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I have had my home for 15 years in Charlotte. 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 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 which I did explained in the next paragraph. The inspector said that if these actions 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.
Some of the other things that I did at that time a few of which were not recommended by the inspector but by the contractor I used in 2003: 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, and 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.
Check your gutters. If they are clogged or too small and overflowing then it's a good chance this is your problem. Make sure the drains direct water away from the house. Install drain pipe if necessary. Best fix is to replace them with 3x4 gutters instead of the 2x3 gutters that are on most houses.
Bad gutters can cause a lot of moisture to appear in the crawlspace.
Overgrown shrubs & trees overhanging the roof are bad too.
I would focus on surface drainage first. Not just gutters, but yard drainage swales also. I moved into a house with a basement that "flooded". It doesn't "flood" anymore... even with all the rain.
You can't even see my house from the aerial photo on google because of all my overhanging trees, FWIW.
Thanks for the replies so far. Yes surface drainage and gutters can definitely be factors. I do not know what "yard drainage swales" are but I just did some reading to find out; basically drainage ditches.
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.
Ray Terry talks about the crawl space at the 5:20 mark I have listened to the 49:41 minute mark. I'll finish tomorrow.
Went under two homes today at my request. Both were done by a contractor I am considering. The first home has been using the exact same solution that he proposed; a cost effective semi-sealed crawl with dehum for $1,650 at my home. The will replace the vapor barrier, seal all the vents with foam board, and use foam spray on smaller holes/cracks. The wood moisture content was 15% at this first home, down from above 19% during this time of the year, two years ago, before install. Then, he showed me another crawl that was fully encapsulated two years ago. He did not recommend for encapsulation for my crawl b/c he said he didn't think I'd need it, and it was much more expensive; somewhere around $12,000. That crawl had wood moisture of 8% which is about the same as wood when it comes off the kiln.
Yesterday, I got a call back from Advanced Energy in Raleigh, a non-profit, who studies crawl spaces: www.crawlspaces.org
We talked for an hour about my crawl space. The science is their to support sealed vs. ventilated crawl spaces in our humid climate.
I will definitely agree with Ray Terry about the excessive rain being somewhat if not a major contributor to wood moisture content in the crawl in Charlotte.
I will definitely agree about gutters and rainwater management. This is an issue for me in the front of my house and front of the crawl. This is why I extended my downspouts with 10-20 feet of corrugated per downspout.
During Wednesday's 400th downpour of 2013, I went out and observed my roof/gutter performance, and noticed a clot of leaves had "hung" on the very end of the last bit of corrugated pipe of one gutter closest to where I had my highest reading in the crawl. Most of my gutters have covers. This single clot was causing a gutter to overflow and allow water to overflow the gutter and waterfall right to the foundation where some of my higher readings for wood moisture are. But, I know this fix alone will not sufficiently drop my reading there below 20% this time of year.
In many if not most ventilated crawls here in muggy Charlotte during the summer, the absolute moisture content in the air alone, when entering vents and your crawl, then cooling when it enters your crawl (like a cold can of soda being brought outside the fridge); that, and in conjunction with cool air flowing through AC ducts in the crawl; can be alone to keep wood moisture content above 19%.
Sealing the crawl and dehumidifying the air, preferrably with an HVAC guy putting a small vent to the crawl to add some conditioned air, and, provide positive pressure to the crawl space (this is what Advanced Energy told me).
... Lo and behold! At the 39:00 minute mark Ray talks about shutting the vents when a caller about really wet (dripping) wet crawl. Ray is spot on; he agrees with the science behind Advanced Energy!
On comparing sealed vs. ventilated spaces toe to toe; a sealed will keep wood drier than the same crawl space that is ventilated. You
don't have to fully encapsulate your crawl space in order to have it "sealed." Full encapsulation is the most extreme of solutions; but at a premium.
It sounds like callers had good results just from closing their vents. I might go ahead and get the "budget" solution done above, because to foam board insulate all the vents, with foam spray around the edges and all other small foundation openings, and a crawlspace dehum to ensure wood moisture stays low all the time; probably will beat any price on hiring a pro to "perfect" my rainwater in the front. He will probably have to create a swell and/or build another french drain, something that will plug anyway after 10+ years.
