Insulating a crawl space: walls and/or ceiling?

thomas1975

11 years ago

I've read through many posts on this but wanted to post with my specific information.

I'm in the northeast
Just moved into the home
Home is 40 years old with a 20 year old addition that created a crawl space that's about 40' x 5 or 6'.
Crawl space is cinderblocks and (knock-on-wood) has so far been very dry.
Crawl space has 3 vents to the outside which are as closed as they can be but let in a lot of cold air.
Between the crawl space and original basement are the 2 original casement windows (which we keep closed) and a full size, well-sealed, door.
The main basement area has a powerful Sante Fe dehumidifier.
Above the crawl space is our kitchen which gets freezing the winter.

I've been told various things by various people (insulation companies, basement companies, contractors...) and wanted to get some opinions here on the following:

1. Should I permanently close off the 3 vents in the crawl space?
2. Should I insulate the walls of the crawl space?
3. Should I insulate the ceiling of the crawl space?

I've been told basically the opposite on all of these questions: yes close the vents they are not necessary, no don't close them as you need the airflow. insulate the walls of the crawl space since if you insulate just the ceiling it will drop the temperature of the crawl space and could freeze my pipes, insulate just the ceiling as that will warm up the kitchen and won't affect the crawl space, etc...

Thanks for your help!

Featured Answer

worthy

5 years ago

last modified: 5 years ago

For a conditioned crawl, the R Value of the insulated walls should be the same as the rest of the home. Silverglo is expanded polystyrene with a claimed R Value of 11 per 2 inch thickness due to mixing graphite into the EPS and adding a reflective coating. This is relatively new in North America. But more than 85% of EPS manufactured in Germany is grey due to graphite infusion. [Incidentally, polyurethane foams are often preferred by green proponents, as they don't contain the toxic fire retardant hexabromocyclododecane (HBDC) that polystyrene does.] A dehumidifier may still be required.

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Comments (7)

worthy
11 years ago
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
poobaloo
11 years ago
Nice article worthy, thanks for that...
I love this part... "DonÃ¢ÂÂt 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...

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

Ã¢ÂÂ¢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.

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

Ã¢ÂÂ¢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.

Ã¢ÂÂ¢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?
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If you can't get into the space and are concerned about moisture, you may want to try what they do with basement walls. You could glue 1" or 1.5" closed cell foam on top of the slab, ensuring all seams are sealed and taped. This blocks moisture coming up through the slab, and cold radiated through the slab. Then go around the perimeter to spray foam any remaining gaps between the slab and the joists, and add molding to seal the space between the slab and the floor joists. The foam board blocks the moisture, and now want to seal the joist areas so that there is no air infiltration. Once you have dead air space around the joists and no cold air entering that cavity, it won't be quite as cozy as having full insulation, but it will be much warmer. Once you stop air infiltration and block the cold radiated up through the slab, your entire joist area will be a 12" thick air barrier. Bruce
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We decided to do exterior rigid foam from top of foundation wall down 2 feet. We will back fill up against about a foot of which will be buried. The other foot will be above grade. We did not take it all the way down because we will insulate the interior wall with rigid foam as well. We covered all of it with propanel that slips under the sill plate so that should prevent any access from the outside via the foam to the sill plate. All siding will then be a foot off the ground and not accessible to the subterranean termites we have in this area. We are still probably going to have the entire property pre-treated as we have already had termites once and do not want to go through that again! What I read about termite shields was not that they prevent access but that they keep the sill plate dry and termites simply don't mess with dry wood. We don't have carpenter ants so I cannot speak to that. I hope what we decided on works for both pest control and preventing drafts.
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worthy
11 years ago
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.
Eddie52
10 years ago
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
John Thomas
5 years ago
last modified: 5 years ago
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.
Rob Frasco
4 years ago
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

Insulating a crawl space: walls and/or ceiling?

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