How do you test?

When testing a house, we are generally sucking air from outside to the inside and passing it across the fan in a frame that has sensors around the house and outside, where we are measuring the change in pascals, or a very small unit of barametric pressure. The equipment is rather sensitive, and includes the use of a micronometer and a highly calibrated, adjustable, and powerful fan.

As you can see in the picture, we take into account the current conditions by taking readings before and after the test for things like time and date, barometric pressure, wind speed, baselines for pressure differences internally and externally, temperature, elevation, and envelope size.

The 8 to 10 readings of the test are then entered into a proprietory software package and the output is a score that tells the unintentional leakage score for your property. This takes into account the intentional leakage points like extractor vents where we have taped them up for the test. For the test to be valid, the baseline readings need to be within tolerance, which usually means that the wind speed does not exceed 13 mph. As well, the slope for the readings, gap between the readings, and any deviations need to be acceptable.

A new house in the UK is required to score at most, a maximum of 10 cubic meters squared per hour at 50 pascals. This equates to about a 10p piece (25c or quarter in the US) hole per m3 of the envelope. So, if you have a property where the envelope is 300m3, you are allowed a 'hole' in your house 1 foot by 2 foot. When you take into account all of the places that leaks can occur, this really is a low tolerance level and this is just for a marginal pass with the largest margin for error.

The overall test takes about 2 hours from start to finish. This takes into account all of the factors above and generating the report, printing the certificates, wrangling the cheque from your hands, finishing the coffee you were so kind to offer ... :)


I hope this helps :)