My understanding of PAS 2035 is that the presence of an openable window in a space justifies a ‘tick’ for Purge Ventilation for that space. Surveying an existing home for the Ventilation Strategy, I found a room which had a purge area 1/100th of the room’s floor area – i.e. 1/5th that required to meet Building Regs Part F. Since the room had a window which was openable, the room ‘passed’ for PAS2035 Purge Ventilation, but I felt uncomfortable with this designation. What are your thoughts on this?