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Implications 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
• workmanship.
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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.
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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.
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