condensation under the house

[badgolferman]

It seems there is condensation building up underneath my house on the end near the garage that doesn't have foundation vents. Some of the joists have mold or a fungus on them. The prior owner installed some crawlspace fans and had them on a timer. I went under there today and moved one of the fans from under the porch to that wet area and aimed it toward the other fan that was blowing in the direction of the vents at the other side of the house. I had to run a new wire from the old location to the new location of course. I've left the fans on continuously and will check it in a few days.

The exterminating/moisture inspection company that told me about the problem has offered a $560 treatment that sprays all exposed wood under the house and kills any thing that is alive now. I've considered going under there and spraying bleach/water solution, but I don't think I'll come out alive.

Does anyone have experience with this?

[buffalobill]

your climate and precipitation will provide a better answer to you if you ask your good neighbors how they handle this. otherwise get a garden hose attachment or a gallon pump up sprayer and lots of bleach, figure on diluting to 3 percent bleach. if you have high humidity at night perhaps run the fans if humidity is lower in the daytime. if you want to dive into the research, there's a world of knowledge for your home depending on what climate you live in. free, at:

[RogerT]

It would probably help to know where your home is located to get a better idea of the climate in your area. Also, is there any insulation between the joists (with or without facing)? And, is it an uncovered dirt floor in the crawl space, or some other type of floor?

I recently went to a meeting where an inspector talked about this condition. He suggested no insulation between the joists or, if there is insulation, to make sure it is unfaced insulation. He said placing 4-6 mil plastic on the dirt floor can create a moisture barrier to help prevent the moisture in the soil from coming up. And he said that sometimes no vents are better than having vents because the warm humid air from outside can come in through the vents and cause the condensation you are seeing -- especially if there are fans operating which bring in the humid air.

[aemeijers]

Back in stone age when I grew up, crawlspace vents were SOP, and visqueen was still an exotic product. There was some accepted practice for when to open and close them, but since the handles were on the inside, nobody ever did. Fuel was so cheap, nobody cared. I still remember being in single digits, being drafted to ferry insulation across crawlspace and attic, where grownups fastened it into place, and seeing the stripes and bare spots on roofs when heavy frost or snow came along. Haven't seen crawl vents on new construction in decades. Not that crawls are common here in basement country, other than on modular and starter houses, but insulated foundation walls and double-plastic dirt cover are the current practice, which almost brings the crawl inside the heated envelope, since a deep crawl will never freeze hard due to ground heat and house leakage.

When I hit the lotto and build my dream house, I'll pick location carefully so water table won't be an issue, and put in a deep super-insulated basement, to get that free heat and cooling from being linked to the ground temp below frost line.

[badgolferman]

My house is in SE Virginia near the Chesapeake Bay. We do not have basements in this area due to the high water table. The humidity is high in this area. I have a moisture barrier on the ground and insulation between the joists. The insulation has backing on the side that touches the subfloor.

New construction houses around here continue to have crawlspace vents built into the foundation, albeit bigger and more numerous than older houses like mine. The area affected under the house has no vents because it's flanked on one side by the garage and on another side by the porch wall. There is a cutout for pipes to go through the area, but there's really no path for air circulation.

I moved a fan from the porch area to the area that builds up condensation and aimed it toward the other side of the house that is dry and has a fan too. That fan blows toward the foundation that has vents. The fans have been running straight for three days. Hopefully it has dried out enough to remove the condensation by now.

I think I will call the company today and have them perform the spraying that kills everything.

[trader4]

I'd also figure out a permanent solution to getting more air flow in there first. Once they spray it you don't want the environment that created it to still be there.

[jamesgangnc]

I did the bleach trick. Use a vapor mask. The kind you use for painting. I couldn't smell a thing. I still did an area at a time with breaks.

Do you have plastic down? Do that if you don't. Also look at the surronding ground. Try to get the water further away formt the house. Add downspot extensions. The goal is drier ground in the crawl. If nothing else works install a foundation vent fan with a hunidistat outiside. You only want to run the fan when the outside air has a lower humidity. Otherwise you are wasting your time. Just blowing air arund under the crawl will not help much. You need to move the saturated air out and replace it with drier air.

