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Old 05-29-2017, 08:58 AM   #1
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Covering exposed fiberglass insulation in unfinished basement


I have a large, relatively dry unfinished basement I would like to make more clean, pleasant, and usable (storage and an exercise area) by painting the concrete walls, concrete floor, and "ceiling" (exposed plywood, joists, and ductwork). While I would love to finish it for real one day, that day is at least 5 years off. So in the meantime...

My question is: how should I cover the pink fiberglass insulation that is wadded between the joists above the concrete walls? (photos attached)

[**EDIT - the 2nd photo mysteriously attached upside down. It's correct on my computer, and i can't figure out how to flip it within the post. So the wood at the bottom is really the ceiling, just to orient you.]

I think it would be relatively easy to cut pieces of wood to fit in those spaces between the joists to cover the insulation. And for the wall running parallel to the joists, I could nail a piece of wood to the bottom of the joist so that it spans the gap between joist and wall with the other edge "sitting" on top of the concrete wall.

But after hours upon hours of googling and reading, I'm a bit confused about what is/is not safe and allowable for moisture and fire code reasons. At times, I feel like I read directly contradictory information.

Would it be ok, from both a moisture and a fire safety standpoint, to cover the fiberglass in the way i described with the same type of wood as the joists? If not, would it have to be drywall? Any other better ideas? I'm a relative novice trying to learn, so please dumb down any answers as necessary.

Thank you so much for any help!
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Covering exposed fiberglass insulation in unfinished basement-image1.jpg   Covering exposed fiberglass insulation in unfinished basement-image2.jpg  

Last edited by Depice; 05-29-2017 at 09:03 AM.
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Old 05-29-2017, 09:23 AM   #2
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Re: Covering exposed fiberglass insulation in unfinished basement


Hi Depice and welcome to the forum.
First, where are you? Your climate region helps us advise on how best to address those cavities and the concrete.

Your explanation sounds fine to me. I don't see either a fire blocking issue or a moisture issue. The key avoiding any moisture problems is to be sure that covering is air sealed so no basement air can reach a cold surface. How cold is a climate question.

A more common approach would be to use rigid foam board but that creates a fire code issue where the foam needs a thermal barrier. One brand of foam has been approved to be left exposed because it has a thick (and tested) layer of foil, Dow Thermax. It's hard to find in some locations but nice to complete the job in one step.

"At times, I feel like I read directly contradictory information." Isn't the internet wonderful, it provides all the information you need but doesn't tell you which is correct J

If you are in a cold climate with significant heating bills then some additional rigid foam board over the exposed portion of those walls can make a huge difference in heating costs. We can discuss the code and benefits after I know where you are.

Bud
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Old 05-30-2017, 06:25 PM   #3
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Re: Covering exposed fiberglass insulation in unfinished basement


Bud,

Thank you so much for your thoughts! I'm in the Philadelphia suburbs, so fairly cold winters and hot summers.

My initial idea had actually been to use foam board insulation cut to the right size to cover the fiberglass, but then after I started reading it seemed like that might not be a good idea for moisture reasons (but I'm not really confident I was understanding everything properly).
so then I thought just covering it with wood wouldn't be much more difficult and would leave a better surface to paint (planning to spray the concrete walls and exposed wood ceiling to make the space a bit cleaner and brighter), but I couldn't find something I felt was a definitive answer about whether covering with wood would be acceptable. And then I started seeing stuff about fire code requirements and just became more confused the more I read

I really appreciate you taking the time to reply with your knowledge.
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Old 05-30-2017, 08:02 PM   #4
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Re: Covering exposed fiberglass insulation in unfinished basement


There are two sources of moisture at the rim joist level, assuming the folds don't get that high. In the winter a cold surface will take the basement air below the dew point and result in condensation. That situation is what you currently have where air can move through the fiberglass and reach the cold rim. I've seen ice there many times.

The summer moisture issue occurs when humid outside air reaches a cool inside surface, either due to air conditioning or just the cool basement walls. The rim area is usually not a concern.

But both situation involve the movement of air which can carry lots of moisture. Some small amounts of moisture can move through the rim but as long as they can dry to either inside or outside tho9se tiny amounts pose no concern.

Your use of wood would be acceptable and avoid the need for a thermal barrier, although it adds no extra insulation value.

As a note, the above grade foundation that is exposed to the cold weather is a major source of heat loss. A basement may feel reasonably comfortable due to unintentional heating from the central system but never the less there are a lot of BTUs flowing to the outside. In my reference material they list an 8" concrete foundation as being about the same as a single pane of glass. That is just short of an open window.

The orange box store lists the Thermax as a special order and although I have never ordered any the last time I checked the 1" material didn't require an entire truck load (just kidding), but there are minimums. An added advantage of the Thermax is one side is white as opposed to shinny foil. Now, if you added say 4' of rigid from top down you would probably be covering most if not all of the exposed exterior and adding r-6 to r-1 would greatly reduce that heat loss.

Before I forget, before you close off those rim cavities be sure to caulk the inside perimeter and any penetrations plus the sill plate to foundation.

Bud
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