Reclaimed XPS insulation question
Howdy everyone, I’m new here.
I took the plunge this week, without knowing any better, and got my hands on 60 sheets of reclaimed 2′ x 4′ x 4″ of Dow Roofmate R20. I got them at a decent price in my area but not decent enough that I can simply throw them away. I bought those to insulate my off the grid cabin’s roof (on the inside). Now, of course, come the questions I should have asked before…
1-how much are the cracks and holes in the board affecting insulation? (see attached picture – they are beat up on one side and perfect on the other side).
2-variability in weight – it ranges from 6 to 24 lbs / sheet (!). They average 12.5 lbs / sheet. Most likely absorbed water (?!) so here are the sub-questions:
a)does this affect insulation? Are some so soaked I should throw them away? They all feel dry to the touch.
b)can I / should I try to dry them? Right now they are in my basement with a fan and dehumidifier running 24/7. Room is at 77F and 43 humidity…it seems I can’t get the room any drier.
c)in the event I can’t get out all of the water, will that generate enough moisture once installed that it’ll ruin my roof rafters over time?
Thanks, that’s a lot of questions !
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Replies
XPS that is labeled R20 will not perform better than R17 once it's climate damaging HFC blowing agents have dissipated ( after a few decades of service), even if it's in perfect shape, with no accumulated moisture. From a design point of view treat it as R15-R17, but only after you've dried it out.
It will dry out eventually- heat + ventilation helps. Get them OUT of the basement, where it's cool and not very dry. Building a small hoop-greenhouse "solar kiln" to store it in over the summer can probably purge most of the moisture before winter.
The most common XPS is "Type-II", or 1.5lbs per cubic foot nominal density. Roofmate is nominally 1.8lbs per cubic foot: https://www.aqua-calc.com/page/density-table/substance/styrofoam-blank-roofmate-blank-insulation
So a 2' x 4' x 0.33' sheet is 2.64 cubic feet, x 1.8lbs would be about 4.75 lbs when dry. Even your six pounders are carrying a bit more than a pint of water. I suspect the performance hit is pretty small for those, but most your sheets will have to be a LOT drier to perform at even R10.
Thanks for the reply, I only have 2 months, maybe 3, before I get to the roof part of the project. Is it still worth it to go the "greenhouse way"? My cabin is very remote and I'm kind of concerned that leaving that stuff out there to dry will create one hell of a rodent fiesta. Also, on average in the summer, its way more humid than 43 over there...it's a basement that has the same temperature/humidity than the rest of the house.
Best would be to place the sheets in the sun for a few days and see if they improve. If you orient them vertically with some space between them you probably won’t have any rodent problems. You want the sheets to get hot in the sun, and you want all sides exposed to air for fastest drying. You don’t want to stack them or lean them against each other as that will slow down drying.
Heat and air movement is what you need. If you don’t have sun, setup some box fans to blow air over the surface. You could apace the sheets apart with something like 2x2 strips and blow air into the end of a bunch of sheets spaced like that. The moving air will aid drying.
Bill