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Achieving air-tightness with building envelope refurbishment

1 November 2010 No Comment

Refurbishment of the external envelope of an existing building is often carried out as a more cost effective option than erection of a new building. Compliance with Building Regulations ADL2B can often be open to interpretation particularly considering the degree of variability between refurbishment projects.

Do I have to carry out an air-tightness test after refurbishment?

There is no requirement to carry out an air-tightness test on completion of a refurbishment. However, this does not mean that air-tightness can be ignored. ADL2B states that “reasonable provision should be made to reduce unwanted air leakage through the new envelope parts”.

Refurbishment airtightness

Uncontrolled air leakage can account for over 30% of the building envelope heat losses, so taking relatively simple and low cost steps will significantly reduce future heating energy costs and CO2 emissions.

Specifying that a post refurbishment air-tightness test is required, will ensure greater attention to detail during the refurbishment and also highlight any areas that may require some remedial action.

The way in which air-tightness is achieved will depend upon the type of refurbishment. It should also be noted that air-tightness was not a significant consideration when many of the buildings being refurbished were originally built and consequently have very poor levels of performance.

How do I achieve air-tightness during a refurbishment?

This will depend upon the type of refurbishment undertaken:

Over cladding of existing corrugated reinforced cement cladding

  • The existing cladding will not provide a suitable air-tightness layer and a membrane should be installed directly on top of this and sealed at the edges, prior to the installation of the insulated built-up cladding.
  • Failing to install the membrane will result in minimal improvement in air-tightness as the insulation cavity is vented.
  • Factory insulated composite panels can be used for over cladding.
  • Again air leakage paths need to be sealed as part of the installation.

Factors affecting air tightness

Removal of original cladding and re-sheet.

Once the original cladding has been removed, this can be treated in exactly the same manner as a new building.

The most critical stage is to identify the liner sheet as the air-tight layer and ensure that for built-up systems this has been properly sealed using suitable sealant tapes and for factory insulated composite panels that the seals have been adequately compressed. Particular attention should be paid to building details and penetrations.

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