The Design and Construction Process Implications of the Air-tightness Requirements of the Building Regulations Part L2

Abstract

The drive to reduce the energy consumption of new buildings has been the prime motivation behind the revised Part L of the UK Building Regulations and the new Approved Document L2. Although some aspects of the requirements build on previous criteria such as increased insulation standards, new requirements including an air tightness standard for buildings present new challenges to the UK construction industry. Through presenting a case study, this paper looks at the process of achieving air tightness and learning how this new issue affects the construction process, team working, contractual relationships and the implications for the building services. Riverside House in Newcastle upon Tyne was the first building in the city to be airtightness tested to demonstrate compliance with the requirements of the new AD L2. Although the requirement for a test was introduced late in the design process, the building passed the test with an air permeability of 8.66m³/h/m² at a differential pressure of 50Pa. The design and construction team have learnt a number of important lessons from the process, namely: 1. Air tightness must be considered early in the design process and the strategy for achieving it developed at the same time if expensive remedial works is to be avoided. 2. There is never a good time to complete the test, but the earlier the better following weather tightness is achieved avoids costly removal of first and second fix items if remedial sealing works are required. 3. An air tightness champion on site with the role of implementing the airtightness strategy is recommended. 4. CIBSE design advice on infiltration allowances should be brought in line with AD L2. 5. Published advice on robust details should include building services penetrations details