Passive House Air Testing
Passive House Air Testing.
We have been involved with a number of developers who have been trying to build housed that score below .6 on their air test. They are not part of the Passivhaus accreditation scheme but are attempting to build ultra-low energy buildings with a target of achieving an A rating on their EPC.
Our experience so far, has been that they have struggled to achieve this for a number of reasons. One of the main ones is that they have relied on having only one air test and this has taken place far to late in the build process. Consequently it has either been impossible to identify where weak areas in the building fabric are, or identified weak areas are, either difficult to get at/expensive to rectify.
If you re planning to build a low energy or passive house, then you really need to have a minimum of two air tests. The first one should take place once the external fabric of the building is up and water tight. This should include windows and doors. The External fabric of the building is your first line of defence and you need to make sure the penetrations in the fabric of the building are kept to a minimum. The obvious ones are were services enter the building or where your extraction/heat recovery vents. The less obvious areas are where windows joint to the walls or in the case of timber frame/SIP houses, where each panel is joined or where a chimney penetrates the roof. An air test at this stage should achieve very near to the desired end result. However, if it fails to achieve a good score it is easier to identify and rectify any areas of weakness and re-test prior to proceeding with the build.
So why a second test?
Well you need a final test to produce your air test certificate which should only really be done once the house is habitable. Secondly it ensures that your build continues to achieve the desired score, after all its not all about getting the certificate, its about building an energy efficient home.
We have talked about the external skin of your build and the importance of this first line of defence. However, your internal skin is equally important and acts as the second line of defence. It is important to continue to follow the same principles as above and ensure that there are no penetrations in the internal skin. This ensures that if there is a breach in the external skin then the leak will be contained within the cavity.
What is the essential ingredient of building a low energy/passive house?
Well I think it is as basic as attention to detail.
A great example of this was a new build church hall that we tested last week in Harrogate.
The hall was built by the parishioners on a voluntary basis for no pay. Once the church had gained planning permission they utilised the existing skills of the parishioners and basically built the hall themselves. Their target air test score was below three but they wanted to achieve below 1.8 to gain an A rating on their EPC. So right from the start of the build they had energy efficiency and the air test in mind. We carried out our a free pre test site visit three weeks before the actual air test. We agreed that we would do an initial test once the windows and doors were in.
On test day we arrived to be greeted by a number of the work force who were all very interested in what was about to happen. There was a mixed atmosphere of excitement and trepidation, these people clearly cared about their building. We were shown around the build by the site manager who explained how they had prepared for the test and what they had done in an attempt to build an air tight building. He was however, still anxious about the outcome of the test.
Once we had set up our equipment I turned on the fan to begin the depressurisation process. It immediately became apparent that this was going to be a good air test score. Once we had gone through our series of pressures we were amazed to find that the final air test score was an incredible .2. We have never had such a low air test score and to be quite honest we were having some doubt as to whether our equipment was working properly. Needless to say that after carrying out the necessary checks on our equipment we confirmed that the score was correct.
So if you want to achieve Passive house standards of air tightness just do what the parishioners did and be ultra conscientious throughout your build and get everyone on board with this.
Tips from : Passive House Air Testing.
Involve us at planning stage and we can advise on both air tightness and ventilation.
Have a minimum of two air tests. The first one at watertight stage.
Maintain attention to detail and seal any penetration in the plasterboard.
Check out our top tips page and down load our air test check list.
Article Passive House Air Testing by Phil Ramshaw (Director)
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