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When it comes to achieving Passive House Air tightness, its not as easy as just flicking a switch. .6 ACH @ 50Pa is an amazingly air tight building envelope, and attention to detail is critical. It cannot be under estimated.
We thought we would put together a page to help people who are seeking to achieve passive house air tightness.
Leaky staple, as you depressurize, they rip the membrane.
Passive house also requires that you have both the Outside membrane airtight to .6 as well as the inside layer however the final test to prove Passive house, is only required on the inside layer.
If you are heading toward a passive house, this article assumes you understand what vapour permeable membranes are. There are many brands of these membranes out there. If they are Passive House certified, they will all do a great job.
The 2 Big ones to look out for!
Staples – Staples can cause problems with overall air leakiness. 10’s of thousand’s of small holes add up to 1 big hole. Avoid using staples or use staples with thin pieces of packer or use double sided butyl tape on the studs and then brace the membrane into position using non structural battens, which you attach plaster board. We sell this tape, click on the link below…
In order to stop the membrane from ripping you can also use thin pieces of packers.
Bearers/Double studs and membranes – When wood penetrates through the building envelope membrane, you MUST caulk all the way in between the double stud bearers.
Pin prick of a hole
Fixing issues
- Foam a fill is not the best product to use for air tightness. If you want to use it, wait for it to dry, cut it back, and coat it with acrylic caulk.
- Use a glue for sticking the membrane down onto the floor, whether it be wood or insulated concrete. Some times its hard to ensure that the tape has stuck down sufficiently, especially when its quite dusty.
- Make sure you put pressure on the tape to dewater it
- When sticking onto wood or brick, use a butyl tape and an Acrylic Caulk (Not Polyurethane) where the bumps and odd shapes couldn’t be taken out by the tape.
- For retrofit, where there might be existing brickwork, the brick mortar needs to be sealed with a paint
- Caulk both ends of conduits, once your cables have been brought through, whether they are going inside to outside or inside to inside
- You can’t just use any type of tape, depending on the surfaces you are sticking to. Always refer to manufacturers recommendations.
Make sure the tape has been pressed down and dewatered. Use butyl tape on wood.
Expandafoam is not air tight, especially once you cut it back.
Make sure tape is consistent around windows
Too many staples. Not a good idea.
Expandafoam is not the best product to use.
Caulk inside conduits on both ends once you have brought your cables through.
Double studs leak, and they leak all the way down, caulk in between them.
Passive House Blower Door Setup
Membrane is NOT sufficiently battened off here, and could rip down.
Pressure Testing
Make sure all ceilings and walls are Battened off membrane for testing, otherwise when you depressurize the building, it could get ripped off the batons.
When trouble shooting, use the back of your hand with the building in a state of depressurization. You’ll be amazed with how effective it is. Smoke testing is over rated.
Key holes are not to be taped for the final test.
For the final test measuring the volume, of each room and it must be measured from plaster to plaster. Volume inside door ways and in the roof cavity are not included.
Battened off membrane on the ceiling