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Crawlspace Q's and A's

Eliminating Moisture/Odor | Other Moisture Problems | Ventilation | Other Issues
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Eliminating Moisture & Smells


I have a couple of problems with my crawlspace
1) There is some moisture around the support pillars mainly in my crawlspace but not enough to use a sump pump. How do I get rid of the moisture?
2) I think the smells from the crawlspace come up through the ventilation(the furnace is in the crawlspace). How do I get rid of the smells or keep it from coming up into the house?

The first thing to do always, is cover the dirt floor with 6 mil plastic sheeting. overlap any seams (and tape them even) and run it right up to the walls. There is a lot of moisture that comes up from the floor.. and that moisture supports the mold and mildew that cause the smells, (not to mention the rot of your wood if it is bad enough)

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This Old, Stinky, Mildewy House

I live in a rambler on a crawl that was built 50 years ago. We remodeled the inside of the existing house and built an addition on to it. After getting new carpet throughout, the floor in the old portion of the house seems to be emitting a mildewy odor. When the house was remodeled, plastic was placed in the crawl and the insulation value was increased. Under the carpet are some old tiles that look to be almost as old as the house. My suspicion is that the crawl space was not insulated well and had no plastic in it until about a year ago caused the wood subflooring to mildew and the smell has resurfaced through the new carpet. I want to rid myself of this odor. Can I get away with stripping the tiles, applying a sealer to the sub-flooring, and reapply something like linoleum, hardwood floors, to get rid of this odor once and for all or do I need to take all of this sub-flooring out?

If the wood dries out and should with the plastic down in the crawlspace, you may be able to get away with just sealing the floor and recarpeting.
If you can run a dehumidifier down there to keep it dry that will help to.
Another idea if you have access to the crawlspace is to pour a cement floor in there on top of a plastic barrier. That would eliminate the moisture for sure.. and I am for eliminating the source.. because I think the stink will cease if the wood finally dries.


Damp Walls in Basement

I have a 35-year-old house I just purchased. It has a dirt floor in the crawlspace and a concrete floor in a part that was added ten years ago. There is a sump pump in the newer part. The problem is this, in the portion of the basement, which is just a crawlspace there seems to be water "wicking" up the concrete walls. Is there a way of preventing this? I am worried that some of my floor joists will rot if this continues. Can anyone help me with this?

Concrete will pass water, but I haven't known it to wick it up. Tell me, are the wet areas ABOVE the grade level outside? My guess is, that it is showing wet where there is a water problem outside in the ground. Another idea is that it is water condensing on the surface of the concrete from the moisture inside and the cold wall. You should eliminate the source of the water and or moisture.

For the inside, cover the whole dirt floor area with 6-mil plastic . Go from wall to wall, and overlap well and even tape the joints in the tape. Seal the tape all the way around the outside as well. You can run it up about a foot along the wall and stick it to the concrete with an adhesive (like roofing tar in a tube so you can use your caulking gun, or LiquidNails).

For a water problem outside, make sure the ground has a gentle grade away from the house. Make sure your gutters drain away from your foundation. I don't believe that the water will not work its way up to the joists, but the moisture if it is significant IS a problem of the same sort. Capable of causing dry rot.





Ductwork sweating under crawlspace


I installed new insulation on 75% of my ductwork in the crawlspace of my home. The insulation was about 1" think, with a "Reynolds wrap" color outside paper, the insulation was yellow in color. About two months later, I'm in the crawlspace preparing for my inspection tomorrow, and noticed that all of the new insulation is sweating. I live in VA and its not unusual to have humidity in the 90%+ range.
The location of the sweating ductwork is such that the drips will only fall on the vapor barrier already in place. No wood is at risk as it hangs on hangers from the floor joists. Is this a problem, considering all that, does it need to be addressed? If so, how?


Since the water isn't dripping on anything on your home's structure, or puddling in anyway that could cause damage, then I think the water is not a problem. Some things to consider: You have vapor barrier over the whole floor? Is it a dirt floor? That is one way to reduce the humidity in the crawlspace... cover the floor, from wall to wall with a 6 mil poly vapor barrier (I am thinking you have that?) Also, make sure the vapor barrier is as tight as it can be on the duct.. or the moisture will wet the insulation rendering ineffective. Otherwise.. if the humidity is high enough.. and the duct temp below the dew point.. it will condense.. nothing you can do but add more insulation. You can run a dehumidifier in the crawlspace to lower the humidity down there.


Visqueen in crawlspace

Can putting visqueen in a crawlspace be a do-it-yourself project? Crawl is only about 3 feet high. What is the importance of not doing it. We aren't currently experiencing any moisture intake within the interior of the house. And, what time of year is best to do it?


Well that can be done your self, certainly. And it can be done any time of year. It is always a good idea to prevent moisture from coming up into the house from the ground. There may have already been a good vapor barrier installed under your floor when they insulated the floor. (Is the floor insulated?)
In any case, it is inexpensive to roll out some 6 mil plastic covering the floor completely, overlapping any seems (and taping them shut helps even more)


Crawlspace Moisture

After a termite inspection noted high moisture, I began to install additional moisture barrier (plastic) in my crawlspace. About half of the crosspiece already had plastic in place. I noted that all of my duct work insulation was dripping with water and low areas of my floors were wet. What are my options to improving moisture problems.

