plications of the new regulations
Now, all new commercial and public buildings with a gross floor area of >1000 m2 must be tested for air permeability. To comply with the new regulations and pass an airtightness test, attention must be paid to:
the design detailing
construction techniques

Calculating air leakage
When the construction process is nearing completion, a pressurisation test must be carried out. The air leakage rate is then calculated using the Air Permeability formula specified by Part L2. Air permeability measures the envelope of walls, roof and ground floor area, and is defined as air leakage in m3/h per square metre (m3h-1m-2) of building envelope area at a reference pressure of 50 Pascal. The new regulations specify that air permeability should not exceed 10 m3h-1m-2.

  Key responsibilities
To avoid confusion and disputes, it is important that clients, designers and contractors understand the key responsibilities arising from the new regulations.

1. It is the client's responsibility to specify the appropriate performance requirements of the building.

2. The designer must draw up a specification for an effective and maintainable air-leakage barrier. This should explicitly refer to:
precise and workable design details for airtightness, including materials and components
the responsibilities of all parties, including
the various trades and specialists, and who pays for what
the required airtightness performance of each element and the joints between elements
the methods of checking airtightness
compliance testing procedures, including supervision.

3. Builders, contractors and subcontractors should be briefed from the outset; the designer should identify problem areas and spell out in the contract documents responsibility for finishing off.

4. The main contractor is usually responsible for arranging and paying for airtightness testing once the building is complete. There should be specific reference to testing in the pre-contract documents, in which case this requirement should be allowed for in the tender.

If there is no agreement to share responsibilities with the design team, the final responsibility for ensuring the building achieves the specified performance remains with the main contractor.