Foundational Fundamentals (Part 2): Rigid Foam, Spray Foam and Pex Tubing

The foundation work that we did today was about preventing heat loss through the floor, and providing a secure structural foundation for the ADU framing, which will begin next week.

We finished filling in the structure with gravel, and tamped it down. The gravel was leveled with a laser level. Then, the concrete was covered with a vapor barrier, which will serve to prevent moisture from rising and wicking through the concrete slab. Concrete wicks moisture upwards through a process called capillary action.

Next, the 3" of XPS rigid foam was cut out and laid evenly on top of the gravel. 1" of foam was adhered along the top of the foundation walls. This foam will help prevent heat loss from the heated slab to the uninsulated foundation walls. Any significant gaps in between the pieces of rigid foam were filled in with spray foam.

Rebar was laid out in a criss-cross fashion on top of the rigid foam to provide structural support for the concrete slab. Then, cross-linked polyethylene tubing, aka, PEX tubing was laid out and tied to the rebar with tie fasteners. The PEX tubing was laid out in two circuits that originate where the water heater will be installed.

The front porch was filled in with gravel, except around the edges. This will not be a heated portion of the concrete slab. Rebar was laid on top of the gravel for structural support. The edges of that concrete slab will be filled in with concrete, which will be more than a foot thick. This thickness will ensure that the slab is structurally supported and will help prevent settling and cracking

Lastly, the sewer line and water main from the main house were connected together and covered with soil. A sewer clean out was also installed near the foundation wall.

This video is six minutes long and covers these construction elements. Next, we're pouring the concrete slab!