Thread: CRAWL SPACE: interior drain, encapsulate, or ...???

I have had my home for 15 years. I don't ignore my crawl space. We have had a lot of rain this year in Charlotte, so, I am fighting a bit higher moisture readings in my wood, 19% to 25%, most typically in the front part of my crawl space where the soil gradually slopes down to the home. I pulled my inspection report from 15 years ago before closing the sale. The inspector then said I had moisture readings of "15% to 22% ... some mold and mildew.... no action recommended at this time."

In 2003, when I had a broken AC duct in the crawl pumping cool air and condensate in the crawl, I had another crawl space inspection only done. This was also the last really wet summer. The inspector at that time found wood moisture at 14%-25%, with soil damp or wet under the vapor barrier. The lower readings tended to be nearer the existing forced air ventilator which he praised. He recommended adding more vents, and, a few other things, and if that didn't bring down wood moisture level readings, install a French drain, preferrably on the interior of the crawl space. I also had the AC duct repaired. Again, this was 2003 - last really wet summer.

I've done some things in the past: added another fan in the sub floor on the other side opposite from the existing force air ventilator fan, added a sump pit and pump, added even more vents and vent wells, but the problem during the 4 humid summer months does not go away; a bit too much moisture. But I've been given different ideas:

1. full encapsulation

2. interior drain around the front inside part of the crawl

3. combination of 1 and 2

4. new vapor barrier to replace the existing barrier, seal the crawl space vents, but don't fully encapsulate and add a crawl space dehumidifier -> this guy said I don't have standing bulk water in my crawl space, that the humidity level is high in the crawl contributing to elevated wood moisture readings during this wet summer.

The two subfloor fans I have are both hooked to humidistats set to 70%. Both run almost all of the time in most of May, June, July, August, and early September. They almost never run during the other 8 months.

Any thoughts?

Thanks

If I understand correctly you have exterior wall vents that permit outside moisture laden air into a cool crawlspace. Introduction of hot humid air into a cool crawlspace will permit the humid air to condensate (dew point). Thus anything such as wood will result in higher moisture readings.

I would suggest temporarily closing off any exterior crawlspace vents and installing a dehumidifier and run for a week and see what results.

Solving crawl space humidity and moisture problems with science read all about it

Thanks for the tips, please keep them coming.

Yes, in response to Raymond Wand, I have been studying the debate of ventilated vs. sealed crawlspaces in the humid south. Yes, not only do I have open crawl vents, I had more added back in 2003, the last time I "addressed" crawl space moisture during the last big rainy year in Charlotte.

I have studied Advanced Energy's www.crawlspaces.org website which supports sealing the crawl.

One of the now 4 or 5 folks I have had out, suggested that very same thing that Raymond suggested; sealing the vents and using a dehumidifier. His pest control company will seal all of my foundation vents and any pipe openings to the foundation. They will lay new 6 mil vapor barrier, and add a dehumidifier all for $1,650 for a 2600 sq. ft. crawl. They will not put insulation board on the inside of the brick foundation (brick skirt). His belief was that standing/bulk water inside my crawl is not the issue, rather high humidity (vaporized moisture) is; some of that a result of AC duct condensate.

Another pro that came out working for a reputable local waterproofing company hasn't gotten me a quote yet, but said that encapsulation and putting an interior drain on the inside of the front foundation crawl; the front and side of foundation that receive the gentle downsloping soil, will be what he recommends. He said the interior drain is a first step, but he doesn't think that will completely solve the problem of elevated wood moisture content during rainy, wet, humid summer months which is why it sounds like he also recommends sealing.

One other thing about rain water:

One thing that I did not mention in 2003 was work done, both in 98 and 03 on the gutters. In 98, many sections of my roof had no gutter at all! The rain would just run off in the roof and drop right by the foundation! So, I had guttering and commercial size down spouts added to every edge of the roof.

