Measuring subfloor ventilation rates.

This paper reports on ventilation measurements taken beneath a suspended timber floor of a BRE/DoE energy and environment test house. Sulphur hexafluoride was introduced into the subfloor void at a constant rate and the resulting concentration measured. Wind speed, wind direction, and internal, external and subfloor temperatures were also recorded. A range of air brick locations were used for each run which lasted two to three days. Analysis of the data shows that subfloor ventilation rates in this test house fluctuated widely, ranging from about 3 air changes per hour (ach) to over 13 ach. Also, the subfloor ventilation rate for this house seems to be heavily influenced by the subfloor/external temperature difference rather than the wind speed, particularly when air bricks are located on sheltered subfloor walls. The main reason for this stack dependence is that there is a significant leakage path at the wall/floor junction with air moving from the subfloor void to the gap behind the plasterboard lining.