structural elements
23
A continuous air barrier must be maintained
How many units need to be tested? All ‘non dwellings’. Dwellings are subject to a sam- pling regime. Under the 2010 revision, three tests or 50 per cent of each dwelling type must be tested. The definition of types has changed and there are likely to be more types and therefore more tests on any development. In addition to vari- ations in position (e.g. end terrace house or top floor flat), construction details and size (10 per cent difference in envelope area), other variables defin- ing type will include design air permeability, num- ber of significant penetrations (doors, windows, flues, soil vent pipes etc), storey height, and adja- cency to unheated spaces (e.g. garages, stair- wells). The process of deciding on test regimes and tracking results will become more complicated. Chiltern Dynamics has reviewed numerous
All new buildings must be tested
Part L 2010 and air tightness – more tests and tighter requirements
The 2010 revision of Approved Document L (ADL) on 1st
October will both significantly
raise the number of tests and demand much improved performance. Tom Gregory, head of Chiltern Dynamics’ Energy Services Depart- ment, answers frequently asked questions.
What do buildings need to achieve? With a 16-40 per cent improvement in the Target Emission Rate (TER) under the 2010 revisions, it is unlikely that buildings will be able to achieve the overall targets for energy improvement without significantly improving air tightness. Although ADL still states the maximum air permeability as 10m3
/(h.m2 ) at a pressure difference of 50Pa, the
actual requirement will often be significantly lower to achieve the overall TER. It is expected that typ- ically air test targets will fall from 6-10 to 3-6. In addition, for dwellings, if air test results are
to be used in SAP calculations for untested plots of the same dwelling type, a ‘confidence’ factor of 2m3
/(h.m2 ) must be added to the result. In
other words, if the target air permeability for the dwelling type in SAP is 6, the tested plot would need to achieve 4, for the result to be used for other plots.
Checking test equipment
Which projects need to be tested? New dwellings; new buildings other than dwellings; extensions to buildings other than dwellings. Overall improvements in the TER will mean that the use of an assumed air perme- ability value of 15 on smaller projects will no longer be feasible.
What are the most common air leakage/ infiltration paths? Achieving the required air permeability relies on identifying, creating and maintaining a continuous air barrier. For dwellings, this may just mean achieving a good internal finish. In more complex designs, the air barrier may be less obvious but it typically comprises external or party walls, ceilings and floors, plus elements bordering ‘unconditioned areas’ (e.g. plant rooms, garages and cold roof spaces). Extensions can create particular difficulties. It is common for air leakage paths to be ‘out of
sight’ behind dry-linings, above suspended ceil- ings, behind bath panels, kitchen units, etc. Timely inspection of these areas as well as communica- tion of the location of the ‘air barrier’ helps to reduce the risk of problems.
enq. 145
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housing developments for clients, under the new regulations. On a medium to large development, it is likely that 60-85 per cent of the units will have to be tested, rather than the 15-30 per cent typi- cally required on similar developments under Part L 2006. Furthermore, on many sites, each individ- ual plot will have to be tested if the target air permeability is so low that it makes it impractical to aim to score two points better in the test.
What sealing should take place in advance of testing? Certain temporary sealing is required (e.g. venti- lation, now including trickle vents).
Who is competent to conduct the test under Approved Document L (ADL)? Building Control is authorised to accept evidence from a BINDT-registered tester. This means an ATTMA member for non-dwellings.
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