Like the floor, I decided to use extruded polystyrene (EPS) rigid foam board insulation in the walls and ceiling. The three factors I liked were: 1) essentially waterproof; 2) good insulation properties; and 3) it doesn't leave as much residual foam dust as regular Styrofoam panels.
The walls and ceiling have room for 1.5" thick insulation so that's what I went with. At 1.5" EPS has an R-value of 7.5. I had to special order it and it took several weeks to arrive.
In the picture above you may notice there are areas where I used 1" EPS instead of the 1.5" EPS.
The wood wall panels that will be installed over the EPS are only 1/4" thick and won't provide a good holding surface for anything needing to be securely screwed to the wall. Cabinets, curtain rods, and lights will need to be secured. to the walls. So I created voids for strips of 1/2" plywood by using 1" EPS instead of the full thickness 1.5" EPS. I used leftover marine grade plywood from the subfloor installation. It has waterproof glue so shouldn't delaminate easily.
You'll also notice that I had to plan and install the electrical rough-in wiring. Most of the wiring will be routed through the cabinets, but some needed to go through the walls so preplanning was required. There will be a separate post on that.
One challenge was the incompressibility of the EPS. It's rated to support something like 15 lbs per square inch, so it doesn't easily compress. This is a problem because in the area of the Z-shaped ribs there is actually slightly less than 1.5" of space, so the foam won't easily fit. My solution was cutting a thin rabbit out of the EPS panels along the edge to accommodate the aluminum rib. This was very time consuming and messy. The foam dust clings to everything and it took quite a bit of vacuuming to get it all up. Below are some pictures of the rabbiting process that worked for me.
I ended up taping all the seams with Tyvek seam tape. This stuff isn't cheap and it took a couple rolls so you might want to consider other options. But it did seem to work pretty well.
If there was one lesson learned that I suggest others consider if they do this, it's this: install the wall insulation and then wood paneling before moving on to the ceiling insulation and paneling. Why? Because the wall panels will not need to be as precisely cut due to the large "reveal" (overlap). This is what they did at the factory. Furniture makers understand this, and I really should have too since that's my hobby, but I got ahead of myself.
But it's done now and I can really tell that it's effective in managing the temperature and radiant heating/cooling.
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