Information for the Main Contractor

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Golden Rules to Ensure Part L is Met

Ensure that good, sound building practice is delivered so that the building is airtight. If the building is not airtight, the worst acceptable air permeability of 10m³/(h.m²) will be exceeded. The end user may also find that ventilation is inadequate and may complain of draughts at times of the year when the building is difficult to heat or cool.

State clearly in all pricing enquiries the air tightness specification and ask for details of compliance including specifications, method statements, quality audits, etc. Ensure a person on site is nominated to control and audit all aspects of air tightness works, throughout the contract period on site. Do not enclose or cover cavities or gaps before the air tightness works have been quality assured.

Frequently Asked Questions

Use similar methods to those used at present to control all aspects of contracts specification, method statements, quality management systems, etc. Problems generally occur when responsibilities for each element or package of work are not clearly defined and agreed, prior to site work starting.

If the air leakage test fails, how can air leakage paths be found?

A variety of techniques can be used to identify leakage paths. These include:

  • Feeling for draughts adjacent to the air barrier, whilst the building is being air leakage pressure tested. It is useful if the air test fan unit can pressurise and de-pressurise buildings so that draughts can be felt for on both the internal and external faces of the air barrier.
  • Running localised smoke tests using a hand held smoke generator.
  • Running a smoke test on the whole building & recording results on video.
  • Carrying out a thermographic survey.
  • Physically checking over the risk areas looking for holes, gaps, etc.

Which building components are particularly prone to air leakage?

Apart from the obvious - unsealed blockwork, hollow concrete beams or floor planks, joints/junctions in curtain walling and dry lining systems, hollow frames/ mullions/transoms, hollow steel sections penetrating the roof or walls, lap joints on roof liner sheets or T & G boarding - to name a few!

What area of leakage holes am I looking for?

Dividing Q50 by 5.5 gives an approximate figure for the total leakage area in metres squared. For example; if Q50 = 37m³/s the total leakage area = 6.7m². Treat this figure with respect and care as the visual hole seen on the air seal line is not always the actual area that air is ultimately leaking from – the final leakage hole could be a lot smaller.

When to Get Worried

Any sub contract package which proposes to use gaffer tape or plastic sheeting to air seal works.

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Air Tightness - Case Studies

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Poor Building Envelope Performance - Case Studies

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