With the gravel subfloor leveled and all of the plumbing and ductwork installed, it was time to prep the floor for radiant heat. The idea is fairly simple, you embed closed loops of tubing (called pex) in the concrete slab, heat water, and circulate it through the floor to bring it up to the temperature you want.
We spent quite a bit of time getting the transition from the main floor, separated by a form partially filled with concrete from the pour of the main level walls, to the lower gravel subfloor cleaned up. That just involved breaking off the foam, cutting the plastic ties, chipping out some dried concrete and smoothing everything off to avoid any sharp drops that could stress the concrete.
Once that was ready, we laid sheets of extruded polystyrene foam flat on the gravel, cutting out notches and knockouts around all the plumbing and vents. The primary purpose of the foam is to prevent you from heating all the gravel in the subfloor, and keeping the heat in the concrete slab where you can feel it. Compared to everything else it was surprisingly easy, and within about an hour and a half it was all covered. To provide a surface to attach the pex tubing to we then cut strips off of a giant roll of rusty metal mesh. These each had to be bent backward to straighten them out so they would lay flat. Once they were laid atop the foam sheets, we just unrolled the bright orange tubing and attached it in two loops in rows about 18″ apart with plastic zip ties.
After clipping off all of the zip tie ends, the last step was to get the floor lights (a chain of three of them underneath the master bedroom hallway window) installed. We got quite lucky in that the lights were at the perfect height (level with the top of the floor) when they sat on extruded polystyrene foam boards. To hold them in place, we ran the plastic conduit underneath the metal mesh with the light boxes sticking up.
It sounds like a fairly straightforward process, but I’m quickly learning that most tasks take about thrice as long as originally expected. By the time we finished it was about 10:30 and we were working in the light cast from some temporary lights. The concrete trucks were coming first thing the next morning, so it was definitely worthwhile.
