how to deal with crawl space moisture

[rwhite]

So my daughter's bf just bought a house a few months back and he called me over to look at some mold that was starting to form on an inside exterior wall. I'm thinking it must have always been an issue and is now showing up now that they are living in the house and the heat is on. Anyhow the crawl space is damp. 1st thing I noticed is they had all the exterior vents blocked off. I placed a fan facing down in the crawl space entry and 2 others on one exterior wall blowing in the vents to try and dry it out. Now we need to come up with a long term solution.

1st off the exterior grade is either level or slightly angle toward the crawl space. Actually on the wall where the mold was forming it is higher as they had some type of planter with the dirt mounded up higher than the crawl space. So the question;

Can we come out 2 feet or so from the foundation and dig down 1 foot below the grade of the crawl space and fill with stone or do we need a full blown french drain? There is somewhat of a vapor barrier in the crawl space but it's not properly installed as they didn't bring it up the edges or overlap the seams. I'm thinking that the vapor barrier, stone drain and a few gutters may solve the issue. What do you think?

 

[sportbikerider78]

I'm no drainage expert, but it can't hurt to get water away from the house. If it looks damp....it is damp.

Make sure nothing is near the siding on the outside of the house. Nothing should be touching near the bottom of the siding either. People think it is nice to have shrubs and small vegetation directly up against the house, and they are all wrong. Plants keep moisture.

A simple french drain is really easy to do. Dig a trench about a foot deep and line with that construction fabric. Add some gravel. Place a drilled pvc pipe in. More gravel. Wrap it all up in the fabric. Cover top with more stone. There are many how-to's online and they work amazingly well for being so simple.

Post a pic. Way easier to see whats happening.

 

[Wisneaky]

So my daughter's bf just bought a house a few months back and he called me over to look at some mold that was starting to form on an inside exterior wall. I'm thinking it must have always been an issue and is now showing up now that they are living in the house and the heat is on. Anyhow the crawl space is damp. 1st thing I noticed is they had all the exterior vents blocked off. I placed a fan facing down in the crawl space entry and 2 others on one exterior wall blowing in the vents to try and dry it out. Now we need to come up with a long term solution.

1st off the exterior grade is either level or slightly angle toward the crawl space. Actually on the wall where the mold was forming it is higher as they had some type of planter with the dirt mounded up higher than the crawl space. So the question;

Can we come out 2 feet or so from the foundation and dig down 1 foot below the grade of the crawl space and fill with stone or do we need a full blown french drain? There is somewhat of a vapor barrier in the crawl space but it's not properly installed as they didn't bring it up the edges or overlap the seams. I'm thinking that the vapor barrier, stone drain and a few gutters may solve the issue. What do you think?

I'd do better vapor barrier and also they dehumidifiers that go in crawl spaces.

 

[Highbeam]

So do you have standing water or just moist dirt? Any evidence of flooding in the crawl? What type of soils do you have? Sandy or clay?

Surface water can actually be sent towards your house by poor grading outside, I have seen folks actually have a slope up from the house and then when it rains, the water runs downhill towards the crawlspace and fills it. For no less than 10 feet away from your home, slope the ground at 5% away from the building is the most recent code for my area to solve this. In some cases you may have to build a short wall at 10 feet if the existing slope was uphill from the house.

The next big culprit for crawlspace water is roof downspouts. I have seen these connected to footing drains to actually pump water into the crawl. Not cool. Don't even use splashblocks, actually collect the water and pipe it somewhere else. I sure hope that somewhere on your lot is an area lower that the house.

The final thing that happens is an idiot builder buys a flat lot and digs a hole to build a house. That's fine if you fill the crawlspace back up after the footings and stemwall are built. If you leave a hole then it will fill with groundwater from below. That's no good. The most common solution is a sump pump if you can not daylight a drain pipe from the crawl.

In all cases, a fully intact vapor barrier is required to cover the entire dirt floor. Don't bother fixing the VB until you have your water under control.

 

[jatoxico]

I've fixed moisture issues in 2 houses by doing simple grading and attending to the downspouts. Current house was prone to flooding. The first year we were in the house during spring rains I got frantic call from the missus saying that we had 2" water in the basement. Now I understood the Drylock on the walls and the pump the original owner left us. After removing 12" of soil about 8' from the house I was able to pitch the grade away from foundation and have never had water in the basement again and we've had 2 hurricanes and numerous Nor'Easters.

Amazing to me that this guy lived in the house for 30 yrs with this issue that I solved with a shovel and a rake in a few hours.

 

[rwhite]

No standing water, just damp soil . There was no ventilation at all until I unblocked the vents. The lot is very flat an I'm afraid that if we do a full blown french drain we will have to take the line quite a ways from the house and do a gravel sump. That kind of why I was hoping to just dig about a foot below grade and do gravel fill. It will need to dry for awhile before we fix the vapor barrier. BTW this house was built in the 40's and I couldn't find any indication that this has been a ongoing problem so maybe was just the fact that they plugged all the vents.

 

[DickRussell]

This is good reading, including all 67 comments at the end:
http://www.greenbuildingadvisor.com/blogs/dept/musings/building-unvented-crawl-space

 

[Highbeam]

Without a place to drain your French drain you will have just built a place for water to collect, probably worse than leaving it alone.

Wet dirt is to be expected in flat areas. No problem. Cover it up with a well done VB and cross it off the list of potential reasons for mold. You've probably got a roof leak.