Air‐tightness in the recent Part L of the Building Regulations

Abstract

PurposeThe purpose of this paper is based on recent research at Oxford Brookes University which explored how metal building envelopes can provide high levels of air‐tightness.Design/methodology/approachAn intensive research programme tested many of the foremost cladding systems used in the UK. Over 500 individual tests have produced reliable data on the performance of different joint types. This paper summarises that data and identifies key design issues and solutions.FindingsThe research has demonstrated that metal building envelopes can provide very high levels of air‐tightness providing that they are properly engineered and assembled. It also presents compelling evidence, based on whole building thermal dynamic simulations using the test data, that further increases in air‐tightness are achievable; far more energy can be saved by doing this than by increasing thermal insulation even further.Research limitations/implicationsThe testing programme concentrated on steel cladding systems, both built‐up and composite panels, with technical assessment of different joints assemblies using a dedicated purpose‐built air‐tightness test rig.Practical implicationsAs this research and other studies have shown that far more energy can be saved by achieving high levels of air‐tightness than by increasing thermal insulation even further, it suggests that a major change in regulatory strategy is now due.Originality/valueThe value of the paper lies in the originality of the testing programme and method. Although BSRIA has been testing whole completed buildings for air‐tightness using large mobile fan units pressurising the building to 50 Pa, it is the first time that a variety of cladding systems have been tested for air‐tightness on a large scale and in a laboratory environment; BRE carried out air‐tightness testing on few steel cladding systems on a smaller scale.