The 2018 FHB House is a net-zero energy, high-performance home in California’s Sierra Nevada foothills designed to meet the goals of the California 2020 initiative and comply with the most progressive energy code in the country. The project combines a very tight, well-insulated envelope, cutting-edge mechanical systems, and unique material choices, all wrapped up in a one-of-a-kind modern design.
Framing the First Floor Over the Pan Deck
The penalty for a durable elevated slab is a time-consuming framed floor assembly
The first floor is framed with TrusJoist TJIs in a combination of both structural and nonstructural applications. It’s this feature that has changed up the sequencing compared to our normal builds. After we framed the walls, the second story, and the roof, then we went back to frame the first floor.
The floor over the mechanical pit is the structural portion of the first floor and is framed with 16-in.-deep TJIs 24-in. o.c. The depth of these joists sets the finished floor height for the first floor.
The height of the finished floor is determined by the depth of the 16-in TJIs framing the floor over the basement. (Visible in the background.) Before framing over the slab on pan deck, the crew installed a vapor barrier of Delta-FL with all the seams and penetrations taped.
The vast majority of the first floor is the nonstructural portion and it is the bane of the whole project! The trade-off for the pan deck’s durability (a necessity because of ground water) proved to be a major pain for construction sequencing. Fitting all of the MEP (mechanical, electrical and plumbing) into a floor framed over a slab is a knee twisting, joist walking, bent-over task and it seemed to go on forever. Then we had to fit the insulation into the bays from above around all of the MEP. The Rockwool is such a nice insulation to fit as it cuts precisely and easily with a bread knife. And I think it is the best performing and environmental option today. However, after days of this we found ourselves wishing it was a blown-in product!
The non-structural floor is sort of like the roof assembly turned upside down. 4×4 sleeps are screwed in place to allow for nearly continuous insulation beneath the floor framing. One of the crew uses a laser and framing square to find the high spot along the sleeper.
14-in. deep TJIs are installed across the sleepers so they plane with the joist height over the mechanical pit foundation.
The first layer of insulation in the floor assembly is 3.5-in. thick Rockwool Comfortbatt under the TJIs.
The joist bays are then filled with layers of Rockwool after the mechanicals are run through the floor framing. In this case a return duct to the HRV.
The insulation is intentionally held slightly shy of the subfloor because the air gap will keep the floor a bit warmer under foot. All of the subfloor is glued to the joists with Advantech subfloor adhesive.
Then the AdvanTech subfloor is placed and nailed.
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Speed Square
When it comes to framing, it doesn’t get much more fundamental than a speed square — and with its sturdy metal build, Swanson’s will not let you down. Some of our team members have had theirs for 20 years.
Used to tap walls or sheathing into position, we all this the “persuader” on the job site. This is a demo model, so it can survive the job site and the back of the truck — a true must-have.
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