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shop ceiling insulation

DennisS | Posted in Energy, Heating & Insulation on January 19, 2005 07:36am

Greetings everyone –

When I built my workshop I didn’t anticipate how cold it would get here in Skagit County WA. especially in Jan/Feb. Bad on me. That said …

The roof structure is exposed trusses 24″ oc with 1/2″ OSB sheathing and snap lock metal roofing. I’ve got a nice Fisher wood stove in one corner of the 24 x 40′ space that manages to keep the shop at around 55 degrees with the OS air at around 32. Walls are 6″ which I’m inuslating and applying 1/2″ OSB to the interior.

Question ….

Is there a rigid insulation that can be applied to the underside of the roof sheating between the trusses? Polyiso or other ‘plastic’ foams are out since I don’t want to live with the fire hazard. I’m considering Fesco Board since it’s fairly easy to handle. The roof is a double pitch style with a continuous clerestory. What would be considered the attic space, that occupied by the trusses will be left exposed …. no ceiling. All electrical and air lines are exposed for easy access and the inevitable changes. Thus I’m looking for a type of rigid board insulation that would fit between the truss rafters.

Years ago I used some tectum on a project but my research so far reminds me that 1) it’s a wood based product – potential fire problem again and 2) it’s primary use is accoustical and not thermal insulation.

Thanks for any comments suggestions.

………..
From Beautiful Skagit Co. Wa.
Dennis
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Replies

  1. steelbuddha | Jan 19, 2005 03:34pm | #1

    How about some foil/bubble sandwich stuff, like Reflectix or Astro-E? You can staple it in between the trusses, and you get good R-value in addition to an excellent radiant barrier. Some of the manufacturers have a 24-inch-wide product with staple tabs on the edges, which would probably be just perfect.

    Tek Supply (http://www.teksupply.com) has a big selection of foil insulation products, and their prices are as good as any I've seen.

    -Jonathan Ward

    1. DennisS | Jan 21, 2005 07:02am | #3

      Thanks for the suggestion, Buddha. I hadn't heard of that stuff before. I'll check it out............
      From Beautiful Skagit Co. Wa.
      Dennis

    2. TJK1141 | Jan 21, 2005 08:47am | #5

      That's what I put up in my shop - 24" wide foil/bubble/bubble/white poly -- with the white side down. The ceilings are 10 feet, and the bubble is stapled to the bottom of the trusses. Seams are covered with white tape, and it looks decent enough. The horizontal seam at the top of the wall is taped and I added a small molding all around to give it a finished look.The shop walls are insulated with regular R-11 fiberglass batts and I used melamine panel-boards for the finish cover. These are easy to clean and don't ever need painting. The electricians set all my boxes for drywall though, so I had to move them back because the melamine panels are only 1/8 thick.The ceiling isn't R31, but 30K BTUs of propane heat keep the whole shop comfortable at outside temps down to 5F. Our Summers here are hot (105F) and dry and that's where the foil makes a big difference. During the first Summer, the ceiling wasn't up yet, and the heat radiating from the bottom of the roof sheathing made it feel like standing under a broiler. After the reflective layer was in place, that radiated heat was totally gone.

  2. BarryO | Jan 19, 2005 08:49pm | #2

    'got the same problem; going to tackle this summer.

    The foil/bubble stuff has some pretty low R-values, it seems to me (it has to, being so thin).

    What about fiberglass?  Use the plastic-backed stuff they use commercially, or Manville ComforTherm plastic-backed bats.  Either of these are rated OK for exposed use, unlike Kraft-backed bats.

    1. DennisS | Jan 21, 2005 07:07am | #4

      > What about fiberglass?....I've been considering the idea of putting up unfaced batts between the trusses then running tie wire across for support. I wonder how this would work with the inevitable dust in the air in a wood shop? Or a constant shower of FG fibers falling from the ceiling onto my freshly lacquered or (worse) varnished projects? (grin)I'm really leaning towards Fesco Board at this point. Not the highest R value per inch of thickness but reasonably rigid and easy to handle and place............
      From Beautiful Skagit Co. Wa.
      Dennis

      1. BarryO | Jan 22, 2005 10:46am | #6

        I think you need a vapor barrier in our climate, so unfaced isn't a good idea.  Water vapor permeating through the the insulation and hitting the cold roof deck and condensing:  Not good.

