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Community and Q&A

Covering exposed glass fiber insulation in basement ceiling

ChrisJS | Posted in General Questions on

My new house has an unheated basement ( typically 5-8 degrees less than living space) with exposed fiberglass insulation between the ceiling I-beams. The concrete walls are not insulated.
I do not plan to “finish” the basement but would like to put some exercise equipment down there, and am concerned by the potential health risk from inhaling FG fibers. I am searching for ways to cover the exposed FG without putting up a drop ceiling or drywall.
I considered Tyvek stapled across the beams but would much prefer not having the Tyvek logo all across the ceiling. Have also considered non-woven polypropylene, FSK (foil/craft paper)., and plain aluminum foil. I would appreciate hearing from anybody who has solved this relatively common problem. One concern (how critical??) is about creating a 2 vapor barrier “sandwich with craft paper against the sub-floor and aluminum foil facing the basement with FG insulation between.
Considering the small temperature gradient, not sure this matters, especially since I do not see the ceiling cover as being particularly “tight”.
I am also considering insulating the bare concrete walls with exposed Dow Thermax but am waiting for the OK from my local building inspector who needs confirmation that Thermax meets national IBC/IRC codes. I know others have used this material. Were there problems getting local approval (in Massachusetts)??
All input much appreciated.

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  1. Dana1 | | #1

    If the basement doesn't dwell below 40F for weeks on end in winter (the approximate dew point of conditioned space air in a moderatly venitlated house), you don't have to worry about the very low vapor permeance of the foil facers or FSK at ALL.

    If you basement is getting that cold it either A: leaks a lot of air and/or B: has no foundation insulation, both of which are fix-able, and should be fixed- especially if there's a furnace & ducts or boiler & plumbing down there, even if you're not planning on finishing the basement. Simply insulating the basement walls raises the temperature several degrees, lowering the mold risk throughout the basement.

    If you're the type prone to worrying about it despite everything else, using a perforate aluminized fabric type radiant barrier would run about 5 perms (comparable to latex paint on gypsum board), and the perforations are small enough to filter out fiberglass fibers.

  2. ChrisJS | | #2

    Thanks, D.D.
    House is LEED tight and "unheated" basement is only about 8 degrees below living space.
    So will consider using the FSK or alum. foil. to cover the FG.

  3. Andrew_C | | #3

    This is just an opinion, but nothing good comes from overhead fiberglass batts in the long term. Since they don't appear to be doing much from an insulation standpoint, I'd just remove the fiberglass. Especially if you plan to insulate the walls, which should make a noticeable difference in comfort and air quality.
    I've always found that an "closed" basement ceiling becomes a hassle at some point, when I want to run a cable, put in an outlet, set up a net for hitting, install a pulley system for home gym, etc. Having easy access to the floor joists and underside of the floor is nice.

  4. Dana1 | | #4

    If it's radiant floor heating on the first floor the joist insulation would be needed, but with a code-min R15+ foundation walls and an R8 slab it's not really doing much of anything.

    My central-MA foundation walls are insulated, the slab isn't, nor are the joists with the exception of one ~250' radiant floor zone. The boiler & HW heating is in the basement, and with a 68-72F first floor it never drops below ~65F there no matter what the outdoor temperature happens to be. If I insulated between the joists everywhere it would drop a few degrees in the basement, but if the slab were insulated it would be few degrees warmer.

  5. GBA Editor
    Martin Holladay | | #5

    I'd like to add a vote to the suggestion that you insulate the basement walls and remove the fiberglass batts from the basement ceiling.

    For more information, see How To Insulate a Basement Wall.

  6. charlie_sullivan | | #6

    If you are concerned about breathing fiberglass fibers, I think the process of taking them down would result in more exposure than leaving them up and covering them. I like the idea of the perforated radiant barrier material, because it would actually be one of the few places where a radiant barrier does some good. But you can also use tyvek, with the logo side up, or get plain white tyvek that isn't sold for building purposes, e.g.

    I've always found it a little surprising that code doesn't require drywall on a basement ceiling for fire protection, and am thinking about a drop ceiling in my small utility room that is the only unfinished area of my basement for that reason. I'm curious what others think about that.

  7. Andrew_C | | #7

    Charlie - don't you think you'd have less exposure if you covered up (mask, gloves, disposable painting suit) and removed the insulation in one go, rather than go down in the basement without protection on a daily basis for a long period of time?

    I'm not sure if a drop ceiling adds any fire protection or not. Aside from that, I haven't seen very many drop ceilings that looks good. I'd rather spray the basement ceiling all black or all white, similar to commercial/restaurant spaces. (Probably all white in a basement that typically doesn't have sufficient lighting.) Your $0.02 may vary.

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