January 1st, 2020

Ann Vole

Sideways insulation and glitter

I had the idea of putting insulation batts 90 degrees from the normal way they are added and then use glued-on tar paper or something similar to actually attach the two surfaces of the insulation layer together. The problem I needed to deal with was trying to put an air barrier at the 2/7ths inside R-value and 5/7ths outside R-value point of the wall while the framing is at the 3/4 inside R-value, 1/4 outside R-value point. The idea I just came up with is to do exactly that but with two courses of the sideways insulation. I can also leave the area between the studs and the air barrier empty and put higher R-value insulation between the stud and the outside air gap between the weather barrier and the sheathing so the studs stay above freezing on the coldest design days. Lets use R-98 for the walls for easy math:14 x 7. This means the inside-the-air-barrier insulation is R-28 (2/7 of 98) or 1/2 of a batt of 16"-on-center batt width (14.5") of R-4-per-inch mineral wool insulation (R-29 if you include the 1/4" of the 7.25" half-batt). Outside of that will be R-70 or 17.5 inch wide batts of mineral wool put inside and outside the studs and specifically through the stud gaps. The tricky part of this would be metal bracing straps on the studs to prevent racking that will have to be fitted through these sideways batts. Another option is to have 3 courses of sideways batts all outside the stud cavity so 70-25 for R-45 between studs and inside air barrier or 11 inches of mineral wool... 24"-on-center batts are 22.5" so half batts will do and 6" on the outside of the studs (R-24... 1/4 inch mineral wool is an extra R-1 for R-46 on the 11.25"). I want air gaps inside and outside between the insulation and either the sheathing or the inside wall for drying but I would also like this gap to be a radiant barrier that is vapor open. This is where the crazy idea of glitter comes in... paint the surface with a vapor-open weather barrier paint then glitter-bomb the wet paint to make a vapor-open radiant barrier. Note that I have an alternative method of replacing the structural strength of sheathing that may even stop bullets: put OSB or plywood or solid wood bracing BETWEEN the studs then fill the stud cavity with foamed concrete to make "aircrete". This will be enough structural addition to keep the bracing from moving or buckling under load, provide some extra bracing itself, prevent the movement of pests, be an extra vapor-open air barrier, and protect the wood from fire and pests and possibly mold (undesirable pH for mold). This also doesn't stop me from adding the metal bracing that is building-code-approved replacement of sheathing. Note that if all the metal is at the same temperature due to having the same R-value inside and outside the metal, there is no heat difference to conduct so no thermal resistance loss. With a few extra R-value points from the aircrete, I can reduce the outside 6" to 1/3 of the 14.5" 16"-on-center batts or slightly short of 5". This is needed because I assume I only have 6" outside the studs to work with on one side of the building so I need a half-inch air gap and at least a half inch for siding of some sort (magnesium oxide boards are a possibility)