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Old 05-08-2014, 12:28 AM   #1
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Crawlsapce Insulation Suggestions

This is an apt and the tenant found that the bathroom was too cold for temperature code this winter. The bathroom was apparently added over a deck at some point. The crawlspace section where it says 'crawlspace wall' is fully enclosed with 4 block walls. The crawlspace on the left of that is three block walls with the front facing wall being just plywood for exterior storage. On top of the block wall that separates the 2 crawlspaces is a band joist represented by the black piece I drew. That band joist blocks air from the left crawlspace to the right side one. But, as shown by the arrow, air gets right though the spaced decking to under the bathroom. The deck has a roof but it doesn't extend past and minor water also got into the crawlspace.

The crawlspace is unvented, has a concrete floor, and is joined to the main basement with a closed/open 2'X2' hole in the wall.

There were only a few random pieces of insulation in the crawlspace ceiling. So I insulated the three perimeter walls of the crawlspace under the bathroom with unfaced R30 fiberglass after sealing any gaps with greatstuff and caulk. I sealed the section of decking where the arrow is with flexible caulk and insulated the crawlspace ceiling with unfaced R30. They tested the temperature after this and it was still a couple degrees too cold to meet code. So I cut some holes in the bathroom wall and found that they had barely insulated it originally. I rented a cellulose blower but it jammed when used correctly, and when it worked, it would just clog up too soon especially if there were a pipe/wire in the bay. Since it only needed a couple degrees to meet code, I put strips of unfaced fiberglass in the holes in every bay except where the shower tiles are and then patched and painted. At this point, it wasn't cold enough outside to test the temperature again. The tenant said that their contractor friend said the crawlspace should have been done with foam boards instead of unfaced fiberglass.

Owens Corning themselves say right here at around 5:20 that an unvented crawlspace only needs the walls insulated and that unfaced fiberglass can be used:

The tenant is mainly concerned about air infiltration and thinks that the spaced decking is the problem and says that 'boards' should be put over the deck. They want foam boards since they're taped together and less likely to leak air even though I had already sealed the entire crawlspace with greatstuff and caulk. I know that the main problem really is that the bathroom walls aren't insulated enough and the only way to fix that is to have a truck-mounted foam sprayer cut in from the exterior and insulate behind the shower walls and all the rest of the bathroom walls. But as mentioned, it wasn't temperature tested after I put strips of fiberglass high and low in every bay of the bathroom except for the shower walls, so it probably meets temperature code as it is.

So what is your take on the unfaced fiberglass? if I put a vapor barrier/retarder over it, isn't it the same as foam boards except that it's actually better because of R30 vs foam boards at around R15? If you think it really needs a vapor barrier/retarder, shouldn't I put one on both sides of the insulation? Because as many have said when it comes to this, single vapor barriers/retarders are only good for the cold/hot season and cause damage for the opposite season - like, if I put a vapor barrier over the fiberglass in the crawlspace ceiling instead of behind it where it would be touching the subfloor, then in the summer, heat from the crawlspace will meet the cold from the bathroom and condense on the outside of the vapor barrier which is okay but in the winter, heat will condense on the side of the vapor barrier facing the joists and moisture will collect in there. Some have suggested a vapor barrier/retarder paint maybe I can paint under the joists with that, put the fiberglass back up and then put a vapor retarder/barrier over the r30, and same for the concrete block walls. But I'm trying to convince them more materials and work is overkill anyway though.

And for putting 'boards' over the decking where I already sealed between all the decking with flexible caulk, can you think anything water and airproof besides something pricey like having a truck mounted fiberglass sprayed installation?

What's you take?

Last edited by calypso121; 05-08-2014 at 12:36 AM.
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Old 05-09-2014, 11:47 AM   #2
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Are they complaining about the floor or the space in general?
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