The regulations around air testing can appear complex.
Some dwellings need testing, yet some do not. One dwelling may also require a better result than another. So what are the rules?
The procedure and method for air testing dwellings is set by:
- Guidance set within Part L1 (latest version 2013)
- Updates to SAP conventions
- Testing standards set by ATTMA (The Air Tightness Testing and Measurement Association)
It is important to remember that unless you are building a Passivhaus, the main driver for air testing comes from SAP Calculations.
SAP Calcs measure the energy performance of the dwelling, and one key aspect of that calculation is the air tightness of the dwelling – i.e how much air is leaking out through gaps and cracks in the fabric.
Without an air permeability figure, SAP calcs cannot be completed, and without SAP calcs, air testing is pretty meaningless!
Which Dwellings Do I Need to Test?
This should in theory be decided by building control officers. In reality it is usually down to the test engineer to interpret the rules, and ensure the right units are tested. This will vary depending on the type of development. General principles are:
- 3 units of each dwelling type or 50 per cent of all instances of that dwelling type, whichever is less*
- Each block of apartments is treated as a separate development
- Tests should be carried out on first 25% constructed of that type
* If Accredited Construction Details (ACD’s) are used, only 1 unit of each type requires testing
Alternatives For Small Schemes
Small schemes are those including 2 dwellings or less. In this case there are two scenarios which may avert air testing:
1. Use a Design Air Permeability (DAP) of 15m3/hm2
This means that, as long as the dwelling still passes on the DER/TFEE criteria using this ’15’ figure, no air testing is required.
In reality is is very difficult to get a dwelling to pass in SAP with such a poor air permeabiity figure. It also has an adverse effect on the declared energy performance of that dwelling, and so is rarely used.
2. Demonstrate that during the preceding 12 month period, a dwelling of the same type constructed by the same builder was tested and achieved the DAP
If a dwelling is not tested for any of the reasons above:
- Under SAP 2005
Figure remains as per DAP (assuming test units are no worse)
- Under SAP 2009/2012
Use average of tested units plus 2m3/ hm uplift.
Therefore any untested dwellings under the later SAP regs will effectively take a ‘hit’ which will affect the energy performance of that dwelling.
For a dwelling which is a borderline pass, this may be enough to cause a SAP failure, and so the client in this case may choose to test that unit and secure a better result.
If a dwelling does not meet the required DAP, remedial works must be carried out and the dwelling re-tested until it complies. It is sometimes possible (depending on your test engineers schedule!) to retest straight away if quick, minor remedial works can be carried out. This may involve caulking or application of sealant for example.
Once the test is completed successfully, a further additional dwelling of the same type should be tested, thereby increasing the sample size.
For further reading why not take a look at: