Predicting envelope air leakage in large commercial buildings before construction.

The concept of 'build tight - ventilate right' requires minimising air infiltration through theenvelope of a building and then providing adequate ventilation in a controlled manner tosatisfy the fresh air requirements of occupants. This paper describes a simple-to-use designtool (PC based and in spreadsheet format) for predicting the airtightness of office buildingenvelopes either at the design stage or before a major refurbishment. The predicted value canbe used as an indicator for post-completion air leakage testing to confirm the designassumptions and check on build quality.Input of data is kept to a minimum. The simple design tool provides an overall leakage rate byconsidering the building size, glazed area, construction type and whether or not varioustightness measures have been incorporated. The paper concludes with good comparisonsbetween measured and predicted leakage rates in 10 office buildings. The paper also providesan example of how the tool can be used to assess the individual effectiveness of various keyairtightness measures.