        1. DennisS | Jan 25, 2005 07:28am | #9

          Barry -The moisture barrier is indeed a concern. The trusses have screened blocking between them so I could conceivably use some sort of rigid insulation held away from the underside of the roof deck to allow ventilation. The more I think about it, though, the less enthusiastic I become about trying to insulate the shop roof. I recently installed a wood stove to take the chill off. I found during a cold spell a few weeks ago that in sub freezing weather, with the walls only partly insulated and drafts from every imaginable crack and opening, I could maintain a decent working environment using not much more than the scrap wood generated in the shop. Given that I plug up some of the holes so I'm not working in a box made of swiss cheese, and finish insulating the walls, I think given our mild climate I'll be better off to spend the money for insulation on more tools! (grin)Anyway, thanks to everyone for the comments and suggestions. ...........
          From Beautiful Skagit Co. Wa.
          Dennis

          1. DanH | Jan 25, 2005 05:33pm | #13

            Another option is just an air barrier up in the ceiling. Plastic or Tyvek or some such. Eg, if you scabbed in pieces between the truss cross-members to give you about 10 inches from the roof, then stapled plastic to that you'd probably cut heat losses through the roof by half.

      2. davidmeiland | Jan 22, 2005 07:44pm | #7

        I'm not far from you and am thinking about the way to handle the same issue when I build a shop later this year. The best solution I can come up with is to insulate over the roof deck rather than between the trusses. If you don't want to cover it, your insulation options are limited. The typical unfaced foam board (and the spray-in variety) has to be covered with rock. When I've seen FG left exposed in warehouses it's always the foil faced type, so you may want to look into that.

        The issue of fire retardant foam board came up in another thread. I don't think anyone identified a source for it, but I believe it exists. A supplier than handles commercial insulation products would be the one to ask. Someone in Seattle, I'm sure.

        The OSB sheathing on the interior will be a major fire hazard. Any chance you want to rock instead?

        1. DennisS | Jan 25, 2005 07:33am | #10

          David ....Would that I had thought of insulating the roof deck when I was in the formative stages! My OSB roof deck doesn't pose much of a fire hazard since I have a pretty high ceiling. I'm extremely careful handling or dealing with volatiles and had my wood stove professionaly installed, plus I keep a close eye on it when it's burning. I'd not like to lose my 'home away from home!'Good luck on your new shop!!By the way, I have yet to get it operational but when I poured the slab for the shop I installed PEX tubing for RFH. Plan on retrofitting a heat exchanger to the wood stove, scrounging some tanks for mass heat storage. Even if you don't get around to it right away, the PEX tubing isn't terribly expensive and you can install it yourself, "just in case" some time in the future ................
          From Beautiful Skagit Co. Wa.
          Dennis

          1. MisterT | Jan 25, 2005 01:59pm | #11

            How about spray on foam? 

            Mr T

            I can't afford to be affordable anymore

          2. davidmeiland | Jan 25, 2005 05:23pm | #12

            My comment about the OSB fire risk was re the interior sheathing you're going to add to the walls. Room-and-contents fires become structure fires when given easy access to the structural members. I still say rock the walls.

  3. DanH | Jan 22, 2005 10:49pm | #8

    With a metal roof you need to fairly tightly seal (and maybe ventillate to the outside) the area between the face of the insulation and the metal to keep moisture out of there. Othewise it will fill up with condensation. Foam type insulation attached to the bottom of the roofing will allow moisture to get in at the edges and collect there. Something that can be fairly tightly sealed across the lower face of the upper truss members would be better.

    (Actually, what would be ideal for this would be a sort of poor-man's scissor truss. Basically a regular truss with fillers inserted about 8" below the top surface, so that nailers could be attached to the sides and some sort of wallboard inserted. Would give you a tight seal and room for both insulation and ventillation, but would still allow the use of the "attic" area for storage, wires, etc.)

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