The air leakage target has been set to a figure of 3m2/m2/hr which is equivalent to 0.4 air changes per hour when the PHPP spreadsheet is used, according to engineer Chris Croly of BDP [editor’s note: there can be much greater variation between n50 and q50 figures in non-domestic buildings compared to domestic, due to their geometry and size]. The development is expected to employ a mixture of natural and mechanical ventilation.