Most of the floor of the crawl space under my home is dirt floor. What, if anything, should be done to a dirt floor crawl space to better insulate/protect my house?
The best way to insulate it would be to lay down a good 4-6 inches of gravel over the dirt and either mechanically fasten or adhesively fasten some type 1 polystyrene to the underside of the floor joists. That should save you some money on heating costs.
I assume that the floor over the crawl space is insulated. Are you having problems with drafts or is it a cold floor? If that is the case, if room allows it I would make sure you install 6 mil plastic over the dirt, this will stop any moisture from causing problems with the insulation. Also make sure you have air circulation under the house, this will keep every thing dry.
Ideally we would recommend that you you insulate the portion of the perimeter concrete walls that is above grade using rigid extruded insulation, permanently close off any existing through wall ventilation, lay down a plastic vapour barrier over the dirt floor, install a 2" skim coat of concrete over the plastic, and ensure that there is at least one heat supply and return air vent opened to the crawlspace (in the case of forced warm air heating).
Heating the crawlspace will remove the requirement for ventilation while at the same time providing a nice warm floor above.
We encapsulate crawl spaces with the use of 12-20 mm reinforced vapor barrier and butyl seal tape (Designed specifically for crawl spaces). The top side is brilliant white therefore enhancing the lighting if used as a storage area. The reinforcement allows for extra strength to eliminate tearing. The whole idea is to close off the venting if it is an open vent system.
Next we deal with what is referred to as PERM (a term used to describe a certain amount of water vapor that migrates through a product over a specific area over a specific time period for a specific pressure).
I could go on for a bit but The idea is to stabalize Relative Humidity and temperature through the use of products that will eliminate the PERM as much as possible.
I agree with the former writer that suggests the use of rigid foam on the perimeter and then applying a vapor barrier, of course one that I use and recommend that is specifically used for this application. It is available in both a regular and antimicrobial with a PERM level of 0.0185 Grains/Hr/Sfin.Hg.
Some crawls may also require a demumidifier and possible drainage systems and sump pumps depending on the severity of moisture issues.
Crawl spaces are dealt with in one of two ways, insulated or not insulated. Not insulated there are vents/openings all around the foundation wall to allow for air flow, so no moisture builds up.
In this case the house is insulated and vapour barriered underneath the floor joists only. The other way is to treat the crawl space like a full basement. The walls and floor are insulated and vapour barriered, and the outside vents are closed off.
Now there are numerous ways and opinions on how to insulate a crawl space. One of the best ways is to lay down a vapour barrier, styrofoam insulation and then pour concrete over top. The floor is now insulated, dry, maintenance free and can actually be used for storage if you wish. The exterior walls will also need to be insulated.
If what you call dirt is gravel. I would insulate with an SM type product covered with 6 mil poly or delta wrap, foundation waterproofing. This will remove quite a bit of moisture in the air.
I have included 2 photos of my own place before and after.
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