You have begun the best thing you can do... finish covering the dirt with plastic. Overlap the seams .. weight everything down, and you should cut the moisture problem significantly.



Wet Crawl Space

I have a small area measuring 8ft long by 4ft wide and max 1/2 inch deep that is filled with water. This area is not one solid area, it's a combination of many small shallow puddles. Living in a saturated water table of Seattle, I don't think this needs a sump pump because it seems minor. The downspouts are clear. Any suggestions for a remedy?

Can you trench a perforated pipe and feed it on a downward slope to an area away from the house?

I like Ranie's idea best.. no pump .. just a drain to daylight. But if your lot is level... then I would go with a pump. You shouldn't let water set under your house.

Frost Build-up in Cold Cellar

Our house is 9 months old and as the weather has gotten colder, we have noticed frost building up in the cold cellar, which is below the entrance stairs to the house. In the summer, the room was humid. We also noticed the room has no vent. Should the room have a vent and how can we stop the frost/humidity problem?

What is on the floor? And the walls? If they are dirt, I would suggest covering them with a layer of 6-mil poly sheet. Seal them up tight to keep the moisture from coming through. Is there an adjacent cellar? If so, run a dehumidifier down there. I would try to NOT use a vent or your cold cellar will be a freezer in winter, and NOT cool in summer. You can run a dehumidifier right in that space.. but it may add too much heat for your liking...

Crawlspace Ventilation Fan for Moisture Control

During annual termite inspection, it was noted that there was wood fungus on floor joists due to high moisture levels. It was recommended to apply a fungus killer and install power ventilation (3 fans). Question is can a homeowner due this as far as applying the fungus killer and where do you get the fans for this application. I prefer placing one that has louvers and is mounted in the crawlspace foundation in an opening of 18" X 18".

If you are handy with tools and electrical wiring you can install this system yourself with a little planning. The parts you'd need (including ventilation fans) are available at most large home centers, although for your problem I would probably go to a HVAC contractor/outlet. The system of ventilation would be controlled by a humidity control unit that would come on/off according to moisture levels.
I would be very concerned that you have so much moisture under your floor joists. If you know the cause of the moisture levels you should go to the root of the problem and correct it (e.g. failed or no drain tiles around your foundation). But if there is minimal options you need to certainly get on with doing something to dry the space under your floor.

Crawlspace Vents: Open/Closed

Is there a general time of year when the vents in a crawlspace should be open or closed? My wife and I recently built a log home in southern Indiana and have heard mixed opinions. I realize it depends on excess/lack of moisture under the house, but is there a rule of thumb?

Vents are designed to remain OPEN at all times. Many codes require this for radon gas mitigation.

More

Anyway, this is actually a timely question for me too. I have a crawlspace for half the house (about 30'X30') and a finished basement for the additional 30'X30'. The crawl space is separated from the finished basement by a cinder block wall. A "half" door (just plywood) is used for access into the crawl space. Since I live in Atlanta, we can get a lot of humidity. The dirt is covered with a vapor barrier (Well most of the dirt. It is kind of a poor job) and there is only one vent (East side). The inspector said another vent was needed but due to the way, the house was constructed that this was impossible.

Therefore, I am now in need of at least a screen over the vent (Keep some of the Roaches and other critters out!) but was wondering if I should install a crawlspace fan. The basement does seem to be humid (Not official, just gut feeling). Moreover, I'm wondering if I should install a fan. I'm not familiar with vents in crawlspaces so should I bring air in our vent air out.

Ventilation is both in and out. That was why the inspector said you need another vent. One to let air in, one to go out. First, I would make sure the plastic job is corrected. Cover the whole floor... wall to wall. Overlap and even tape any edges. You can even seal the plastic to the walls for an even tighter seal.
Run a dehumidifier in the basement. That will cost something to run of course, but it is worth it.
If you can't install another vent, try this. Seal the vent shut and cover all the walls with plastic. Staple it right to the sill plate on top of the wall and cover the walls taping the bottom of the plastic to the plastic on the floor. If you can seal the moisture out of the crawlspace, ventilation becomes unnecessary as long as you have no radon problems. (You can buy a kit to test for radon after you seal it up.)

Insulating Front entry/foyer crawlspace



I own a 60 year old cape with a foyer that has its own foundation attached to the house. I am replacing the front door and frame to take care of a rotted sill. Besides putting plastic on the dirt floor, I would like to insulate under the floor. The space is not vented. What would be a good choice of material?

Fiberglass batts between the joists will work best. Even though it is not vented and you are putting plastic down, use a vapor barrier (towards the floor, facing up) if the space is or ever will be heated.



Cementing Over Crawlspace

Like my crawlspace - concrete chunks, rocks, wood, beer cans, else over and under poorly kept laid vapor barrier. I was considering doing drain tile/sump pump - I live within a couple hundred feet of a river but since there is no structural damage at all, I will just try cleaning out debris and fully relaying vapor barrier. Anyone heard positive or negatives to cementing the floor in. I have a 4.5' crawlspace so it's a possibility....

I have seen crawlspaces cemented over with good results. Lay 6-mil poly under the concrete to seal out the moisture, and then you have a nice flat, dry area for storage.



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Click here for our How To Keep Your Basement Dry Article
Click here for our Basement Tips Article
Click here for our Moisture In The Home Article
Click here for our Dealing With Condensation In The Home Article



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