I get to play a game that I know! And the game is called “installing a radiant floor slab”.
And now I get to play with the next four components of the radiant floor slab assembly:
- Vapor barrier
- Welded wire mesh
- Pex tubing
Installing the insulation was a bittersweet process. Bitter, because the four inch XPS boards I used came from the very carefully installed attic insulation assembly, which I had to take down again. Sweet, because I got to reuse the insulation and it didn’t to go waste.
I mentioned that the aggregate base was finished with the correct slopes towards the floor drains. That means that I had to line up the seams of the insulation boards with the slope ridges and valleys. If not, I would end up with suspended and wobbly boards that would crack or break.
I again paid attention to the bond breaks around the future radiant floor slab. A bond break is a piece of vertical insulation that will thermally separate the concrete floor from the adjacent foundation wall and footings. This assures that the heat in the radiant floor slab is effectively transferred into the room and not syphoned off into the foundation wall or other thermal mass structures.
Vapor barrier and wire mesh
Even though I had an effective capillary break with the open graded aggregate base, I still needed an effective vapor barrier under the concrete floor slab. A large 6 mil polyethylene sheet would do that job. I carefully cut it to size and fit it around the sump, floor drains and footing. To prevent it from shifting around while installing the welded wire mesh, I taped it along the edges.
The radiant floor slab will be heated with hot water. To get the hot water into the slab, I used ½ inch PEX tubing, which I attached to the welded wire mesh with zip ties.
I opted for two heating zones. Zone number one is heating the future workshop to the west. Because this section needs to be kept reasonably warm, I spaced the PEX tubing six inches on center along the edges and 12 inches on center towards the center.
Zone number two is the eastern half of the space and just needs to be kept above freezing. For that reason I spaced the PEX farther apart. I also made sure avoid PEX tubing in areas where I need to anchor into the future concrete floor, such as under the future steps and bottom plate that separates the workshop from the rest of the space.