The California FHB House Air-Sealing and Insulation in Pictures
Delta air barriers and tapes and Rockwool insulation on the interior and exterior of the building envelope are key components of this high-performance house.
The California house is planned as a net-zero house—actually it’s modeled to generate more energy than they’ll consume. While homeowners Mela and Dave are not seeking Passive House certification on this project, they are targeting Passive House performance levels. To achieve this level of performance they need a well-detailed air barrier strategy and enough insulation to reduce heating and cooling loads dramatically relative to a code-built house.
Click on the slideshow link below to see how they air-sealed and insulated the house.
More about the California FHB House:
The walls of the basement mechanical room are highly-insulated with R-31 of Rockwool. There are two layers of 2-in.-thick rigid panel ComfortBoard 80 applied to the interior of the concrete walls. After the slab is poured a 2×6 wall is framed and insulated with ComfortBatt.
There are 5-in. of ComfortBoard 110 beneath the Delta MS dimple mat. For air-sealing, all penetrations through the Delta MS subslab vapor barrier are taped. The vapor-variable Delta Sd-Flexx on the walls is also taped to the perimeter of the Delta MS. The Sd-Flexx is carried past the overhead floor framing to the pan deck and connects to the air barrier at that level.
A tight house requires a continuous air barrier. The air barrier for this house is at the sheathing. Delta-Vent SA is applied to all of the walls as the weather-resistive barrier (WRB) and air-barrier. The self-adhesive barrier is vapor open so the wall assembly can dry in both directions.
At the top of the house the air barrier continues at the sheathing surface. Here, all of the plywood seams are taped with Delta Multiband to create the air barrier. The roof/wall intersections along the rakes and eaves are sealed with 9-in. Delta-Flashing to connect the wall air barrier to the roof air barrier.
Once the roof is air-sealed Delta Vent-S is rolled out as an underlayment.
A 5-in.-thick layer of Rockwool on the exterior of the roof helps keep the sheathing warm to prevent condensation on the sheathing. The TopRock DD is an extremely dense mineral wool board designed for low-slope roofs. The metal roof can directly overlay the insulation without an additional layer of plywood over the insulation. Insulation netting is stapled to the underside of the TJI rafters and the bays are dense packed with blown-in fiberglass against the bottom of the sheathing. The roof assembly is R-83.
Continuous insulation on the exterior drastically slows thermal bridging. The two layers of ComfortBoard 110 are staggered so that seams don’t line up. The insulation is dense enough that it won’t compress when the siding is installed over the insulation.
Rockwool can be cut with their serrated handsaw or a kitchen knife or electric carving knife–the last two options were most frequently used by the crew.
The elevated pan-deck that forms much of the first floor has a several layers of insulation.
Delta-FL dimple mat is the vapor barrier for the slab. All seams and penetrations are taped and integrated with the taped wall plate/curb connection. The first layer of insulation is 3.5 inches of ComfortBatt that runs under the TJI floor joists to limit thermal bridging.
Once the joists are in place additional layers of ComfortBatt fill the 14-in. deep joist bays. Because the floor deck is 17-in. above the slab (and wall plate in this curbless south wall) the lower portion of the wall is insulated at the same time.
The last layer of insulation brings the floor assembly to R-68. The top of the batts is flush with the bottom edge of the TJI flange. Not only does this save the crew from rabbeting the batts to fit around the flange, but the 1-in. air gap beneath the floor sheathing keeps the floor slightly warmer and more comfortable.
After all of the wall have been insulated with R-23 batts of Rockwool, the gaps between the windows and the rough openings are stuffed with Rockwool scraps and then taped on the interior as part of the air sealing strategy.
When the blower door was set up and the test run, they successfully met their target of 0.6 ACH50.
Looking at the exterior of the house with the Flir C3 thermal camera shows very even temperature across the exterior of the house.