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Golden Rules to Ensure Part L Is Met - Ensure air tightness is thought about at the concept stage of the project and designed in from the start.
Ensure that all materials and components used for air tightness purposes have a similar specification and longevity as all others used on the project. There is no reason that buildings constructed to an airtight standard should be stuffy for occupiers or be at greater risk from condensation. The rule is: build tight – ventilate right.
Ensure that all areas of the air barrier (air seal line) are sealed right, first time. Air leakage from the building fabric should be low but need not lead to a stuffy internal environment. The ventilation of rooms should be designed to ensure the number of air changes per hour and amount of fresh air is adequate to maintain indoor air quality.
FREQUENTLY ASKED QUESTIONS:
Is there a risk from making a building envelope too airtight?
Part L is meant to control the amount of uncontrolled air leakage through the building fabric, not the amount of controlled ventilation. However, naturally ventilated buildings should not normally be conducted to <2m³/(h.m²).
Is the target air permeability rate achievable?
The worst acceptable air permeability rate of 10m³/(h.m²) set down in Part L is achievable when current best practice for buildings is around 2m³/(h.m²). However, if no regard is taken to air tightness, it is probable that Part L will not be complied with.
How expensive will it be?
Additional building costs may amount to 0.5%. This ignores cost savings from downsizing heating plant and the lifetime reduction in energy costs.
Why do some consultants state air permeability and some air leakage index and what is the difference?
Air permeability –determined in the new Part L Regulations. The envelope area of the building includes the total area of the roof, walls and ground floor.
Air leakage index – used by most consultants in the UK up to 2001. The envelope area included for the area of the roof and walls only. The ground floor was not included as most floors in the UK are concrete slabs – i.e. impermeable to air. Air leakage index figures are therefore more difficult to reach than a similar air permeability figure!
50 Pascals – the nominal pressure that air leakage is quoted at. Note, during a thunderstorm typical localised air pressures can rise by 500 Pascals. There is no risk of the air leakage pressure test damaging the fabric of the building. 50 Pascals is similar to the pressure felt from blowing lightly onto the back of your hand.
When To Get Worried
When a party claims that air leakage problems will be sorted out after the first air leakage test and will not be remedied until then. HRS’s golden rule is that it costs considerably more to put right second time, rather than doing it right first time. Ensure that maintenance procedures take air tightness into account. Degradation or damage to air tight elements or components needs to be minimised over the long term. We have witnessed how simple it is for an electrician to punch a large hole through a wall, thereby increasing the air permeability figure significantly enough for users of the building to complain about an increase in draughts.
Clients HRS SERVICES have worked for
Sound, professional working relationships have been built up with many blue-chip clients and large construction organisations. Our skills and expertise have been gained from successfully air sealing over 250 buildings across the UK and Europe, for blue-chip clients such as BAE Systems, Consignia, Norwich Union and Tesco. Repeat business has been gained from contractors such as Bovis Lend Lease, HBG, Simons, Bowmer & Kirkland, Mowlem, Kier, Britannia and Dudley’s. HRS is certified to ISO 9001 and UKAS for all air tightness operations. HRS are full members of the ATTMA, which is recognised by Building Control and Approved Inspectors as competent persons”, as required under Part L. HRS hold P.I. insurance with cover of £2M for testing and consultancy works.
Air Tightness - Case Studies
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Article from Building Magazine published 12.08.2011
Tightest building in UK Air test result <0.5 m³/hour/m², HRS involved throughout
IKEA employed the UK's largest fan to check the air tightness of its Glasgow store
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