Part L
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In the letter last July we set out the general position on airtightness standards and testing, as seen by Building Regulations Division. The current introduction to ADs (including AD Parl L) says that there is “no obligation to adopt any particular solution contained in an Approved Document if you prefer to meet the relevant requirements in some other way.” “Solution” here refers to means adopted by designers and builders to produce building work that is compliant with the requirements of the Building Regulations. However, as you will know, the Government often relies on ADs to give guidance on what outcome would and would not be likely to be regarded as amounting to compliance with requirements in the Regulations. In the case of Part L (a), the AD sets out, in paragraph 0.1 (c), the principle that building fabric must be “reasonably airtight” in order to meet the legal requirement in Part L (a). Paragraph 1.19 says that a way of achieving “reasonable airtightness” would be to achieve the performance standard set out in paragraph 2.4. That performance standard is in terms of a test result as obtained by applying the testing procedure in CIBSE TM 23 (footnote No 51 in ADL2).
The Part L AD does not say what designers and builders must do to achieve the performance standard set out in paragraph 2.4. Some general guidance is given in paragraph 1.19. Paragraph 2.2(b) of AD Part L accepts that, for buildings below 1,000 m2, where construction details have been proven to be robust, and the quality of installation work can be guaranteed to be satisfactory, this would be a way of showing that “reasonable airtightness” has been achieved. One aspect of the credibility of installation work guarantees is that in smaller buildings it is a practical proposition to physically inspect the joints and other risky elements of the fabric for satisfactory sealing.
It is also clear from test experts that ways can be found to test all but a small number of the very largest buildings (such as Terminal 5 perhaps), by using larger test fans, test fans in tandem and piggy-backing on the building’s own mechanical ventilation systems. Paragraph D20 in Annex D to the DTLR Circular 3/2001 indicates that where it appears at the outset that the builder will not be providing a pressure test certificate from an adequately qualified tester on completion, the building control body “should adopt an inspection regime that will allow them to satisfy themselves in other ways as to compliance [with Part L (a)]”.