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?
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:
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.
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.
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.
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.
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.
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
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
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
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
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.
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?
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
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.
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.
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