I'm not so sure I'd go with this kind of fix. The crawlspace moisture isn't coming from the outside humidity. It's coming from the ground & foundation walls in the enclosed space in the crawlspace. It's made worse here in the Piedmont due to the red clay that holds water for a very long time. Until about 40-45 years ago houses in Charlotte did not commonly have AC and stayed open to the air most of the year without issue. ..except for the ones where water in the yard was a problem.
Case in point, I once lived in a early 60's era of ranch homes in Charlotte. All the homes were built by the same builder using the same standards. No central AC. It was on a hill with a row of homes on one side of the street high up and the others on the other side low that backed up to a creek. The clay ground on the low side was always wet and made worse by mature trees that kept the sun off it. By the 1980s the homes on the low side had mold problems, the high side homes were fine.
If water is pooling around the front, and the clay around your foundation is saturated, then you can bet that it's making it's way into your crawlspace. It's being pulled by gravity and hydraulically even through the blocks and/or bricks that make up your foundation. This is why gutter maintenance is so important here but it sounds like you have a handle on that. It's also why I don't like encapsulation. It's snake oil that eventually makes the problems much worse.
Based on what you have said here, the only real fix is to address the low spot in your front yard. This might mean you have to strip the low spot including removing any trees, lay down some type of drainage ditch filled with stone, then a layer of sand, followed by topsoil & grass.
Barosa, all of your ideas are great. Rainwater and gutter issues must be fully addressed and can be big contributors to crawl space moisture. But to say moisture is not contributed to outside humidity is not supported by science. There is also the issue of cool AC ducts in crawl space, contributing to moisture.
The folks at Advanced Energy at www.crawlspaces.org explain it better than I do, but the attempt at simple: If air outside your home is 90 degrees and is at just say 60% relative humidity, then when that air flows in to your crawl space vents, it is hitting air that is at least 5 - 10 degrees cooler than the air outside the crawl. Because that air coming outside hits cooler air, and cooler air can not hold as much bulk vaporized water as warmer air, then the relative humidity of that air is raised even higher. The cooler air is, the less water vapor it can hold. Its like taking a cold can of soda (representing your crawl space air), then putting outside in the warmth.
The AC ducts create a further problem in the summer. When 60 degree air is flowing through these ducts, it is hitting warmer air in the crawl relative to air in the duct. So, the air just around the duct raises to such a high level of humidity that it turns from the gaseous (vaporized) state to the liquid state. We call it condensation. That's why ducts sweat when AC is running. So the AC ducts can contribute to crawl space moisture. If a duct breaks or falls, it then pours 60 degree relatively dry air in to the crawl, creating even more moisture issues.
Said another, simpler way, here is a short 3 minute video: To Vent or Not to Vent?
It takes a couple minutes to load so be please be patient:
Also note, that "sealed" is not one and the same as "encapsulate." Encapsulation is like a premium form of sealing, that involves insulation wall boarding the inside of the foundation, thicker dirt liner than 6 mil poly, and is very expensive. You can do a "budget" seal by just laying 6 mil poly and foam insulation boarding your vents.
Barosa, all of your ideas are great. Rainwater and gutter issues must be fully addressed and can be big contributors to crawl space moisture. But to say moisture is not contributed to outside humidity is not supported by science. There is also the issue of cool AC ducts in crawl space, contributing to moisture.
Consider this. Clothes hung on a line outside will always get completely dry not matter what the humidity. Flowing air will always attract water from solids saturated with water.
I should have been more clear. When the humidity is high, then water that is seeping into your crawlspace through the walls & soil can't evaporate as fast, and that is why the problem is worsened in the summer. Furthermore when the outside air is hotter than under your house, then air does not flow into the vents unless there is wind. Cold air is heavier than warm. Despite this, some evaporation does happen, even in the summer. If you seal up your vents, then there is no place for the moisture entering your crawl via capillary and gravity action to go except into your wood and up into the house.
Here is an easy test. Try this. If there is an access door to your crawlspace that reaches the ground, then open it for a few days. Night & Day. This will increase air flow dramatically through the crawl especially if there is significant space under the level where the vents are located. (deep crawl spaces) Take your measurements and do a comparison. That will tell you were the problem lies.
(Water condensing off your duct work should not add to the net moisture. Assuming they are insulated then you can do this. Loosely wrap them in plastic then drain & pump the collecting water out of your crawl.)
Last edited by Barфsa; 07-25-2013 at 10:52 AM..
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