Crawl Spaces and Moisture – lets get them separated

I have been seeing more and more use of a dramatically different but simple solution to the age old
problem of how to best construct a crawl space. Years ago, I decided that they were evil,
but I seem to end up with them in so many buildings that I work on. There are better solutions, especially as we learn how new high performance homes are being constructed.

This week I am faced with proposing a solution to a flooded crawlspace in a 40 year old 2000 sq. foot home a friend wants to rehab.

One problem is the high water table immediately around the house. The backfill soil surrounding the house apparently had a high water retention. And also the rainfall recently has been incredible.

Here is a foot of water in the crawlspace we have to deal with.

Flooded Crawl space

We have to pump it, that’s a fact we cannot change. We need to eject the water a far away as we can get it.

I’d like to always promote best practices, so I prefer the crawlspace be retrofitted with a sump pit and pump, (after its cleaned and remediated, of course).

I’d like a durable, flexible waterproof liner attached to the floor and walls, permanently sealed foundation wall vents, and, if at all possible, insulated walls with 1.5″ thick polyisocyanurate board (just short of R-10 as recommended by the US DOE ). But I am not sure we can do that on foundation walls that have sitting in this much water. The recommendations seem to apply better to new homes more than to retrofit like this. (Folding the vapor barrier into existing joints is not possible, but we can look for alternatives and be creative about that detail.)

In any event, the crawlspace will become a part of the envelope. It will no longer lose heat in winter, with attendant cold floors. It will also act as a heat sink in summer. Some reports are that this type of crawl space reduces home energy consumption by 20-30%. It will no longer be a source of mold spores, rodents, insects, or dirt. To be sure it is vented as required by building code, it should get a small amount of air through small supply and return air grilles, .

ASHRAE has recommended that crawlspaces be treated this way since 1997.

The problem starts with crawl spaces being treated as OUTSIDE the building envelope, But crawlspaces are so intertwined with the structure mounted above them that it seems impossible to reconcile all the conflicting issues without health or durability compromises.

Its ridiculous that most crawlspaces attract and trap so much dirt and water. They are conducive to structural damage as well as contributing to unhealthy conditions inside the home. I won’t list the compromises, but a review of the traditional crawlspace is here article and here
crawlspace info

The International Building Code, which most of Virginia follows, prescribes several rules for crawl spaces as follows

1. Ventilate : Vent sizes are prescribed and are often installed between the outside and the crawlspace
2. Insulate : for generations, floors were not insulated but in the past 30 years, many coes required the floor to insulated. Then the problem of piping was just to insulate and heat trace them or just fix them when they froze. Such reliability!
3. Isolate : Put a low water permeance vapor barrier on the floor to keep the moisture out. Yeah right! It works well in theory only.

Recommendations for constructing a crawlspace in the mixed humid regions ( ranging from roughly from central New Jersey south to north Georgia and west to the central Mississippi Valley.

Sources
US Department of Energy Report:
Habitat Congress Building America: MIXED-HUMID CLIMATE CASE STUDY

ASHRAE Journal Article May 2008,
New Light in Crawlspaces by Joe Lstiburek

http://thecrawlspaceconcept.com/

Tags: Residential Construction