FHB House Framing in Pictures — Walls and Floor
Thick walls designed for continuous, full-depth insulation at the floor joists work well for production building.
The double-wall construction of the FHB House looks much like any framed wall; it’s just that there is an outer and inner wall. Connecting the two walls at the top plate and the door and window openings are the only twist. The fact that these walls are ballooned framed, though, changes the way the second floor is framed: Hanging the floor system from a ledger means continuous, full-depth insulation in the walls, but the crew has to plan ahead to maintain the integrity of the interior air barrier.
Here’s a look at how the walls and floor were framed.
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The mudsill is installed before the slab is poured and slab is screeded off the mudsill. Once the slab is poured the crew snaps lines for the bottom plate of the outer wall.
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The outer walls are framed like a standard wall: The layout is marked on the plates and the wall assembled on the slab.
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The headers are framed with Weyerhaeuser’s Parallam PSL beams. At 3 1/2 in. thick they match the thickness of the 2×4 walls so a single piece of engineered lumber is all that’s needed: quicker than nailing 2x lumber with a spacer.
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The Zip System sheathing and tape provides an integrated weather resistive barrier and air barrier.
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Zip System tape is applied at all panel ends to complete the WRB and the air barrier. For the ProHome the exterior sheathing is a secondary air barrier. The primary air barrier is on the interior.
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A telehandler helps the crew raise the exterior wall.
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Once the exterior walls are standing a 2×12 top plate is nailed on. This top plate bridges the inner and outer walls of the double wall system.
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The inner wall is framed in place. While the outer wall is framed with conventional lumber the inner walls of the kitchen are framed with Weyerhaeuser’s Timberstrand laminated strand lumber (LSL). These engineered 2x4s are dead straight for flat walls that will make hanging cabinets easier.
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The window and door rough openings are framed 1 in. larger than needed: after the sheathing is cut out of the rough openings Zip System sheathing and tape will wrap the inside of the rough opening tying the inner and outer walls together. As you can see there’s no thermal bridge at the header. This cavity will be insulated with closed cell spray foam.
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Once the walls are framed, the crew is ready to install the ledger that will support the second floor system. Before hanging the ledger a strip of Intello Plus membrane is stapled to the studs behind where the ledger is located and the vertical seams taped. Later, when the rest of the interior air barrier is installed, it will be overlapped and taped to this strip to create a continuous air barrier.
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Weyerhaeuser’s Microllam LVL will support the TJIs of the second floor.
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Their Timberstrand LSL rimboard runs parallel to the TJIs.
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To eliminate squeaks, one of the crew lays down a bead of AdvanTech subfloor adhesive before the subfloor is put in the place. It’s easy to lay down a bead of the gun-applied foam, which quickly settles down to a gel bead as seen on the TJIs in the foreground.
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The AdvanTech subflooring is impervious to moisture during the framing process thanks to the sealed edges and the fact that each wood strand in the panel is coated with a moisture-resistant resin similar to polyurethane. When they’re ready to install the finish floor there will be no swollen edges to sand down.
View Comments
Load path question: If the inner wall's bottom plate lands on the slab, how can it be the load-bearing wall? The 2nd floor joists are hung from a ledger that hangs, in turn, on the inner wall framing. That load path leads to the slab, not the footing. A sidebar explaining this engineering would be appreciated.