A New Slab Foundation in 15 Photos
This collection of pics shows all of the main details and steps it takes to create an insulted concrete slab.
The foundation design of the 2017 FHB House project in Wilder, Vermont, was driven by several variables: thermal performance, controlling costs, and meeting the needs of target customers. You can read about how Paul and Tim Biebel balance these interests here.
This slideshow provides a glimpse of how Tim and his crew prepared the slab-on-grade foundation for the concrete subcontractor to pour the slab.
After pouring a 20-in.-wide x 10-in.-deep footing, an 8-in- thick, 4-ft.-tall frost wall is poured. Two-in.-thick EPS foam is glued to the inside of the frost wall.
The ideal time to take care of radon mitigation is before the slab is poured. This is done by running 4-in. perforated pipe 1 ft. inside the perimeter of the foundation wall. This radon collection system is connected to a vertical pipe that will run up an interior wall. Once the slab is poured, the vertical perforated pipe is replaced with solid pipe and carried to the attic. If radon mitigation is necessary, an in-line fan is added and the pipe vented through the roof. (This image is from the first home built in the development, which is why the vertical vent appears in a different location in other photographs.)
Grade beams are excavated and filled with 4-in. of foam so that there is a continuous thermal barrier.
Tim keeps a rake handy as the Amvic SilveRboard is placed to make sure the sheets lay flat and are fully supported.
Cut-outs in the Amvic to fit over plumbing risers are made with a jab saw.
Two layers of 2-in. thick SilverBoard provide R-20 insulation. The second layer is run at 90 degrees to the first layer to minimize seams lining up through both layers of insulation.
Gaps around the penetrations in the rigid foam are filled with Titebond X-Treme Mulitpurpose foam.
Rips of 2 in. by 2 in. rigid foam are cut for insulating the slab edge.
Two pieces of the 2×2 foam are placed horizontally against the frost wall to insulate the slab edge. Here Tim places the first piece. They’re held in place with dabs of Titebond construction adhesive because it sets up quickly and doesn’t expand.
As the crew rolls out the 15-mil vapor barrier the vertical slab edge insulation is visible flush with top of the frost wall.
All seams and penetrations are taped to create a continuous vapor barrier.
The sill plate helps to keep the horizontal slab edge foam in place during the pour and anchors the vapor barrier. The vapor barrier is run long around the edges. Once the walls are framed and stood up, the vapor barrier is pulled up the outside face of the wall and taped to the Zip System sheathing to create a continuous air barrier.
During the pour the concrete crew screeds off of the sill plate. The concrete is a fiber reinforced concrete.
Floating the slab.
Power troweling the slab after the pour.