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Current UK Part L Building Regulations require new buildings to achieve
an Airtightness of 10m³/m²/hour. This is comparably miles away from
the stringent airtightness parameters required to achieve Passivhaus
buildings and other sustainable structures. Our Code for Sustainable
Homes Level 6 project achieved and airtightness test result of 0.97
m³/m²/hour meaning that the building fabric was some 27 times better
than the average building in the UK.
One of the main barriers to achieving better airtightness in buildings
is that lack of knowledge in the construction industry both in terms of
airtight design philosophies and the physical construction of airtight
buildings. Often, if airtight design and construction issues are not
addressed at an early stage of the project then there is a significant
risk that the building could fail to reach a specified airtightness, or
even comply with building regs.
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In accordance with best practice philosophies and our own experience we
have developed the following simple strategy to help ensure better
airtightness:
- Set a target for the air permeability rate & ensure
that a comprehensive design review of airtightness strategy takes place
to ensure that the method for ensuring an airtight barrier is
identified; for example an airtightness membrane, such as Pro Clima
Intello could be specified. Air leakage design review workshops could
further develop detailed design, whilst including the airtight envelope
as a red line on drawings will highlight it’s importance. Finally
ensure that the air permeability requirements are written into project
specifications so that the figure required is perfectly clear to all
involved with the project.
- Ensure that airtightness
requirements are clarified when placing subcontract work orders and
that the airtightness target and methods for achieving are included in
the site induction procedures so that all trade persons are aware.
- Prior
to construction commencement appoint an ‘airtightness champion’ who
will oversee all works that will have an impact on airtightness. This
person could be the project manager, or a skilled tradesman working on
the project. They will be charged with the duty of overseeing the
quality of all works associated with airtightness, and for bringing
airtightness issues to the awareness of others working on the build.
- Implement
an airtightness quality control checking procedure to enable sign off
for different areas of the building once the airtightness envelope
works are complete; this will be controlled by the airtightness
champion.
- If possible carry out pre-completion testing
of the airtightness envelope prior to the formal air test. Speller
Metcalfe use small scale air pressure fans and ‘smoke’ pens to
facilitate this process. Weak points in the building envelope can be
identified and made good prior to the formal test, meaning that the end
result will be better.
- Carry out the formal airtightness
test using a certified air test company. On the day of the test double
check the building to ensure that all external doors and windows are
firmly closed. Additionally check that all routes for planned air
exchange such as ventilation ducts are temporarily taped over; the same
applies to waste ducts (toilets & sink drains) if the drain traps
are not filled with water. Accidentally leaving a ventilation duct
uncovered could make a massive difference to the end test result.
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