humidity control question

[Phil S]

I store my wood under my house in a "crawl space" that is about 1500 sq ft with six foot headroom. I have the wood stored on racks above the dirt floor. It seems to be dry yet when I checked the wood today with moisture meter it showed 15 - 16%. What would be the best way to reduce this level of moisture? Would covering the floor with 6 mil poly help or would I be better off with a dehumidifier? I am assuming I should be storing this wood at about 10 to 12% and I do not store any green wood there - I dry green wood in my garage. Thanks for your help

 

[DaveO]

Crawl spaces tend to be places with little ventilation. So 15-16% MC is probably right in line with reaching EMC with our humid summer environment. I doubt that you are getting much moisture migrating out of the ground. Lack of air flow is probably your biggest issue. Some fans to move air and a dehumidifier to lower the RH and raise the temperature should definitly help.
I have a basement shop with little natural air flow. I run a box fan 24/7 to keep the air moving around. It is tied into my house air system so I get "conditioned" air down there which helps to lower the RH. I also run a dehumidifier 6 hours on, 6 hours off. I can air dry lumber to around 10% in those conditions.

Dave

 

[Joe Scharle]

I don't know how you got a CO on your house in Wake county without the moisture barrier!
The clay base around here pretty much requires one, so as Dave says, a fan plus moisture barrier should help you a lot.

 

[Phil S]

I don't know how you got a CO on your house in Wake county without the moisture barrier!
The clay base around here pretty much requires one, so as Dave says, a fan plus moisture barrier should help you a lot.

I am not sure if a moisture barrier was required in 1979 when this house was built. When I moved in fourteen years ago I put some plastic in one area and it has never been moist underneth so I thought it wasn't doing much, plus I hate walking on the slippery plastic. As my air handler system is in this space, I am thinking about cutting in a return and a few supply vents to help dehumidify during the summer. With that, do you think I should still install a vapor barrier and if so do you know of a type that is not so slippery? Thanks

 

[dancam]

Phil,

From my experience the vapor barrier (poly) will only be effective if you cover all the ground. Some folks say to even cover up the wall (partially to about 2-3 feet) with the poly taped to the wall.

Running a dehumidifier could become very costly energy wise. Running a vent fan with a humidistat would most likely be more cost efficient. The added benefit to all this would be to prevent moisture migration into the house.

Dan C.

 

[Joe Scharle]

Phil, here's a starting point for reading up on crawl space control.
http://www.askthebuilder.com/B109_Crawl_Space_Ventilation_Tips.shtml

BTW, a few years ago I was a home inspector and inspected a home in N. Raleigh that the owner had used the tall crawl space as a large dog house. The poly was clawed to pieces and he had also shut the vents. The band joist in the low corner had rotted, along with 2-3 floor joist ends. House was 8 years old! French drains aren't infallible.

 

[Glennbear]

In addition to the sage advice given by Joe and Dave I would recommend against tapping into the air handler. The air handler was likely sized to match the volume of your house and to add the load of the crawl space area might not be the best idea. :wsmile:

 

[SteveHall]

The conventional wisdom of ventilated crawl spaces is being supplanted by science: Closed Crawl Spaces. Basically, if you control the humidity (vapor barrier) and temperature (insulation) the moisture levels will drop to those of the building's interior. An ideal condition to dry lumber!

Otherwise, there isn't any way to generate enough air turnover or sufficient moisture extraction to avoid the conditions that encourage mold, short of putting a full-time HVAC unit in the crawl.