Then, in 2003, as part of the last big attack against moisture in the crawl space, the contractor I hired to do work in the crawl, also mentioned roof rain runoff. Even though in 98 I had guttered everything, the downspouts mostly were just coming straight down and putting rain almost right by the foundation, except for a small splash block which isn't much.

In fact, the front of the house, like I had said previously, where the wood moisture content can be the highest, right in the middle of the front is a concrete approach to the front door. During heavy rains, down spouts on either side of this concrete approach would cause a ton of water to collect on this concrete. We are talking about an inch or two of standing water!

So in 2003, I added corrugated piping to the end of the downspouts. Some sections are as long as 20 feet, to attempt to get rainwater away from the foundation and to a low spot.

For the two downspouts right by the front door and concrete approach, I dug two trenches, and laid about 10 feet of corrugated piping for each downspout with the end being slightly lower than the beginning. These two helped tremendously with water collecting on the concrete approach to the front door; it never does. But, because the overall slope of my front yard is a slight down grade from the street level to the front of the house, I can't say that my corrugated piping extensions keep all of the water away from the foundation. And with the ton of rain we have had the first 6 months of this year, my corrugated pipe extensions and the soil it feeds can handle an occasional downpour, but downpours every other day have kept the soil wet, if not soaked, so often the ends of these downspout extensions pool up with water.

The other issue is all of the impervious area right in the front of the house; the concrete approach to the front door, and very large asphalt circular driveway will make it difficult if not impossible to add swales/ditches to the front of the house to encourage almost all of the rainwater to a low spot to the side of the house and away from the foundation.

Thanks for any tips. Keep them coming.

Todd,

Building Science Insights

BSI-009: New Light In Crawlspaces

By Joseph Lstiburek
Created: 2008/10/16Also - BSI-009: New Light In Crawlspaces ? Building Science Information

Originally Posted by Raymond Wand

Todd,

Building Science Insights

BSI-009: New Light In Crawlspaces

By Joseph Lstiburek
Created: 2008/10/16Also - BSI-009: New Light In Crawlspaces ? Building Science Information

Thanks Raymond. Yeah I've been here before as well. Not quite as easy as Advanced Energy's website to pick your way through, although on the Building Science Insights website you can at least do a search on "crawl space" and get some things.

Todd,

Have you considered making the CS a conditioned space, by knocking out a section of the foundation which adjoins the CS creating an opening. Then running a supply duct from your furnace so that the conditioned air can circulate with the interior environ?

DOE Building Foundations Section 1-1

"most typically in the front part of my crawl space where the soil gradually slopes down to the home."

I would start looking at the grading and downspouts around the house first. If you have a yard with a slope towards the foundation, where do you think that runoff and drain water goes? Cutting a swale across the yard and redirecting water drainage would be a good starting point. How about grading around the house? Settled backfill at the foundation traps water. Downspouts draining onto grade at the corners of the house? Add a vent blower to keep air moving in the crawl space while fixing the drainage around the house.

I'm not a big fan of French drains inside the foundation walls. It just makes more sense to me to capture excess water before it gets under the foundation.

Originally Posted by Stuart Brooks

"most typically in the front part of my crawl space where the soil gradually slopes down to the home."

I would start looking at the grading and downspouts around the house first. If you have a yard with a slope towards the foundation, where do you think that runoff and drain water goes? Cutting a swale across the yard and redirecting water drainage would be a good starting point. How about grading around the house? Settled backfill at the foundation traps water. Downspouts draining onto grade at the corners of the house? Add a vent blower to keep air moving in the crawl space while fixing the drainage around the house.

I'm not a big fan of French drains inside the foundation walls. It just makes more sense to me to capture excess water before it gets under the foundation.

Yep, working on the downspouts, got those extended using corrugated pipe for the front downspouts, then I am going to get those tied in to some sort of trench drain away from and in front of the front foundation, which will capture most rainwater and move it to the left of the house where a strategic low spot is.