Where buildings are concerned, the terms “Air Tightness”, “Air Leakage” and “Air Permeability” all relate to the extent to which air can move from inside to outside the building, or visa-versa, as a result of gaps, openings, porosity, etc, in the fabric. The more ‘leaky’ the building is, the more ‘air infiltration’ will occur, driven by naturally occurring forces, such as the wind and the ‘stack effect’.
Through the Building Regulations Approved Document Part L, the UK Government is driving standards of energy efficiency in buildings up, by, among other things, requiring that standards of air tightness in new buildings are both achieved and proven by means of Air Permeability Testing.
This technique establishes the rate at which air is able move through a building’s ‘envelope’ at a reference differential pressure of 50Pa (between inside and outside the building). The result is expressed in cubic metres of leakage, per square metre of building envelope per hour, at a differential pressure of 50 Pascal's, i.e. m3/(hr.m2) @ 50Pa.
The Envelope is essentially the shell of the building that contains the conditioned air, and separates it from non-conditioned areas, such as plant rooms, ventilated roof voids, under-crofts, and the outside environment.
For most building types that have to be tested under the Regulations, the maximum allowable air permeability is 10 m3/(hr.m2) @ 50Pa, although lower leakage rates may be specified as part of the overall Part L compliance strategy.
For a test to be carried out correctly, the building must have all internal doors open and all external doors (including doors into non-conditioned areas) and windows closed. Mechanical air handling systems need to shut down and sealed, and water traps needs to be filled or sealed.
Depending on the size of the envelope under test, the appropriate number of fans are taken to site and positioned and sealed into external doorways. Stroma use both electric ‘blower door’ fans and large self-powered, trailer mounted fan systems, as appropriate. Calibrated instruments are used to measure differential pressures on each floor, along with atmospheric conditions, temperatures, etc.
A series of readings for fan flow rate versus building differential pressure (nominally 15 to 65 Pa) are taken, and entered together with the building envelope measurements, static pressures, atmospheric readings, etc, into a laptop with specialist software that enables a result to be determined on site.
Depending on the result, the fans can then be used to maintain pressure and enable fault-finding using chemical smoke pencils.
For lead times and fee structures, please contact Stroma directly on 0845 621 1111 or email info@stroma.com and we will be happy to propose an approach for meeting your requirements.