Many of the problems with achieving airtightness occur at the junctions of elements and the interfaces between different packages of work, such as the cladding and roofing systems. It is often the case that interfaces are not the sole responsibility of one subcontractor. For this and many other reasons, airtightness must be considered at the beginning of a project, in terms of design and buildability.
Typical problems include poorly filled joints in blockwork and gaps in the liner sheets of profiled cladding.
Although better airtightness leads to obvious savings in energy costs, substantial savings can also be made to the capital cost of mechanical services plant. 'If a services engineer can more accurately predict the air change rate in a building then the plant can be sized accordingly, said Stuart Borland, managing director of building envelope specialist, Building Sciences. He also points out that many clients are now interested in cutting CO2 emissions and that by addressing airtightness, such reductions can amount to tens, if not hundreds of tonnes per year. It is hardly surprising, therefore, that the drive for better airtightness is coming from insurance companies as well as services engineers and clients.
Experience suggests that although the methods of sealing buildingsare relatively simple, consideration must be paid to careful detailing, control and monitoring as early as possible. Once accidental leakage has been curtailed, appropriately managed ventilation systems can be designed and specified more efficiently for the specific building.