Damp Crawl Space

[mobile69]

Our house (2yrs old) was built raised about 100cm from the dirt floor, creating a "crawl space" underneath. The outside walls were bricked up & soil added around the outside of the house, creating a bank of earth sloping down to the original ground level. I checked the access hatch today & there was condensation on the underside of the steel cover, & concrete beams damp, earth floor damp. Now, I know that no kind of DPC was used in construction of the house. There are also no ventilation bricks around the crawl space. Until now there are no visible signs of rising damp, but I'm concerned regarding the future. Is this dampness under the house "normal" here, & is there anything I can do to alleviate it? I was thinking of installing an extraction fan in the hatch to change the air under the house. Would only be of use in the dry season, I guess.

[jaiyenyen]

The dampness is not a good thing to have. My advice would be to get some air bricks in those walls.

Regards

jaiyenyen

[Rimmer]

I have a friend who did exactly what you have done, he also had the same problem as you do.

Solution is to put in air blocks on every side to get a free flow of air through the crawl space.

[chownah]

You should check to see if there is standing water in the crawl space during the rainy weather and if there is try to do something to your drainage to eliminate it.

chownah

[mobile69]

Not really practical to put air bricks on all sides, due to covered terraces, walkways. Also, the earth has been built up almost to groundfloor level. This earth slopes gradually away for about a metre or two, then fairly steeply to garden level. The garden is pretty well drained, sloping away on all sides. Runoff from the roof flows away from the house. I suspect the moisture is coming thru the bare soil under the house.

I've been doing some research on the www, & opinion seems to be away from vented crawl spaces, especially in humid locations, and towards sealing the crawl space with plastic sheeting, including the side walls & posts. The problem being if the vents draw warm humid air into the crawl space, where the air is cooler, the relative humidity increases, bringing about condensation.

[tjo o tjim]

You really are best off venting the crawl space if at all possible; it is required by code in the US for a few different reasons, some of which don't apply in Thailand (mold, which is unavoidable here, and radon gas, which I don't think is a problem here).

If you can make a perfect seal, it isn't a problem; just a vapor barrier on the ground will help somewhat. Another option is to run a PVC pipe from above ground into the crawl space on two sides to at least allow for some potential air movement. (Stick a small fan on one of the pipes if you want to force air through the space.) The tendency is always for mass diffusion, so the dewpoint of the air should be consistent in the crawl space and outside.

You are not likely to ever have a lower dewpoint in the crawlspace relative to outside without a perfect vapor barrier and dessicant, so the advice you cite seems odd to me.