Airtight in April, Mothballed in May

Phew! With the mad rush of potting and plant deliveries out of the way for another year, and with the school where I teach having broken up for the summer, we finally have time to update the blog and start doing some work on the house once again.

In April we finished sealing round the front door and the new window, so we were able to arrange for a preliminary air-tightness test. This was to check that there were no major draughts which could be dealt with at this stage of the build, but would be difficult to sort once the house is completed. The first test involved fitting a fan into the bathroom window opening and sucking air out. This negative pressure made the green vapour barrier billow alarmingly into the rooms. In the second test, the fan was turned round and the air was blown in. The high internal pressure made the vapour barrier cling spookily to the walls.

Meter readings were taken at a range of pressures and the resulting data gave a figure of 3.3 air changes per hour. This meant little to us, but apparently it’s very good but not as good as the architects would like. However the main draught was around the flue for the gas boiler, which the heating engineers have since sealed. We are also confident that this figure will be lower once we have floor coverings in place and when the wet room floor is sealed in position. A final figure of less than 7.0 is acceptable to building control and we are certainly well within that already.