Part L of the Building Regulations requires a level of air permeability in new
buildings, as part of the measures needed to reduce heat losses. This requires
testing to establish the volume of air escaping through gaps, cracks and holes,
to ensure that the standard of less than 10 m 3 of air per hour for every square
metre of the envelope is not being exceeded. This paper describes the most
signifi cant air paths and some of the design and detailing measures that can
reduce air losses. Services are cited as a major source of air leakage, and
the paper identifi es the responsibility of services engineers in maintaining
a continuous barrier to air leakage. A dual process of education of services
tradesmen and timely inspection is proposed to ensure that air tightness levels
are not compromised. The period just prior to handover of the property is seen
as the optimum moment for undertaking air tightness tests.

• Timely inspection a must