Moisture in Crawl Space Puts Structure at Risk, First Aid for the Ailing House uexpress

Moisture in Crawl Space Puts Structure at Risk

by Henri de Marne

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Q: In the fall of 2002, I built a small home (24 feet by 50 feet) on a lakefront property in Swanton, Vermont. There was an existing structure there that we tore down, leaving only the stone fireplace, which was incorporated into the new build!

Footings were poured onto a ledge that was roughly 30 inches below grade. A block wall was then built with four 8-by-16-inch vents for circulation placed roughly 16 inches from the inside corner on a 24-foot wall. Construction was 2-by-10-inch floor joists, 16-inch on-center with 3/4-inch Advantek plywood. Exterior studs were 2 by 6 inches, 16-inch O.C. with a truss roof. The house was intended for seasonal use because the water line from the street is too close to the surface due to the ledge and freezing would occur. Plumbing was done so that all lines could be drained in the fall to prevent freezing of pipes.

In the spring of 2003, the homeowner contacted me and said that when the plumber was in the crawl space pressure testing the supply lines, he noted that the soil was quite wet and felt plastic needed to be spread out over the surface.

They contacted me in the fall of 2003 and said that the plastic has water setting on it and had concerns about moisture. I went and looked at the house and there was water sitting on the plastic. I removed the plastic because of the condensation that was taking place. I then took a small excavator and dug a 20-foot trench from the corner of the house to daylight on the shoreline, but was unable to get 100 percent positive drainage because a vein of ledge protrudes up roughly eight to 10 inches above the bottom of footings. This does drain water in times of significant rainfall.

The following spring the homeowner contacted me again and reported that the soil still seemed to be wet and wondered what else could be done. I contacted my electrician and he installed a direct line fan in the crawl space with a duct line pointing to a foundation vent. This was placed on a timer, which the homeowner has had run for roughly six hours a day for the last 10 years. Vents remain open throughout the year (with the exception of one that is located under the deck and was closed when I checked it on my last visit).

I received a call from the homeowner about a week ago saying that the problem was still persisting and was concerned for the structural integrity of the house. I went and looked at the crawl space and found the following:

1. Significant deterioration of main carrying beam (6-by-6-inch posts are settling into beam due to softness from excessive moisture).

2. Mold is forming on some of the interior joists. This appears to be random with no particular pattern.

Clearly the main carrying beam needs to be addressed for support of the structure, but more importantly, the moisture issue needs to be resolved along with any additional work. I was hoping to get your views on the situation and potential solutions to this problem. Thank you very much for your time, and I look forward to hearing from you. — Vermont, via email

A: It sounds as if water is leaking into the crawl space, since you found some on top of the plastic. Moisture from the soil would not get on top of the plastic unless the crawl space floor is uneven and the seams in the plastic are inverted, with the lower section of plastic below the higher section.

The plastic is essential to contain any moisture and preserve the framing, but it should be installed either in one piece, which should go up the crawl space walls to a point above the outside grade, or care must be taken to make sure that any seam is properly overlapped by at least two feet, and taped.

Any external leakage should also be taken care of with either grading corrections, curtain drain or some sort of effective waterproofing.

I also question the wisdom of keeping vents open since they admit warm, moist air into the crawl space during spring and summer, especially on a waterfront. Vents were — and are probably still — part of some building codes, but they were discredited decades ago when framing was profoundly affected in Southeastern regions of the U.S.

The National Association of Home Builders former Research Foundation (now renamed Home Innovation Research Labs) issued the results of an extensive study on this problem and its recommendations in the 1970s.

Control of the soil moisture and of any external leakage are the best ways to deal with crawl space problems.

Q: When our condo was built, the contractor used asphalt instead of concrete for the garage floor. Age has taken its beauty with oil and paint spots, etc. Is there any cleaner I can use to clean the floor up? — Williston, Vermont, via email

A: Paint can be removed with a semi-solid paint remover. Be sure to check that it is safe to use on asphalt, as some strippers may damage it. Oil stains can be removed by sprinkling hot water on them and sprinkling TSP-PF crystals on the wet spots. Allow to stand for 30 minutes, scrub with a stiff bristle brush and rinse with your garden hose.

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