cawl space insulation

[Cheers]

I have an unheated crawlspace under our living area . It is made with cinder blocks and above grade . I plan to insulate the outside with foam insulation. How thick should I go? I was planning to go 3 inches

[jentz]

House above grade?Insulate the floor.You want circulation under the structure to prevent moisture buildup.Creating a barrior traps moisture.IN A PREFECT WORLD oops caps! some blocks should be missing they should be screened to let air flow.

[Cheers]

Sorry I guess technically it is heated . I dont have heater in crawlspace but it is warm from the heat escaping from the living area . I do have plumbing in the crawl space so it cant be allowed to freeze

[reddog]

Condition it as you would if it was part of your house. Heat it, cool it, mechanically ventilate it. Bad things happen in a heating climate when you try to disconnect your crawl space from living space. To answer your question, 3inches should suffice. Do you currently have a ground cover/vapor barrier over the dirt floor,.(assuming you have a dirt floor) is 3inch foam readily available in your area?

[Cheers]

I plan on doing a plastic on the ground . As for the foam I can get up to 2 inch sheets. My plan was to put layers on and over lap the joints . I screwed treated 2x4s horizontally along the wall and put 1.5 inch thick sheets in between then another sheet over top screwed into the 2x4s with screws and fender washers . I saw Menards has 1 inch sheets that have stuco on them, I was thinking of putting them over top and finishing the top with a flashing/drip cap and calling it done .

[reddog]

Sounds like you have a plan that will work. Use the heaviest mil vapor retarder you can find.(minimum of 6 mil). Seal the joints together, and tape seal it to your foam insulation, or sandwich a 30inch strip between the foam and tie onto it with the floor sheet when you're done with the work your doing in the crawl. Don't forget about foaming the rim joist area also. If there's already batt insulation in the rim joist, remove it and replace with rips of foam. Batt insulation is not good in the rim joist in a heating climate, and even more so in a dirt floored crawlspace

[Tom7227]

Sounds like you have a plan that will work. Use the heaviest mil vapor retarder you can find.(minimum of 6 mil). Seal the joints together, and tape seal it to your foam insulation, or sandwich a 30inch strip between the foam and tie onto it with the floor sheet when you're done with the work your doing in the crawl. Don't forget about foaming the rim joist area also. If there's already batt insulation in the rim joist, remove it and replace with rips of foam. Batt insulation is not good in the rim joist in a heating climate, and even more so in a dirt floored crawlspace

Another reason to 'overdo' the plastic one the ground as is suggested here is to limit the radon. I had a test done and the result was high. A contractor talked about sealing up the crawl space area the way described. If you're going to do it doing it correctly isn't that much more work.

[givetoget]

Reddog I have bat insulation in my rim joists. I guess my ? is why is that bad. Should I pull it all out and put foam in there instead.

[corncob]

Too many voids with batt insulation, especially along rim joist, corners, sills, etc. Sealing all edges, seams, gaps, cracks, is critical in order to prevent air leaks....Insulation is very much compromised if any air flow or leaks are not addressed.

[givetoget]

AH Yes CC I doe see your points. Hey thanks ya just gave me another winter project. LOL

[reddog]

Its not so much the fit and finish of batt insulation but more the fact that there is no vapor retarder in place in a rim joist application. This doesnt matter if its a crawlspace or a basement,although a crawl typically has more moisture exposure than a conditioned basement. Water does not like being in a vapor state and is constantly searching for a cool surface to condense on. A rim joist is a perfect spot for water vapor to migrate through the batt insulation and condense on the rim joist in the winter. When the rim joist gets cold enough, the.moisture turns to frost and the larger the temperature differential there is between inside and outside the more moisture accumulates on the rim joist. Thats why rigid is so much better.

Now, back to deer hunting