Ceiling options on rigid foam board

Old 11-01-15, 12:20 AM
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Ceiling options on rigid foam board

I have built a wine cellar. Well let me back track. I'm making wine at home and initially needed something to keep my aging wine cool, but it didn't need to look good. So my wine cellar is more of a walk-in refrigerator I built in my garage. It is an 8' x 8' x 8' cube (basically) with a door and an air conditioner to keep my jugs of wine at 55 degrees.

But I always had the idea that I could finish this off into a proper, nice wine cellar. I can change my basic fiberglass door into a fancier one, put hardwood flooring over the plywood subfloor, and put T&G walls & ceiling. The only thing I'm not sure about is the ceiling.

The cellar is basically a box built from rigid foam insulation (total of R26). Each wall is basically 4 4x8 2" foam boards sandwiched together (2 horizontal sandwiched with 2 vertical). These 8'x8' walls are then assembled into a big box, sealed etc. and have a vapor barrier wrapped around, then simple 2x4 framing all around. I have an exterior door (fiberglass) from Lowes.

So the inside is all foam board - no exposed studs or wood. I can of course drill through the insulation to the studs but would prefer not to.

The interior dimensions of the ceiling are 88" x 88".

Is there any kind of wood paneling, flooring, etc. that I can use that can make a ceiling in this box without needing to drill through the insulation?

It can be supported on the ends with whatever I panel the walls with - Perhaps I could even use 3/4" T&G flooring on all the surfaces. I can also use liquid nails or some other adhesive between the ceiling boards and the foam board. Liquid nails claims to be suitable for adhering porous materials to foam board.

Give the that this is a small space, would a ceiling like this be self-supporting (with some help from liquid nails)?

The only thing that would be attached to this ceiling would potentially be a light weight lighting fixture.

This is un-attached so I'm not concerned with being code compliant. But I also don't want to waste a bunch of money on a ceiling that will sag/fail in a couple years.

Old 11-01-15, 02:45 AM
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I'm not concerned with being code compliant.
You should be as it is for YOUR safety, the inspector is only there for a few minutes but YOU (and your family, if any) are there a goodly amount of the time.

Unless your "foam" is rated/listed for use without a fire resistant barrier then you have a fire trap. I personally would not have built it but if I had I would have done so in a manner that allowed facing both the inside and outside with a minimum of 1/2 inch thick drywall.

You could make a wooden ceiling glued to the foam with the proper adhesive and additionally supported by wall panels as long as it was continuous from one wall to the opposite wall and it would probably not fall. Adding additional support from the floor in the center of the ceiling would make it more secure.

Last edited by Furd; 11-01-15 at 04:28 AM. Reason: Correct misspellings.
Old 11-01-15, 04:07 AM
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Each wall is basically 4 4x8 2" foam boards sandwiched together
Why do you have 8" of insulation on each wall? I make wine, too, but don't have to go to all that trouble to keep it temperate. How are you introducing 55 degree air? Is it controlled? As Furd says, you will need to cover the foam with a fire retardant covering, regardless of code. I just don't see how you will accomplish that through so much foam.
Old 11-01-15, 06:09 AM
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Hi Eric,
As suggested, you should get the blessing from your local code official. Sketch up what you have and want to do and ask if a thermal barrier would be required. If it is an attached garage they may require the foam be covered with an approved thermal barrier both inside and outside. But the local code official is the one to make that determination. heck, s/he may like wine.

Here are some thoughts:
Are your wall actually 4" thick vs 8" as stated. The r-26 corresponds to 4 1" layers of r-6.5 polyiso. If 8" then it would be r-3.25 per inch and I don't know of a rigid foam that low in r-value.

What's under the plywood sub-floor, concrete or the same rigid foam as the walls and ceiling?

You will need some form of air exchange. Completely sealed mold will find a way to grow.


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