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Community and Q&A

Workshop shell-in for part of a steel building

knobhead | Posted in Energy Efficiency and Durability on

Plans are to shell inside of new steel bldg for work shop…. if I screw polyiso to bottom of rafter,
(to limit thermal transfer there), then screw steel to that as shop ceiling, I would then flash with 1-2 ” foam, filling the remainder with densepack blown in,
OR just blown in only densepack to top of rafter,( 6″ depth, I believe)…..

The question is… I leave blown-in open to the inside atmosphere at top of fill, possibly netting blown-in for stability, or do I lose r-factor leaving it open, Do I somehow need to seal top of rafters, … around scissor connectors?
If necessary, what product would be best?
steve B.

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  1. GBA Editor
    Martin Holladay | | #1

    It never makes sense to install any kind of insulation between steel framing members, because steel studs, joists, and rafters act like thermal bridges that steal 85% of the R-value of any product you put in between the steel framing.

    If you want to use steel framing, the only type of insulation you can use is a continuous layer of rigid foam insulation on either the interior or the exterior side of the steel framing.

    Of course, if you are willing to switch to wood framing, it's possible to use cellulose or blown-in fiberglass between the framing members.

  2. knobhead | | #2

    sorry Martin, as usual, I'm not detailed enough....btw, I'm zone 5, and the interior is wood rafters, so I considered screwing same material, steel, facing the shop floor, and a layer of foil iso between steel and rafters, then fill remainder of rafter with blown in, but do I need to cap top of rafter with netting or another product to "hold" blpwn-in in place. In this scenario, IS steel acceptable as "ceiling only" surface?

  3. GBA Editor
    Martin Holladay | | #3

    Q. "Do I need to cap top of rafter with netting or another product to "hold" blown-in in place?"

    A. No.

    Q. "In this scenario, is steel acceptable as "ceiling only" surface?"

    A. Yes.

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