In regions with extended periods of humid hot conditions, such as the northeast US, closed insulated unvented crawlspaces work best in keeping out mould-inducing humidity from the crawlspace and the living space above.

So air seal and insulate the walls of your crawlspace but ONLY with foamboard or sprayfoam.

Here is a link that might be useful: The Scary Crawlspace

Nice article worthy, thanks for that...
I love this part... "DonâÂÂt vent dryers or other appliances into the crawl" Who would do that? Every load of washing machine water direct into your crawlspace. Sheesh.

For closed conditioned crawl spaces the recommendations were...

â¢Insulate the perimeter walls to the level suggested for above-grade walls in your climate.

â¢Exterior perimeter wall insulation is a good option to consider, especially in new construction. It eliminates the problems of moisture management associated with interior wall insulation and provides the possible benefits of additional thermal mass within the structure. The downside is you have to protect the insulation from termites and the above- grade portion of the insulation from deterioration caused by weather exposure.

â¢When insulating a crawl from the interior, you should protect rim joists from condensation with foam insulation.

â¢Use water-resistant insulating materials, such as rigid-foam board or spray foam properly protected to meet fire ratings. Avoid using air-permeable insulation, such as fiberglass batts or spray-on cellulose.

â¢Power venting a sealed crawl space to the exterior can reduce the movement of air from the crawl space into the house. This can improve IAQ, but at the added cost of operating and maintaining the exhaust fan.

I just might do that. i.e. insulate the walls and rim joists cuz our floors over the crawl space zone of the house are really cold in the winter. The issue there is "properly protected". Per the fire ratings, XPS sheets are to be covered w drywall or finished. Obviously a crawlspace you're not going to finish in drywall like you would a full height basement. So they don't really address what to do there -- cant leave it exposed but you're not gonna frame and finish...
Thoughts?

If the crawlspace is only used to access utilities, an ignition barrier--as opposed to a thermal barrier--may be used, which may be somewhat less costly to install. Intumescent coatings can be used. Thermax, a polyisocyanurate sheathing with a metal foil covering, is often used in commercial settings.

Get the approval of the local building authority to be sure. In case of damage claims, insurance companies may use non-code compliant installations to deny coverage.

I live in the capitol of hot and humid and closing off the foundation during hot and humid is not what we do here as the air stagnats and it rains under the house. We generally use the simple vents that close themselves when temperature gets below 50 degrees they are a stock item at the home depots around here.

I made the mistake of closing in one of my original homes I built here with an insulated foundation with closed foundation flood vents and failed to put a vapor barrier on the soil i.e. visquinn so it turned into a sauna after awhile.

Try covering the earth with visquin first its inexpensive and may solve your problem.

Good luck,

Eddie

Opening up an old thread here as I still haven't made a decision as to what to do...

I just had an insulation company come out and they suggested installing a 20 mil vapor barrier along the floor and going up a few feet on the walls, and then spraying the walls with 3" of spray foam. Price of $1,500.

I also had one of the big Connecticut basement system companies come out, and while I thought they would be ridiculously expensive and would try to sell me drainage, etc... they weren't, and didn't. Price was actually less than the guy above, but rather than use spray foam they have their own system consisting of various layers of 'stuff' (CleanSpace, drainage matting, terrablock, silverglo insulation board...). Price of $1,200.

Any thoughts on these 2 proposals? I really thought the big CT basement company was going to be much more expensive, and say that i needed drains or whatnot installed, but they didn't. They said the space looked pretty good and would be an easy fix...

As an aside, I also found an old estimate for another company several years ago for $1,500, but it was only 2" foam and no vapor barrier, so the $1,500 above is of course a better deal.

I'm mainly concerned that after I do all this I'll still to put a big dehumidifier in the space, unless the vapor barrier and insulation itself keeps it out.

John Thomas what did you wind up doing? Was in a similar predicament and it’s astonishing how different the proposals from companies are that are all doing the same type of work