The red line that many of us draw on the interior of our insulation to indicate the continuous airtight layer that provides comfort, optimizes the insulation and keeps it free from condensate and mold – has to be punctured at least a few times to get life necessities into the Passivhaus (water, air, electric, sewer, telecom) – so we need to seal at a minimum around the following:
- 2 ducts for HRV (supply and exhaust)
- 1 electric conduit which carries 3 cables
- 1 potable water supply pipe
- 1 sewer connection
- 1 cable/telephone wire
Although these leaks mostly do not appear on that red-line section you made, you should plan your connections to these ‘holes’ so they will be sealed properly and will remain airtight for the life of the building – which is the topic of this post – Of course, reducing the holes you have to a minimum is the first step, as it lessen the number of seals you need to make and worry about for getting to Passive House 0.6ACH50. Hence the use of service cavities to prevent unnecessary penetrations of your red line.
Recommendation number 1:
Only one pipe, cable, wire or duct per hole.
The reasoning behind this is that foam won’t expand it in the way you want it too, so it will not give you an airtight seal between the small spaces in-between the cables/pipes. This is explained quite well by Roger Lin at the bottom of this blog post of the Arlington Passive House. Furthermore shrinkage of the foam or movement of the cables will compromise foam-cable connection and thus compromise the seal. KAFLEX and ROFLEX EPDM gaskets are the preferred way to seal cables. (Note: sealing Romex will be subject of a future blog post)
Recommendation number 2: Give your self space to make a good airseal.
You need at least a few inches around a larger duct to place your hand and press the tape securely to the membrane (see photo on the right). For smaller pipes and cables, you can work with smaller tolerances, but don’t make the job harder than it should be – it is just not worth it. The picture below shows a situation in which the conduit is already installed and a gasket can be slid over it. It will be practically impossible to get a 100% seal because of the different levels of wood surrounding it.
Distribute gaskets early to plumbers/electrician so they get used
If you install gaskets over pipes and cables during installation, they remain adjustable and the connection/taping to the airtight layer can happen at a later date.Making the process quick, airtight and easy for all involved.
Yes, of course you can tape around pipes with a large amount of short strips of TESCON as shown on the right. This takes more time, is more prone to mistakes that cause small airleaks and won’t allow you to adjust the pipe anymore. However, if the pipes/cables are already installed this would be your only option, just be diligent and make the best seal you can.
Recommendation 4: No new holes!
There is a chance that you will show up on site and find some new holes in the airtight layer – new plumbing pipes, extra exterior lights, cat-doors, sewer vents, etc. Either were installed late or weren’t on the plans but that the owner really wanted them and told the contractor to install. Recommended is to explain the importance and comfort that air-tightness will bring the owners (and contractor), have them witness a blowerdoor-test early on, which will hopefully mitigate these unannounced arrival of these new holes
(during construction and during the life of the building – a dedicated service entrance could be a remedy for utility and cable companies to counter their leaking service installations – however, you still need to watch them….).