Crawlspace treatment in Midwest

[dmwyatt]

I'm about to begin a spec home on a crawlspace. Crawlspace construction is a first for me, 99% of my homes are on a basement with a couple homes on slabs.

Looking for advice on how to treat the area when it comes to insulation and ventilation. Bulk water shouldn't be a problem. Location is about an hour drive South of St. Louis.

Normally I'd consult with the inspector on this, but this house is out of any city limits, and our county has NO building inspections! (Rural county with a population in the mid 40 thousands)

My gut instinct is to just fill the "floor" with 1-inch clean gravel that can drain to daylight just in case, and insulate the rim joists with fiberglass insulation with no ventilation. Exterior wall WRB come down over mudsill...

Advice?

[Toolwhore]

dmwyatt;

Even with the best drainage, the soil under crawl spaces always carries some ground moisture, which will tend to migrate up to the crawl space in the form of vapor. This vapor can be controlled with a barrier laid directly on the ground. In vented, unheated crawl spaces, the circulation of air through vents will remove any excess moisture. Crawl space barriers should be 6 mil.(min.) black polyethylene. In some regions, ventilation is also required to remove radon gas. (don't know if that applies to your area, but if it does, seeing as there is no inspection, it might be a selling point in a spec) The net area of venting is related to the under-floor area and to the climatic and groundwater conditions. Net vent area should equal 1/150 of the under-floor area with a reduction to 1/1500 if a vapor barrier covers the ground. Vents should supply cross-ventilation to all areas of the crawl space. Locating vents near corners and on opposite sides of the crawl space is most effective.
That said; Some people believe that foundation vents can be eliminated altogether when accompanied by the complete sealing of the crawl space floor and foundation walls. ( I have never used this method, the former has always worked out just fine for me)

[BillHartmann]

In his location the the humidity levels during the summer is HIGH. Dewpoints often get into the 70's.

You DO NOT WANT TO ALLOW THAT OUTSIDE AIR INTO THE CRAWLSPACE.

Go to www.buildingscience.com and look for houses in the mixed humid category.

BTW, IMNSHO, MO is not in the midwest. The term widwest was orginally used with OH and In where first being settled.

Generally MO is a plains state.

But where he is I would call it Southern.

Look at the map is near TN.

[dmwyatt]

Originally Posted by BillHartmann

BTW, IMNSHO, MO is not in the midwest. The term widwest was orginally used with OH and In where first being settled.

I don't know anyone who actually lives here that wouldn't consider us as being midwestern.

Other sources tend to support the thought.

Regardless, it's all semantics.

Thanks for the advice fellas.

[phillip]

we always make a crawl space like split foyer foudation
gravel
sump bucket
radon vent
plastic
concrete slab
insulate the walls with rigid foam
no out side vents

[Firehammer]

In KC we consider ourselves from the Midwest... Totally and completely. We always question why Ohio is considered midwest. Guess it's just how you were raised.

[Wes]

I just finished a house in NW Oklahoma that has a sealed crawlspace like you are talking about. after the block was laid for the stem walls we sealed the block with tar, 2 inch foam on inside of wall, then laid 6mil black plastic in one large piece(40x100) in the hole. After cutting and sealing around the piers for the floor beam we put our top plate down over the plastic, the plastic was later pulled up the outside walls and the housewrap over lapped the plastic.

After the house is up the most important part is to make sure the HVAC crew has a return vent and several supply vents installed under the floor(the ratio is in the 2003 ICC code book). I used to really be a slab-type guy but now see a lot of advantages to the sealed crawlspace in many parts of the country.