based on information provided by the building contractor and the building inspector will approve this.

The units to be tested are most likely to be the first completions of each type.

Back to FAQ list