[RogerT]

I think the problem may be that, in your high humidity area, and with between-the-joists insulation that has any vapor barrier (even though it is on the correct side), you are trapping the humidity in the crawl space where it can cause moisture and mold on the floor joists. And, since the outside air is humid, the fans don't change that. If anything, the fans may be bringing in humid air from the outside and just adding to the humidity (and condensation) in the crawl space. You already have a vapor barrier on the floor, which is a good thing. When someone described a situation similar to yours at the meeting/presentation that I attended-- with faced insulation between the floor joists -- the inspector's recommendation was to remove the insulation altogether. Removing the insulation, in his opinion, will enable any moisture in the crawl space to dry out. Keeping the insulation (especially with the facing still in place) keeps the moisture from being able to dry out.

This home inspector is also a licensed structural engineer (or something like that -- I forget the exact engineering title/license he has). Based on everything else he said at the meeting, and the number of years of experience that he has, I was confident that he knew what he was talking about on this crawlspace moisture issue.

I think that the disadvantage of paying a company to spray now is that it doesn't correct the underlying problem and the mold will come back.

[badgolferman]

The company tells me what I need is a crawlspace dehumidifier. They put down new moisture barrier, seal the vents, install a GFC line, dehumidifier and pump all for $3000. That does not count spraying for the wood destroying fungus. The dehumidifier is supposed to dry out the area so much that all the mold will go dormant.

[trader4]

Sounds like a lot of money for the above work to me. I'd find out what dehumidifier they are using and then price it. Unless it's something different than the commonly available portable ones, they only cost $200 or so. Keep in mind with that solution you also have the ongoing electric operating costs.

[jamesgangnc]

Does the moisture barrier include running it up the inside foundation walls to the sill plate? That's the premium barrier and it is a good bit of work to do that. Just laying out new pieces of plastic is not much work and a $100 or so fo rthe plastic. Ask for the brand/model number of the dehumidifier. The price of dehumidifiers varys greatly depedning on what you are getting. Heavy duty commercial ones can be over a grand. So you need more details to judge the value of their package.

[badgolferman]

1. Treat wooden members with fungicide to killl any active fungi.
2. Sealing all Foundation Vents
3. Installing Poly Vapor Barrier (100% ground coverage)
4. Placing a Dehumidifier in the crawl space

[RogerT]

I think that before I spent all of that money and had all of that done, I would try just removing the existing insulation from between the floor joists. The temperatures in Virginia are somewhat moderate, so I don't think that not having the insulation will cause any issues and there is a good chance that it will resolve the problem. I would do that and then check back in a month or two to see what the status of the existing mold is. My hunch is that it will start to go away on it's own without even having to pay to have it sprayed with a bleach solution.

Also, by a GFC line, I assume you mean a GFCI line and receptacle. Where will the water from the dehumidifier go? -- does it get pumped out to the outside of the home?

[jamesgangnc]

That's a pretty expensive dehumidifier so depending on what exactly they do for he vapor barrier install $3k might not be outlandish. Get some more details on how they do the vapor barrier.

[badgolferman]

It seems this option is out. I live in a flood zone and cannot seal my vents. I will have to look at grading problems and how moisture can be minimized. Time for someone else to look at the problem.

[jamesgangnc]

How does living in a flood zone prevent you from sealing your vents? Have you had a flood that entered your crawl? You can do what ever you want. If you have a flood it may change the post flood remediation.

[Tony Miklos]

It sounds like you are at the point where most people would have started. Proper grading and more vents come first. I wonder how much that dehumidifier would have run up your electric bill?

[jamesgangnc]

True, that's the first place to look.

I have problems at our lake house that has been difficult to completely solve with one solution. Putting a house between the rest of the land and a lake is sort of an invitation for a water problems. I've been working on it over the years. I started with lots of drainage pipes taking the downspouts as well as some surface drains all tying into a couple 6" pipes that empty at the low corner lake side of the property. I raised the beds along the house edges, filled them with compact shrubs, and then bordered them with the liriope. Liriope forms a pretty dense root mat that will go down 6 to 8 inches. Lots of "partial" solutions all start to add up after a while.

I'm on Kerr lake which is geographically fairly close to the op. The SE region gets lots of rain and the relative humidity is often high all year. Water is a problem for everyone. Crawl spaces get wet. Shady parts of houses grow mold and algae. Wood rots.