The Walls Are Closing In On Me…
Yes, I am starting to close up the walls. Mostly that involves filling the bays between the 2 x 2 studs (actually 1 1/2” by 1 1/2”) with R-Max foam board and then putting 1/2” plywood on top. It’s mostly pretty simple, tedious and slow, but simple. I do have a few notes along the way…
My favorite tool for doing this is a long thin bladed bread knife with a scalloped edge. The long blade is best for making long straight cuts. The thin blade is good for slicing through the foam cleanly without digging out a kerf the way a saw blade would. The scalloped edge helps to keep the knife sharp and also gives it a little teeth for back and forth sawing when necessary. I don’t usually use the blade perpendicular to the material, but instead lay the handle at a shallow angle and pull it down the cut line. The first cut is only 1/4” deep, or whatever is easy. One or two slices after that finishes the job equally well for either the 1/2” or 1” thick foam. The sharp blade leaves a clean, not a crumbly edge, and it cleanly cuts the paper/foil on both sides.
Beyond that, the only other tools required are a tape measure and a Sharpee pen. The usual process is to measure the width of the stud bay, top and bottom, making note of any difference or bow in the studs. Mark out the width and make the cut in the 4’ direction across the 4’ x8’ sheet, or whatever is left of it. It doesn’t matter that a 4’ long chunk won’t fill the bay from top to bottom. In general it is a lot easier to cut and fit smaller pieces than larger ones anyway. Don’t worry if you make a little mistake, as there will be lots of scrap material to fill little gaps.
I am not using any glue, just wedging everything in nice and tight. I also fill the bays to the top, so there is no room for anything to shift or squeak. I doubt that R-Max would squeak (like Styrofoam) anyway. The usual plan is to lay the foam in 2 layers. The first layer is 1” thick and fits around all the conduit. The second layer is 1/2” thick and mostly goes over the top of the conduit, except in places where it stands proud for some reason. Mostly this only happens where conduits cross. In that case I dig out the foam on the back side of the 1/2” layer without breaking the paper/foil on the front side.
Both layers fit around all the outlet boxes. Often times you can lay the foam on top of an empty box and press it into the box a bit. This makes a dent in the foil for easy cutout of the proper shape. In some cases the conduit makes various curves and bends which the first layer of insulation matches closely. Once the boxes are clear, the foam can be smashed on top of the conduit, which makes a clear dent allowing the conduit channels to be accurately cut.
I throw almost nothing away. Even irregular pieces can be fit together to fill smaller spaces. Small pieces of foam are fairly compressible and can be cut and pressed into place. If it all fits nice and tight, it will get the job done. There is no place for air to leak anyway. The FRP (Fiberglass Reinforced Plywood) on the outer walls is inherently air tight so the insulation just needs to break up the convection loops that would allow air to move within the walls and carry heat in or out.
Of course, there are always weird shapes and buried spaces that need to be filled. When all else fails, you can use the injectible foam in a can, but I have been using very little of it. Mostly I just keep stuffing pieces of the R-Max in, back to front, top to bottom, sometimes little weird shapes piece by piece until eventually the space is filled. I am not saying it is the best method, and it may not be that time efficient, but it is what I do. If you were making a living at this, I am sure you would have to find a faster way, like spray on foam, but the R-max is what I have to work with.
I like the idea that I am creating multiple layers of foil to reflect IR (Infra Red) radiation. In some places like the ceiling there will be 4 or 5 layers, with foil between each. I can’t prove that all those layers will produce superior results, but I suspect they will.
As I cover over the conduit, I mark the conduit locations on the foam, and then lightly on the plywood. I want to keep track of where the conduit is so I don’t eventually put a screw through the wall in the wrong place.
I have designed the stud locations so that every plywood edge is supported. I am using 1 1/2” sheet rock screws every foot or so along every edge, and down every stud, along with a bead of Liquid Nails at every interface. I pre drill the holes through the plywood, but not the studs, so the screws will be able to suck the plywood down nice and tight. So tight that the screw heads are pulled well into the plywood even without any countersink. My plan is to fill these divots with non-shrink spackle later. All joints will be caulked and then spackled, but not taped. I don’t expect cracks to develop mainly because everything will be locked down so tight that it will be hard pressed to even move. (We will see though…)
Plywood is an interesting subject all by itself. It seems every home improvement store carries something different. I am using 1/2” plywood on the walls in general, and I want one good surface, but I don’t care if it has beautiful grain, or is ready to accept stain. I plan to use conventional latex semigloss after appropriate surface prep and priming. It seems the available plywood I could use ranges in thickness from .485” to 1/2” and has different surface woods. It also varies in terms of the glue used, and its rating for indoor or outdoor use. I mostly don’t care for my application, but it is amazing the lack of standardization among the different stores. You would think it would be a pretty stock item…
To be continued…
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