Water and moisture in the crawl space 3

[aey53]

I have a question concerning Crawlspace ventilation and drainage. The problem is I have recently purchased a home, which has poured concrete crawl space walls and a dirt crawl space floor and no vapor barrier. Since it is spring and rain seems to be a weekly event, I have noticed a small amount of water on one side of the crawl space (about 1-2 inches deep in the low lying areas) and the rest of the crawl space’s dirt is moist. This past winter the ground and walls were also moist. I live pretty close to the top of the hill except obviously not all the way at the top. This side where the house slightly protrudes into the side of the hill is where I am seeing this water in the crawl. The house is about 6 –7 years old, and I don’t think there is footing drainage system (perforated drain pipe at the base of the footing). The outside ground level is about 15-20 “ below the crawlspace floor level.
I would like to hear everyone’s thoughts on what should be done. The downspouts on the gutters have 10’ sections of ADS pipe routing the water away from the house. I plan on installing a permanent drain system for the gutters using 4” PVC and I also considered installing the perforated pipe at the base of the footing at this point also. I was also considering installing a crawlspace fan since I don’t have enough vents; there are only 4 for this 1800 sq ft. home, because of the wrap around concrete porch. Can anyone help direct me in the right direction?

 

[CESSNA1]

ADYOUNG: Here are some suggestions. Check the water runoff during a strom and make sure it flows around your house, not not it. There may also be an underground water table close to the surface and it rises slightly in a rain. I would suggest that at some point you install a moisture barrier on the soil under the house and you may want to consider installing gravity drains/sump pump in the crawl space. If the water is coming from below you will need to fix that before installing a vapor barrier.

Regsrds
Dave

 

[oldestguy]

Here goes with some preaching.

Any sub-drain you use is best placed to cut off the flow of water towards the area you intend to protect. That is like making a moat around a castle. Drawdown drains are rather ineffective for any lateral distance.

Get the drain deep enough to do that cut off.

If you are in northern areas where freezing is a problem in winter, where you dump the water is important, since a frozen outlet will stop up the whole system. You may have to pump it out on the ground from a sump inside the crawl space.

Then, here is the most important point of all. Do not use any gravel as backfill. Gravel is not a filter and it easily plugs up, and in some cases, allows erosion of soil via its void system.

The best backfll material is the fine aggregate that is used in concrete, ASTM C-33 sand. In our area they call it "torpedo sand". Seal the top of the sand (ditch) with clay. No point in draining surface water with this subdrain.

If you use a sock on the slotted pipe, that may be what some feel is enough, but these have been known to plug up with mud over the slots underneath. Skip the sock and use the concrete sand directly against the pipe. A small amount of finer grains will get in, but no big deal.

On my jobs I specify "NO GRAVEL ALLOWED ON THE JOB", since some well meaning worker will use it instead of the sand.

Of all the underdrain jobs I have supervised, not a one has failed in over 45 years use in some cases. Use gravel and many a job has plugged up.

You may have some dummy building inspector wanting to see gravel, but don't do it.

As a different approach, take a look at the outside backfill to the building. Was it shoved in against the wall, with layers sloping towards the wall? Once in the soil, the water will follow those weak lines towards the house. This happens even if the surface is properly sloped.

In some cases, no drains are required if you waterprof the ground surface to keep out the surface water. Of course if it is ground water thing then this alone will not solve it.

Waterproofing method:

Strip the sod. Roto-till in about 2 pounds per square foot of Volclay (drillers mud) (a powdered bentonite). Do not use granulated bentonite, since it won't mix well. Work this in at least 2 prefereably 3 or more inches.

Use too much bentonite and you have a greasy mess. Don't exceed 3 pounds per s.f.

Put the sod back on and grass will grow very well there due to the attraction of water to the bentonite, filling the soil voids

Where you can put a decent slope to that final surface away from the house, fine, but be sure to cover all of the backfill (maybe as much as 10 feet out from the wall).

Don't depend on plastic sheeting under stone or bark decorative areas. It leaks real bad in time. Also, these decorative areas usually are "undrained bath tubs". Take extra care to be sure of a good seal. Work closely around shrubs.

Joints in concrete slabs also leak. Use the soil-bentonite mix there as a seal.

As a final thought, is the dampness causing mold or other problem? If not, maybe live with it. I once lived in an old house with a spring under it and we survived.
Good luck.

 

[bimr]

Some good comments by the previous posters.

Do not under any circumstances install a crawl space fan or vents. Typically the crawl space is cooler (from earth contact) than the outside atmosphere. If you install vents, the outside air will enter the crawl space, then cool and condense in the crawl space, adding moisture to the crawl space.

Instead of a vent, consider adding a dehumidifier.

As a minimum, cover the ground with plastic. Consider adding a sump pump at the low point. If you do not, the water will cause corrosion.

An outside foundation drain is the preferred cure, but will be expensive.