Details for a Complicated Airtight Floor System

Where the parallelogram-shaped floor passes over a basement wall and onto piers, Thompson Johnson Woodworks crew provides for a continuous air barrier across the transition.

Floor-to-Wall Angle

At the out-of-square end of the house, the I-joist floor system has to join the ICF wall at a steep angle.

Angled Joist Framing

A view of the floor framing before decking is applied. At left, an LVL nailer is bolted to the ICF concrete basement wall, and the end of the ICF is attached to that member. The near end of the wood I-joist floor members rest on the mud sill.

Piers and Floor

A view of the pier-supported end of the floor system after the floor joists are installed. To the rear of the photo, under the floor, is an insulated door giving access to the basement half of the foundation.

Piers and Floor

A view of the pier-supported end of the floor system after the floor joists are installed. To the rear of the photo, under the floor, is an insulated door giving access to the basement half of the foundation.

Under-Floor Air Barrier

Where the floor system transitions across the insulated basement wall and onto the pier-and-beam support structure, the crew applied Henry Blueskin membrane to the mud sill, leaving a flap in place that will later be attached to the underside of the raised floor system. Eventually, insulators will cut holes in the underfloor air barrier membrane, dense-pack the I-joist cavities with cellulose insulation, and re-tape the holes for air sealing.

Subfloor Installation

The crew applies adhesive to the wood I-joists as they install Advantech subflooring to the assembly.

Subflooring in Place

A view of the fully decked floor system. In the lower right of the photo is the sharp angle of the corner of the parallelogram-shaped floor.

Air-Sealing the Floor-to-Wall Joint

Here is a view of the decked floor system where it abuts the ICF foundation on the uphill end of the house. Subflooring has been caulked to the framing, and the top of the basement wall has been sealed with 3M 8067 flashing tape. Two-by-four stud walls will be framed up at the edge of the decked floor, and wood I-joists will be suspended outboard of the 2x4 frame, flush with the outer face of the foundation wall insulation. The vertical I-joist wall cavities will be filled with dense-blown cellulose.

Air-Sealing the Floor-to-Wall Joint

A closer view of the floor-to-wall joints at the sharp pointy corner of the parallelogram foundation. Subflooring is sealed to framing with adhesive caulking. 3M 8067 tape forms a continuous airtight and waterproof seal across the foundation sill to the floor frame.

Air-Sealing the Floor-to-Wall Joint

Here's another close-up of the foundation and floor frame transition at the foundation corner. 3M 8067 All Weather Flashing Tape and adhesive caulking create the continuous air control layer at this juncture. Even the tops of the sill plate bolts are covered with tape.

Standing the Walls

Here's a view of the first wall in place on the completed floor deck. The framers lapped the wall sheathing down onto the floor framing, and sealed the sheathing to the foundation waterproofing membrane with acoustical sealant and 3M 8067 tape.

Wall-to-Sill Air Barrier Continuity

Here's a view of the wall-to-foundation juncture with air barrier material in place. The wall sheathing at this location laps down over the floor framing, and is sealed to the framing with acoustical sealant. The crew applied 3M 8067 tape to connect the lower edge of the wall to the tape and membrane already applied to the foundation sill, maintaining an airtight transition.

Wall-to-Foundation Air Sealing

Another view of the wall-to-foundation juncture with air barrier material in place. The ZIP System wall sheathing is connected to the foundation sill using 3M 8067 tape.

Air-Sealing the Floor-to-Wall Joint

Another view of the wall-to-foundation air control layer transition. 3M 8067 tape is used to seal the wall sheathing to the mudsill and the foundation waterproofing membrane. At left in this image you can see the flap of Henry Blueskin membrane that will be used to seal the edge of the underfloor air barrier membrane for the raised-floor portion of the floor system.

Pier Support Detail

Here's a view of the wood post and concrete pier supporting one of the corners of the raised floor. ZIP tape has been used to seal over the structural fasteners that connect the post to the wall.

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