Wednesday, 10 August 2011


The conditions for a passive house seem fairly simple, although they are by no means easy. As far as I can tell, they amount to three things.  Insulation: the Building must lose less the 15 kWh per square metre of floor space per year. Airtightness: the building must lose less the 60% of its volume with a pressure difference of 50 pascals. Energy use: the building must use less than 120 kWh of primary energy per square metre of floor space per year. These measurements seem fairly straightforward. In Japan, insulation (Q value) is measured relative to wall area rather than floor space, and draftproofing (C value) is measured in square cm per square metre, and indicates the area of cracks in the walls. Airtightness is tested the same way in both places: by sticking a blower on a door or window, dropping the pressure and seeing how much air leaks in.

The insulators tested the airtightness yesterday, and it came to 0.3 square cm per square metre.  Apparently this is a pretty good score. In Japan 2 square cm per square metre is considered good, and less than 1 is a target for super-insulated super airtigthness. Our builder's previous best score was 0.8, and the insulators have done better still. The Passive House standard corresponds roughly to a C value of 0.2 so at first sight it looks like something is wrong.

However, we know that something is wrong. We know that there are issues with gaps around some of the windows. We know there is a gap under the door. We know that the big window doesn't close properly.  Here, the front row of the building team are doing their best to keep it shut. While the test was taking place, we went around the building sticking fingers in corners, and feeling cold air coming in in various places. 

As we know that there are problems, and the value is this close, hopefully it should reach the target when the windows are all sealed, the door has no gap under it, and the big window is fixed.