I’ve got a stack of Manville Fesco Foam insulation boards salvaged from a commercial installation that I’m repurposing for the inside of my garage roof. I’m planning on machining them to fit around the joists in order to preserve some headroom without sacrificing too much performance in terms of LTTR.

Since I didn’t salvage them myself, I didn’t see how they were installed. So the questions are:

  1. Which side faces the interior of the building - The black side or the perlite?
  2. Can I use screws or nails with washers to attach them to the joists, or would that sacrifice too much performance? I.e., should I use something like construction adhesive?

Photo of a stack of insulation boards Photo of the label, provided by the guy who sold them to me

  • what does the manufacturer's website say? – jsotola Dec 29 '19 at 2:54
  • That’s the thing - I haven’t been able to find the actual instructions there. Maybe I missed it, but I don’t think so. – Bill Horvath Dec 29 '19 at 6:29
  • AFAIK, that type of panel is usually put on top of the roof, with the "cement" side up for (light, maintenance) foot traffic. Sometimes (often?) above the actual waterproofing layer. – Ecnerwal Sep 28 at 15:25

The J-M Fesco data sheet shows the black TopLoc layer on top, with a glass reinforced facer on the opposite side.

The data sheet I saw didn't give many installation details, but I doubt a few fasteners with large washers would have a large impact on your thermal performance as long as they only cover a small percentage of the total surface area. Focus more on getting tight connections between the sheets and eliminating air leaks.

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  • Thank you!I saw the data sheet you’re referencing(?) at jm.com/content/dam/jm/global/en/commercial-roofing/…), but I found it really difficult to interpret. The black side is very thin, and adheres directly to the foam. The other side is the ½ inch thick perlite, and it’s a light grey in color. In the diagram I saw, the TopLoc is on top of (outside) the perlite, but on the panels I have, it doesn’t look like there’s anything there. I suppose TopLoc could be a clear spray-on coating or something along those lines. – Bill Horvath Dec 29 '19 at 19:11

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