Intro / Caveat
As you may know, 475 recommends you use a service cavity on the interior of high performance, airtight building envelopes. We've enumerated the values of service cavities many times, in many ways. So to be clear, our stance on the subject remains firm: service cavities are the best case scenario, and the recommended detail for any airtight assembly. With that out of the way.....
How To Stay Airtight Without A Service Cavity
It's really quite simple: every penetration through the air barrier needs to carefully considered. When you don't have a service cavity, the number of these penetrations may add up. We've covered our best practices for the major penetrations that cannot be avoided: Windows, and Existing Joists. Most everything else you'll come across is probably inset into the wall, whether that be electrical sockets, light switches, light fixtures, or vent grills. For all these elements, the air barrier will just need to go around it, dodging each switch box.
Since junction boxes and "airtight" light fixtures are not airtight, there are a few ways you could do this. One way is to wrap around each and every fixture with the INTELLO, like a Christmas present. Since we can already hear the groan that last sentence is producing, you can stop calculating the hours of labor that would take now. We have a solution for airtight boxes that have considered this problem already: the LESSCO Box from Low Energy Systems Supply Company, Inc. The installation of these boxes goes as follows:
- Attach the airtight LESSCO boxes to the stud along with the utility box (or other penetration)
- Poke a hole through the side to connect wires
- Tape off the wires as they enter the box (see this video tutorial)
- Apply INTELLO Plus to the wall
- Tape the lip of the airtight box along with any INTELLO Plus seams
This one is quick and easy: you'll need to seal every wire and pipe each time they pass through the air barrier. This probably means you're taking advantage of our bulk rates on ROFLEX and KAFLEX gaskets. [ROFLEX is for pipes, KAFLEX is for wires]
We get glowing reviews about the amount of time and energy these gaskets save in the airsealing process. You just slip them on as you install the pipe or wire. Done. Friction fit. They're EPDM rubber, so each gasket is still airtight if they move around. We suggest you hand your electrician and plumber a box or two and just have them slip them on as they work. When the air sealing team comes by, it takes just a few pieces of tape for a simple airtight seal.
In short, airtight walls can be done very well with LESSCO boxes. It just may take more labor to attend to each switch box and light fixture individually than simply strapping the wall with 2x3's. What can't be changed in a wall without a service cavity: holes in the drywall for hanging pictures or anchoring shelves will likely be a hole in the INTELLO. That's a primary reason why service cavities will always be our top recommendation.