5 Steps For Sealing Intentional Holes in Your Air Barrier
A continuous air barrier is one of the defining design details of Passive House and high-performance building. The red line that many of us draw on blueprints to indicate the air barrier separating the interior conditioned space and the exterior environment, provides comfort, optimizes the insulation, and helps keep the assembly free from condensation and mold.
While typical constructions have a multitude of compromising penetrations, the air barrier in a high-performance construction should continue uninterrupted. But in order to get necessities such as water, ventilation air, sewer, , telecommunication - and people for that matter - into and out of the space, some punctures are unavoidable.
So we’re going to have some holes. The holes need to be intentional, integrated, and durably sealed for the life of the enclosure and building. Here are five simple steps to sealing these intentional holes in your air barrier:
STEP 1: Do you really need that hole?Minimize the number of penetrations.
The first step is reducing the number of holes. By minimizing the number of seals you need to make, you minimize the number of seals you need to worry about to get to Passive House 0.6 ACH50. The best way to minimize these holes is by using a service cavity. With a service cavity in place, the multitude of power outlets and switches aren’t also a multitude of holes needing sealing.
What we’re left with then, in a typical house, might be:
- 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
- Windows and doors
This is a manageable number of penetrations - allowing for appropriate quality control of execution and the desired airtightness result.
STEP 2: Elbow roomGive yourself space to make a good air seal.
Treat air barrier penetrations like you would roof penetrations that need rigorous waterproofing - place them with enough space to work around them. Don’t jamb wire or pipe penetrations into framing corners. Give them space. You need to be able to not only work around these penetrations, but possibly repair them after testing.
Good amount of space to fit HRV ducts, apply insulation around them and place ROFLEX gaskets + tape to airtight layer (http://passivhausrefurb.blogspot.com/)
In order to properly seal a larger duct or pipe, you need space to get our hand around it and press the tape securely to the membrane. For smaller pipes and cables, you can work with smaller tolerances, but don't make the job harder than it should be. The picture below shows an already-installed conduit with barely enough space for a gasket to be slid over it. It will be practically impossible to get a 100% seal because of the different levels of wood surrounding it.
Set yourself and the on-site team up for success by leaving enough space around these penetrations for proper sealing.
STEP 3: Seal of approvalUse the right materials to get an airtight seal.
First, don’t use spray foam - particularly not “Great Stuff” and the like. Walking through the project a blitzing every pipe and bundle of wires with a squirt of spray foam may sound really easy, but it’s a long-term recipe for disaster. Foam won't expand the way you want it too, so it will not give you an airtight seal in the small spaces between cables/pipes. This is explained by Roger Lin in his blog post on the Arlington Passive House. Shrinkage of the foam or movement of the cables will compromise foam-cable connection and thus compromise the seal. Foaming many pipes and cables looks airtight, but will still leak. Foam fails.
Use products designed to do the job at hand:
- Cable connections: KAFLEX, KAFLEX MULTI and KAFLEX POST. If these gaskets aren’t available, you can use TESCON VANA or PROFIL tapes and bookend them as a back up.
- Pipe/Duct connections: ROFLEX and ROFLEX SOLIDO gaskets. ROFLEX has a flexible rubber sleeve that fits around the pipe/wire and can easily accommodate any movement while maintaining an airtight seal. ROFLEX SOLIDO gaskets have built-in tape that seals directly to your air barrier (whether it’s a Pro Clima membrane, plywood, drywall, masonry, etc) without the need for primer. Again, if the gasket is missing from the tool box, short strips of TESCON VANA or PROFIL feathered around the component can get the job done.
- Windows and Doors: these deserve a blog post all their own. Read it here.
STEP 4: All together nowDistribute gaskets early to plumbers/ electricians so they get used to using them.
Building a Passive House is an exercise in cooperation and communication between trades. If gaskets are installed over pipes and cables by plumbers and electricians during installation, they remain adjustable, and the connection to the airtight layer can happen at a later date. This workflow makes the process quick, airtight, durable, and easy for everyone involved.
Yes, of course, you can tape around pipes with dozens of short strips of TESCON VANA, but this takes more time, leaves you more vulnerable to small air leaks, and won't allow you to adjust the pipe anymore. If the pipes/cables are already installed, this is your only option, just be diligent and make the best seal you can.
STEP 5: 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. - that were either installed late or weren't on the plans (but that the owner really wanted and told the contractor to install). The unannounced arrival of these new holes can be mitigated through communication. Explain to both the homeowner and the contractor the importance of airtightness and the comfort it provides early on in the process. Have them witness a blower door-test so they understand the goal that you're working towards. Make them your partners in airtightness.
Like so many things in life, a little advance planning and communication will save you a lot of trouble down the road. After seeing many projects hit 0.6 ACH50, whether after 1 or 10 blower door tests, these are the five steps that we know will make air sealing less of a headache. We hope these recommendations will help your next Passive House project run a little smoother.