Image Credit: Eric Whetzel We installed all of the Simpson Strong-Tie brackets on the ceiling before raising any of the 2x6s. To help create the service core, two 2x6s were set on edge on top of the top plate, leaving a cavity toward the inside. Placing a strip of mineral wool insulation in this space helps keep the thermal barrier intact. Pieces of 1x4 installed between the 2x6s will prevent the Intello membrane from sagging beneath the weight of 2 feet of blown in cellulose that's going into the attic. Slits in the air barrier allowed water to drain through. Once the roof was shingled, the cuts could be repaired with tape.
Editor’s note: This post is one of a series by Eric Whetzel about the design and construction of his house in Palatine, Illinois, a suburb of Chicago. The first blog in his series was called An Introduction to a New Passive House Project; a list of Eric’s previous posts appears below. For more details, see Eric’s blog, Kimchi & Kraut.
A design goal for the ceiling was to keep mechanicals, like HVAC and electric, on the conditioned side of the ceiling air barrier. By doing this, we avoid having to insulate any ductwork for HVAC, or air sealing and insulating around ceiling lights. In effect, we completely isolate the attic, making its sole purpose (apart from ventilating our “cold roof” assembly) holding our blown-in cellulose insulation. (This setup makes it much easier to air seal the ceiling and get the insulation right — at least based on the projects I’ve read about.)
In order to do this, we created a service chase, or service core, using 2x6s set on 24-inch centers. In addition to serving as a space to safely pass mechanicals through, the only other job for the 2x6s is to hold up the ceiling drywall. The roof trusses, directly above each 2×6, are still carrying the load of the roof and stabilizing the perimeter walls.
To attach the 2x6s to the roof trusses, we used brackets made by Simpson Strong-Tie and Simpson SDS fasteners.
We installed the brackets first (see Image #2 below) before raising each 2×6 up and fitting it. Since the brackets were directly attached and under a roof truss, we were able to keep the 2x6s fairly straight, even when the board itself was less than perfect.
A feisty robin kept trying to set up a nest on our partition wall. (Our windows and doors aren’t in yet.) Apparently she believed we had created an elaborate birdhouse just for her. It took almost a week before she finally gave up — but not before starting multiple nests in multiple spots along the wall.
Maintaining the thermal layer
Along the outside walls, at the top of the wall assembly, there was a gap that we filled with strips of mineral wool insulation (see Image #3 below). This meant there will be no break in our thermal layer going from the blown-in cellulose insulation in the attic to the monolithic layer of Roxul Comfortboard 80 (2 inches plus 2 inches) that will be on the exterior side of the Zip sheathing.
Once the 2x6s were up, we had to install pieces of 1×4 between them in order to prevent the 24 inches of blown-in cellulose that will be going into the attic from causing the Intello air barrier to sag (see Image #4 below).
The plans called for the 1x4s to be installed right after the Intello but before the 2x6s, which would have been a lot easier and quicker. Unfortunately, the general contractors we fired installed the interior walls too high, making this impossible. We had no choice but to methodically cut each 1×4 to fit between each set of 2x6s. My friend OB was nice enough to help me get it done.
At first, we used “L” brackets to attach the 1x4s to the 2x6s, but this proved too time-consuming and too expensive. After experimenting with a finish nailer (too easy to miss and penetrate the Intello), we eventually settled on Deckmate screws, driving them in at an angle into the 2x6s. It was definitely a laborious process, but eventually we got into a rhythm and got it done, although we wouldn’t recommend doing it this way — way too time-consuming.
We tried to keep the 1x4s about 16 inches apart, which should prevent any significant sagging in the air barrier from occurring. (I’ll post photos once the cellulose has been put in the attic.)
In trying to avoid puncturing the Intello, I would hold a couple of fingers on the back side of the 2×6, feeling for any screws that would come through on a bad angle. A couple of times I drove a screw too quickly and paid the price.
Maintaining the Intello after installation
Unfortunately, there was a delay in getting shingles on our roof, due in large part to our first, disorganized plumber (again, more on this later). Consequently, we were in the awkward position of having our ceiling air barrier and service core all set up, but every time it rained we still had a leaking roof. In most areas, it wasn’t a big deal, but in about a dozen spots rain would collect and, if heavy enough, it would cause a bulge in the Intello. To relieve, and ultimately to avoid, this pressure, I cut small slits in the Intello where the rain would consistently collect.
I marked the slits with a red marker so I could find them later. Once the shingles were finally on, I went back and found all of these slits and taped over them with the Tescon Vana tape (see Image #5 below).
We also found a couple of weak spots in the Intello as we installed it, and even later, during the installation of the service core. These spots were marked as well, and they, too, got covered with the Tescon Vana tape just for added insurance against air leakage.
After having to fire our general contractors, we couldn’t have kept the project going without the help of family and friends. As awful as some aspects of the build have been, it’s been heartwarming to find people willing to help us see the project through to the end (much more on this later).
Get building science and energy efficiency advice, plus special offers, in your inbox.