Questions about fully encapsulation a crawl space
My crawspace I hovering at 80%+ moisture. It needs encapsulation asap.
I am considering doing the install myself. I did get one reasonable quote for 4k(stego crawl 15) and another crazy one for 12k. Both include spray insulation up walls.
The quote for 4k is using stego crawl 15mil, which I would also he using if I Install myself.
They quoted me for 6 inch overlapping seams and 4-6 inches up the wall, with spray foam going up to the joist and in joist bays.
My questions are:
1) how far up the foundation walls should I go. I beleive 6 inches is the minimum. Would it be better to go higher?
2)should I ask for 12 inch overlap? I am concerned about smells or soil gases.
3) Is it dangerous to spray foam the sill plate and joist bay ect. What if there is water intrusion in the future. Won’t spray foam prevent the ability to inspect or catch any issues?
If I leave the sill plates and above uninsulated how will this affect the encapsulation?
This house actually has some dry rot in the sill plates and floor joists. It makes me nervous to cover stuff up with foam.
4) Stego has two size options 14’x100 or 5’x200. Would it affect the quality of my encapsulation using the smaller 5 ft wide rolls? Only the 5 ft is readily avaliable locally.
5) What else should I be aware of? What should I ask the contractors to make sure they are going to do a proper install?
Thank you,
Josh
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Replies
Josh,
I would deal with this one issue at a time.
Your primary concern is humidity in the crawlspace., which is coming though the ground underneath, and the concrete foundation walls. I would suggest:
- Cover the floor and the entire concrete portion of the crawlspace walls with poly. See how much that on its own reduces humidity. 6" overlap is fine. The joints all need to be taped, as does the perimeter. The advantage of wider rolls is less joints to open up when you move around in the space in the future. This is definitely something you can do yourself relatively cheaply, and will have by far the largest effect on the RH levels.
- If the humidity is still too high install the transfer grill and fan we discussed in your other thread.
- Air-seal the sill-plate and rim joists with caulking.
- Make a whole house plan to insulate and air-seal, which identifies priorities, and execute that plan over time. This work will have little effect on the interior humidity. It is primarily about energy consumption and comfort.
You can save some money using thinner material on the walls. I like to use a 15 or 20 mil "floor" barrier, and 6 mil on the walls (some codes may require 10 mil minimum now). The walls don't have to take the abuse of people "crawling", so you can go a little thinner there and still be OK. I would run all the way up the walls, often wrapping around the top so that you can tape into a capillary break under the sill plate (if you have one).
I like to use polyiso panels against the walls. You MAY need an ignition barrier when doing that though, check with your local building department. I normally use a fire retardant paint additive mixed in with primer, which satisfies my local requirement for this type of space and application. Some areas may be more stringent. I prefer polyiso panels to spray foam here.
You can often air seal by "foaming in" blocks of rigid foam against the rim joist between the floor joists. This can be more labor intensive, but it's more DIY friendly. I like to use EPS here, but that's not the only option. I use Loctite's TiteFoam to secure the panels in place, which I've found to be more reliable here than GreatStuff. This usually takes care of most of the air sealing and insulating you need, but ideally you want to "wrap around" the remainder of the sill and tie in the vapor barrier on the crawlspace walls. Spray foam makes this easy, but you can also use tape.
You want to check what is on the EXTERIOR of your rim joist. If it's open to the air, just painted, you're fine. If it has something over it that will act as a vapor barrier (like rigid foam), you need to be more careful what you use to insulate the interior. Closed cell spray foam is generally considered to be safe regardless IF you have a capillary break between the top of the foundation and the sill plate / rim joist. I use EPS when I want a little bit of inward drying, because EPS is the most vapor open of the commonly available rigid foams.
I agree completely with Malcolm about looking at air sealing other parts of the house. Air sealing is all about getting the details right, and it's best done as a system that incorporates the entire perimeter of the home.
Bill
Hi Bill,
No sill gasket on my home. What is the benefit of running the barrier up to the sill? Would you still run it that high if using closed cell spray foam? What would you use to mechanically fasten the membrane to support the foam?
Please elaborate on "wrapping around sill" do you mean to spray foam from joist bays down onto the sill and tying into the membrane? How can this be accomplished without spray foam?
When using rigid board on walls, do you put it ontop or behind the vapor barrier? If ontop I would have e to drill through the barrier to secure the board.
The exterior of the rim joist is covered by siding and I presume tyvek or something similar. The siding is suspect and is on the list of things to eventually replace. No evidence of current water intrusion though.
Thanks,
Josh
You want to keep moisture from coming in through the wall too, that's why I include it as something to cover up when encapsulating. I don't like sprayfoaming the walls, but if I did, and used closed cell spray foam, then I wouldn't bother running the poly sheet up the wall. I think it would be difficult to secure the sheet well enough that it could support the spray foam without pulling back from the wall and creating voids, and you don't want any voids there where water could accumulate over time.
I secure the poly sheet with polyurethane sealant as I go, which usually has enough hold to do the job. If I need more hold, I use the little press-in plastic fastners that have a sort of arrowhead matrix that grabs the inside of holes drilled into the foundation wall. I put the polyiso over the poly membrane and secure it with Plastigrip anchors that go through the polyiso, through the poly sheet, and into holes drilled in the foundation wall. This goes quickly and works well. The polyiso helps to hold the poly sheet tightly against the wall. I have not had problems drilling through the entire assembly to do this, although I might reconsider my method if the wall had bulk water problems.
Sounds like your rimjoist can dry to the exterior, which makes it less of an issue which way you insulate the interior side. The biggest thing to remember when insulating the interior is to tie everything together for air sealing. You can do this with spray foam by covering the subfloor, rim joist, sill plate, and top of the poly sheeting. You can also foam in a block of rigid foam over the rim joist, sealing it to the subfloor above, the sill plate below, and the joists on either side, then taping the top of the poly sheet to the sill plate. Either way works. Pick whichever way is the best fit for you and least labor to install.
Bill