Building Regulations Part L1A for new dwellings came into force in April 2006, requiring that standards of air tightness in new dwellings are both achieved and proven by the means of Air Permeability Testing and certification.
What is Air Leakage?Air Leakage is the ‘uncontrolled’ flow of air through gaps and cracks in the fabric of the building (sometimes referred to as infiltration or draughts). Not to be confused with ventilation, which is the ‘controlled’ flow of air through purpose built ventilators. Too much air leakage leads to unnecessary heat loss and discomfort for the occupants from cold draughts.
Why should we test for Air Tightness? Gaps and cracks in the building fabric are often hard to detect simply by visual inspection. Air leakage paths through the building fabric are often obscured by internal building finishes or external cladding. The only satisfactory way to show that a building fabric is reasonably airtight is to measure the rate permeability / leakage.
Does your building need testing?All new dwellings built under the new regulations will require testing. Building Control will identify the units to be tested. The sample size depends on whether ‘Robust Details’ have been used:
- If Robust Details adopted, test one of each dwelling type on each development. If any fail, do remedial work, test again plus another dwelling of the same type on same development
- If Robust Details not adopted, the number of tests to be carried out on each dwelling type on each development are as follows:-
- 4 or less dwelling types - test one of each
- Between 5 and 40 types - test two of each
- Above 40 types - test 5% of each. For each type, this can reduce to 2% if the first 5 tests are successful.
A relaxation Applies until Oct 2007. If the first test fails, the target becomes either 75 % of difference between 1st test result & the target, or the target is increased by 15% - whichever is the higher. A higher air permeability test result can be accepted if the recalculated DER remains better than the TER (Target CO2 Emissions Rate) - in spite of the higher air permeability rate Small Developments (2 units or less).
An alternative to testing is to either prove that a satisfactory test result has been achieved on another dwelling of the same type in last 12 months, or use an assumed leakage rate of 15 m3/(m2.hr) @ 50 Pa in the overall carbon emissions calculation.
Adopting this option proves costly in achieving these results. Our input will dramatically reduce these costs. Blocks of Flats have to be considered as separate developments, regardless of how many are on the same site.
How much will it cost?The cost varies dependant on the size, number and location of the units.your tester should attempts to be as economical as possible – coordinating site visits with others in the vicinity to diminish costs to the developer.
What if it fails?Failure depends largely on build quality and initial design. Your tester should be able to offer advice – both in situ and distant – to ensure that these are suitably considered.
In the event of a failure your tester is able to carry out further procedures – such as smoke tests - to identify the problem areas. Re-tests may be done the same day following remediation measures.
How long does it take?A typical test on a 1500sq ft dwelling normally takes around 2 - 3 hours. On a larger development site, or an apartment complex, we are able to liaise with the site agents to coordinate our testing with the various trades during a typical day to ensure minimum disturbance. Others may be present on the dwelling during the test.
Can you test Air Tightness in existing homes?We are happy to test existing homes to give you an idea of where your current problem areas are – thus resulting in a more comfortable, more economic and more sustainable home.
Call Bristol DEA now to discuss on 01179 730 606.