Crawl space dampness

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  #1  
Old 11-03-14, 10:43 AM
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Crawl space dampness

Have a damp smell/feel in my crawlspace that I think I should do something about.

House is 40+ years old in PNW and had issues with wet crawlspace long before I purchased house, previous owner dug out a drainage path and installed a plastic vapor barrier [so corrected].

After 10+ years of owning the house, don't currently see any issues [i.e. mold, standing water, etc] but, think I should probably do something to remedy the smell/feel.

Space is about 180 cubic ft. [20x30x3]

During the summer, I just leave the door to the crawlspace open for cross ventilation but, the wet fall/winter/spring makes that a bit harder.

I would describe the issue as more annoying than troublesome at this point and not sure if using a humidifier would be more efficient/effective than a product that passively dries the air.

Looking for suggestions on a route to take.

Thanks

edit: the furnace is in the crawlspace but, is piped to bring in fresh air [as well as return air from house].
 
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Old 11-03-14, 01:04 PM
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What kind and how much ventilation does the crawlspace have?
I'm of the old school train of thought where you provide vents throughout the foundation. That's how my house is done and my air handler is also in the crawlspace. I don't have any moisture issues. Some now think you should seal the foundation up tight and condition it with the rest of the house [HVAC vents] You'd probably want to use a humidifier if you sealed the crawlspace up.
 
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Old 11-03-14, 01:09 PM
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Fresh air is old school that doesn't work. Close those doors and vents. The VB must be sealed to the wall an inch our so from the seal plate. All seams need to be sealed. Rarely or dehumidifiers needed when this is done correctly.
 
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Old 11-03-14, 01:23 PM
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Fresh air is old school that doesn't work
While I might agree that fresh air ventilation isn't always best - it does work if there is enough ventilation. My crawlspace is super dry, the only moisture that ever been in my crawlspace was when there was a plumbing leak.
 
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Old 11-03-14, 09:32 PM
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Since tpring lives fairly close to me (I live just past the King-Snohomish county line) I may have some insight.

Most of the homes built in the last fifty years or so in the Puget Sound Basin have ventilated crawlspaces; that is, if they don't have a full basement. Because of our West Coast Marine climate we have a fairly moderate temperature profile year round and also a fairly moderate relative humidity profile. What that means is that high temperatures during the summer rarely exceed 90 and low temperatures in the winter rarely drop much below freezing. (There ARE exceptions!) Now the bad thing is that during the rainy season, roughly from October through May (No, I'm not kidding) the temperature is high enough that the relative humidity inside our homes is often in the 60% or higher range. Outside RH is often in the 80% to 99% range. Having a ventilated crawlspace will allow the air with 99% RH into the crawl and then because there is no temperature difference with the outside there is little, if any condensation.

However, if the temperature then drops the air in the crawl becomes saturated (with moisture) and condensation WILL occur until the RH and temperature again come into equilibrium. Having a dirt floor in the crawlspace makes matters worse. The ONLY thing to be said for a ventilated crawlspace is that it is cheap to construct. That is one of the reasons why the Washington State Energy Code REQUIRES so many vents for a crawlspace, to make darn sure there is a large flow of air through that space.

Ideally, the crawlspace should be sealed from the great outdoors to the same extent as the living areas of the house. The exterior walls should be insulated to the same level as the living areas and there needs to be a controlled airflow from the heating/cooling plant through the space as if it were a living space; in short it should be treated as a low headroom basement. The biggest downside to this is the cost. If you are going to go to the trouble of having the crawlspace sealed properly during new construction then in my opinion you should go the full route of having a basement installed. The cost will be minimal for the amount of usable space gained.

Whether or not to seal an existing crawlspace is much harder to determine on a cost/benefit analysis. Sealing a typical crawlspace could run $10,000 or more depending on the area and the difficulty of working in the space. The returns are such that payback may not even begin for twenty years but you will have a nicer environment.

One more thing, while it is unnecessary to insulate the overhead in a sealed crawlspace (you DO insulate the walls) insulating of the overhead IS necessary in a ventilated space. It seems, at least in this area, that fiberglass is the insulation of choice and in my opinion fiberglass has nothing to recommend it other than price. Although it doesn't actually provide any food source for vermin it IS a dandy nesting area for mice and other rodents. It does not stop air currents, it can get waterlogged and lose much of its insulative properties from the high humidity often prevalent. It has no natural resistance to moisture flow and depending on how it is installed it can easily fall out of place. Two-pound density closed-cell foamed in insulation would be ideal but there are VERY few insulation contractors that would install spray foam in a 34 inch crawlspace without adding a hefty premium to the already high price of the product.
 
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Old 11-05-14, 07:17 PM
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Thanks for the replies.

The area has only 3 vents and one of them is being used to pipe in the fresh air for the air handler [done by previous owner] -- so effectively only 2 and, they are at the far end [east side] of the crawlspace. This makes for almost no cross-ventilation. And it seems to me that this space is relatively comfortable [temperature-wise] whether it is 'cold' or 'hot' [these are relative terms] outside.

The crawlspace is actually about 1/3 dugout to about 6 feet with the rest being about 18".

While turning the crawlspace into a 'basement' is enticing, I don't think it is going to happen -- We have discussed the idea of digging it out [for storage/work space] but, don't want to compromise the foundation -- Plus, digging it out would also require installing a beam to replace all the supports through the centerline.

For now, I just want to prevent any dampness issues.
 
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Old 11-05-14, 10:01 PM
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Here's some reading from building science corp.
BSI-009: New Light In Crawlspaces — Building Science Information

Bud
 
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Old 11-05-14, 11:58 PM
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For now, I just want to prevent any dampness issues.
Dampness issues in our area are pretty much the price we pay for living in such a beautiful place. If you give me a better location (what city are you in or is closest to where you live works) I may have some more specific advice.

You MUST have a ground cover of at least six mil plastic over any bare earth. Best to have it overlap a foot or so at all seams and all seams taped as well as the plastic run up the footing/foundation wall to at least outside grade level and then sealed but very few in this area are installed to that level. Just make certain that the vast majority of the soil is covered will help tremendously. Be certain the surrounding yard slopes away from the house to reduce hydraulic pressure against the walls from rainwater in the soil.

Your venting is VERY poor. You need cross ventilation if it is going to work at all. On the other hand, if all you have are three vents you can seal them up easily and hope for the best. With sealed bents and a plastic ground cover you could run a dehumidifier as needed although it WILL have both a capital cost for the unit as well as ongoing costs for electricity. Up side is that you only need to bring down the RH to a point where it is no longer a condensing atmosphere. If you have no ceiling insulation in the crawl then the heat transfer from above may be all that is necessary.
 
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