Insulated Crawl Space [Archive]

Anonymous

September 12th, 2002, 07:13 AM

Posted by: Wgoodrich
Posted - 02/16/2002 : 10:54:51

Common building practice in our area is to do as you are thinking. In my opinion creating a warm crawl is a better choice. Too many times I have been in crawl spaces that have insulated the floor only to find the insulation to have drawn moisture and now is a mess in the crawl having drawn moisture, gotten heavy, and ripped down from the crawl not insulating that floor anymore but making a big mess. I think you have a sound idea.

There are a one different idea that I am not convinced worth doing. Some use blue board to insulate the earth from the crawl. This idea I am not convinced to be a good idea. It is a fine idea when insulating a basement floor but not a crawl floor without a concrete flooring.

Most common practice is to ensure you have the required vents in the walls of the foundation. This provides an air flow in the crawl space during the spring, summer, and fall when the ground's water level is normally high. Make sure you install the type crawl space vents that have a slide on them so that in the fall in preparation for winter months you can make a trip around the outside of the home and slide the louvres shut for winter months. This creates a sealed crawl space creating a dead air space. This efficiently prohibits freezing of pipes etc. as long as you have properly built the footing and foundation void of air leaks. The temperature of the earth should be about 55 degrees. Heat rises therefore the heat of the earth will heat your crawl space in the winter buy the heat rising in the trapped air void. Next problem is moisture in the crawl that is a preparation problem that you must address before string out you house to dig the foundation.

The CABO Code book requires that you remove the sod from the crawl space area, before you start building. The CABI Code also requires you to build your home on a solid foot. That means no fill. A lot of people think this to mean that you can not add fill in your crawl space. This is not true. The footing must not be on loose fill, this is the footprint of your home. The crawl space if just an air void area within the footing. When you pick you location to build you home. You should do some research. Have a surveyor or experienced excavator to draw a minor topographical map of you land where you plan to build your home. Make absolutely sure that you are not building in the low area of that surrounding land, and whether you are in a flood way or flood way fringe area. The CABO Code requires the first floor of you living area to be a minimum of 2' above flood level in you topographical area. This will prevent you happily moving into your home and in the spring be leaving your home in an emergency flood escape by boat. Make sure you are not in an area that is flood prone. Then try and confirm the normal water level you your area even if you are not in a flood area. Water level in the spring can be as high as the top of the ground. This is the underground saturation level the water gets during the spring rains. Confirm that you have your crawl space floor above normal water level. If you can try and make your crawl space floor even with the normal plane of you surrounding land area and hopefully the elevation [height] of the road. This will mean that instead of doing a push out you will be hauling in a bit of dirt as fill around you home for your yard area. Once you have the location of your home picked and the elevation of your crawl ensured that it will be above high water level in the spring then you need to string out you home and dig the footing. The footing must be dug to a point below freeze level in your area. In midwest that is about 30" deep minimum. It is ok to go deeper and add an extra row of cement blocks in your foundation to bring your house up to a minimum of 2' above high water table during spring. Once you have dug your footing then stake out the elevation of the top of your footing for your concrete pour of wood footing. At this time make sure all sod has been removed from the crawl. Just the sod no dirt. Then use pit run or other type of fill to fill the inside area of your footing while you are installing your foundation. Make sure the floor of the crawl is a minimum of 6" above it surrounding yard area finished grade. Once you have the floor of the crawl 6" above the surrounding finished grade of your yard then take bisquine that comes in rolls large sheet type. You can buy this plastic sheeting wide enough to reach the entire width of your home. If you can't find this plastic bisquine that wide then buy the rolls as wide as you can and overlap the runs of plastic by 12" side to side to ensure a moisture seal. Lay this bisquine like a blanket over the entire floor of you crawl area. Then bring in pea gravel so that you have about a 6" thick layer of pea gravel spread over the bisquine. This creates a moisture seal that will allow the heat to rise from the earth into the crawl during the winter months but seal out any moisture.

In the spring open you foundation vents and in the fall close you foundation vents. This is all the maintenence you will have to do. Just walk around the home and slide the foundation vents open and closed during those two season.

Once you have layed you plastic blanket and pea gravel over that blanket and have built your foundation to the point so your first finished living area floor is 2' above high water ground saturation, and have installed you anchor bolts in the foundation to bolt the wood sill plate to the foundation then build your sill plate on the top of the footing. At this time then install what is called syrofoam blue board to the crawl space wall. This blue board is pretty thick and pretty stiff. It also comes in widths to match your foundation height. You can spread a tacking glue to the foundation wall but often times this is not necessary. The blue board should squeeze between the earth in the crawl and the sill plate and the bottom of your floor joists. Make sure to cut out for you foundation vents in the blue board This makes a thermal seal and still allows venting of air in the spring, summer and fall. Then once you have installed your floor joists and your sub floor then crawl into your crawl and take vapor paper backed style insulation and stuff this insulation between each floor joist above the sill plate and below the sub floor, shoving this insulation in the square area discribed making a seal of heat and moisture in this area. Now you have a heated crawl space that will serve you comfort and a reliable crawl space to promote long life of you home without concern of rotting your wood due to too much moisture. Remember also that your heat ducts should be the insulated heat duct design to ensure effeciency of your heating system. There will be some heat loss that will help heat the crawl space even if you use insulated heat ducts so don't concern yourself with heating the crawl with your heating system. This crawl will stay above freezing if no heat ducts are even there. The heating system is not supposed to or needed to heat the crawl space area.

Hope this helps

Wg