February 13, 2012

Intentional "holes" in your air barrier (and sealing them)

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

Kaflex gaskets are great, but always try to minimize the number of cables first (image: http://blog.proclima.com)

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.

Only one cable per hole please

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)

Foaming many pipes and cables in one hole – looks airtight, but will still leak air (http://arlingtonpassivehouse.wordpress.com)

Recommendation number 2: Give your self space to make a good airseal.

Good amount of space to fit HRV ducts, apply insulation around them and  place ROFLEX gaskets + tape to airtight layer (http://passivhausrefurb.blogspot.com/)

 

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.

Recommendation 3:

Distribute gaskets early to plumbers/electrician so they get used

conduit to close to stud to make a proper sealed air-tight connection (vermontpassive.com)

Using TESCON in short strips to connect pipe to airtight layer

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!

This pipe and hangers were installed very late in a PH project and thus all of them needed to be taped with TESCON on each side. With some planning this could have been prevented

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….).

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One Response to Intentional "holes" in your air barrier (and sealing them)

  1. zeropassiv February 13, 2012 at 2:02 pm #

    Another issue we discovered about using foam to air seal has to do with it’s expansion property. We had just installed drywall over the weekend. The expansion foam bubbles out of the installation gap as in this picture http://arlingtonpassivehouse.files.wordpress.com/2012/01/dsc_00391.jpg

    When you install drywall against the rough opening, you need to trim that foam off. First, when you cut it open, you can really see the holes in the foam. Second, it does not come off neatly, so it is easy to take out too much foam. So, you don’t really know how much of you air-tightness layer you’ve compromised in the process.

    With this http://arlingtonpassivehouse.files.wordpress.com/2012/01/dsc_0036.jpg
    it is much cleaner and no need to trim. We actually had to re-install drywall around a couple of windows because we noticed too much foam was removed. So, I have to say, the “Quick & Foamy” may not be so quick after all.

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