Sealing above an exterior crawspace


Old 04-14-18, 12:51 PM
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Join Date: Jun 2007
Posts: 101
Sealing above an exterior crawspace

I have a room built out on pilings. The underside has some shelter from the elements but is otherwise pretty exposed.

The storm surge from Superstorm Sandy destroyed everything under the room (insulation, etc.). Among other steps I had a contractor insulate underneath; he used fiberglass rolls covered (below) with foam sheets nailed to the joists.

Two problems:
1) the guy the contractor sent didn't do a great job. He missed insulating some areas (mainly at one end of the crawlspace, where two beams were set about 6" apart and he forgot to stuff insulation in there).
2) some months later I had the AC system replaced (also Sandy-destroyed) and they redid the ductwork underneath. So where they removed and ru-hung the ducts there's now a big gap), and they did a halfway job replacing the insulation sheets where they took them down and put them back up.

I don't think I need to tear everything down and start from scratch, but I'd like to make everything more draft proof. We get some pretty fierce winds down here; I've done what I can to protect the space from the worst of it but it definitely needs more protection. (the space used to be fully open on three sides; on the two sides that have an attached deck I hung tarps underneath between the deck and the room, blocking the wind, and built a skirt on the fourth side of the room.)

So what else can I put up under there? I was thinking maybe Tyvek but that's technically not what it's meant for and I wasn't sure if I was going to give myself other problems in doing so.

In the attached pictures, the first image is the biggest problem: where the duct is and the poor state of everything there. You can see a different type of board just above the duct--that's where the old duct had been, and the guy who put in the new insulation just ran the foam board up to where the duct had been. When the ducts were removed, the old board (a sort of cardboard-like material) was left exposed. If I were to use house wrap my thought had been to enclose the duct, too.

Second image is a general look at the space, and the last is the space between the next two beams, which is in better shape.

Any thoughts about fixing this up?
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Old 04-14-18, 01:05 PM
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I would recommend you finish off the insulation and foam first, if your havent already... this isn't rocket science, it's surely something you could DIY. Clean out all the crap on the ground and put some 4 mil poly down on the ground to make it easier and cleaner to get around.

Adding Tyvek would not help or hurt. I would not recommend you use it as I would say its a waste of time... it doesn't help with what I see as your main problem... keeping critters out. If I were you, i'd get some sheets of osb and shoot them to the bottoms of the joists with a siding gun. After you do the bottoms of the joists, come back and add a 2x2 or scrap strips of osb to the perimeter of the ductwork, and the perimeter of the beams to close any gaps. If you want to make it a little more airproof, caulk the seams when you are done.

You should be buying vinyl skirting, like what they put around a mobile home, to finish the outside perimeter of the crawl space. It's not completely air proof but it's better than nothing and will slow the wind down 99%.
Old 04-15-18, 11:53 AM
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Join Date: Jun 2007
Posts: 101
Thanks for the reply. We don't really have critters around here. There's the occasional cat running around, and the squirrels have never been interested in the place.

The fiberglass insulation is pretty much OK; the biggest problem is in the section with the ductwork, where not only is there the gap above the duct (which DOES have fiberglass above it, just no foam board) but in other parts of that section, where the foam board is ill-fitting. You can see all this better in this other picture I attached below.

There are several sections at issue here: three large ones (six to seven feet wide). Two of them are mostly OK (see the third pic in my first post) though the seams definitely need work--they'd just been covered with duct tape, which hasn't held. and where they join the foundation wall wasn't sealed, either.

The third large section is where all the gaps are; there's fiberglass above, but the foam board below is a mess. FWIW, the material is some material that seems like a combo of felt and cardboard (see second attached pic). I can't put any foam board in its place above the duct because I'd have to way to attach it without removing the duct.

There are also smaller spaces, about 6" wide, between the double-sets of joists that separate each of the above sections. The guy who did the install forgot to insulate over/between the small space between the far set of joists; the pipes there froze that winter, before I found it. I filled the space with lots of insulation.

There are two problems with using OSB: the duct hangs below the joists--the duct drops 12" as measured from the foam boards while the joists drop 9". So I can't put boards across from joist to joist--the duct is in the way. Also, the ground slopes up towards the foundation, and in the last six or so feet there's only 6-7" clearance; I don't think I could fit to attach the boards up in that area. I can fit between the joists there, just not under them.

The last pic shows what I have between the room and the deck (hidden from the outside). I used plastic tarps because the section is so irregular; it would be almost impossible to put skirting in.
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Old 04-15-18, 11:56 AM
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FWIW, this is that last little section where the guy had neglected to insulate and I later stuffed in the fiberglass.
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Old 04-16-18, 08:02 AM
Join Date: Jan 2010
Location: North East Kingdom of Vermont
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I had to do a double-take; but I guess this is Sealing the Ceiling !

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