I usually am able to lurk and/search or do internet searching to find answers to my questions, but haven’t been successful so far in regard to an issue I am having with the crawlspace moisture problem that I have been having. The structure is an 20×20 two story shed, more like a small house than a shed, that I am turning into finished space. The foundation is fieldstone?, various sized stones in mortar, with a dirt crawlspace under the flooring. Once I did some window and roof repairs it became clear that there was a lot of moisture coming through the floor causing the beginning of a mold issue if not fixed or with no dehumidifier running. There are two vents in the foundation into the crawlspace that have become partially blocked by the grade of the surrounding soil. My plan currently is to re- grade the surrounding soil so that it definitely slopes away from the vents and so that they are clear. Then I will put down a vapor barrier over the soil in the crawlspace attached to the foundation.
My questions, does that sound like a good plan and what exactly do you use for a vapor barrier and to attach it to the foundation. Also would other vents or roof fans help. There is a heck of a lot of good usable space in the house that I would hate to not be able to use due to moisture. All tips and help are appreciated and continued thanks for all of the information that I get through other threads.
Tom
Replies
http://www.rlcengineering.com/csfallacies.htm
http://www.smartvent.net/docs/crawlspacestudy.pdf
http://www.smartvent.net/docs/crawlspacestudy.pdf
I picked the above from various forms of "crawl space" "crawl space vents" etc word combinations on Yahoo.
Couldn't find a really good one I was looking for. Maybe I've got it in favorites.
Did you search the FH back issues? I recall a really good article on this several years back.
It was issue 153.
But apparently that issue was recalled.
Otherwise I can't figure out why it is not in the back issues and appearly never indexed.
That is after I asked about is several times and tried to embarrase the people at Taunton about it.
Almost everyone uses 6 mil polyethylene plastic film sheeting to cover the dirt floor of a crawl space. I prefer black to clear because I think it degrades less over time, and if there is light coming in through the vents, black will prevent any vegetation from sprouting up under the plastic. The only problem with 6 mil poly is that it is difficult to attach to the crawl space walls, as the plastic seems almost to have a oily surface. If you really want to attach it, order Tu-tuff plastic film. It is more durable than regular poly, and can be glued with construction adhesive. This way, you can seal any seams too. The only down side to Tu-tuff is the cost as it is 2 or 3 times the cost of regular poly. You can find where to purchase it via an internet search. Someplace, I think I read that you can use Great Stuff foam in a can as a adhesive too, although I have never tried it myself.
I have a question. You said 2 vents are partially blocked, but didn't really say what the total number of vents was. Just curious.
Also, to help control dampness in the crawl space, if the house has gutters, be sure that the water that exits the down spouts is directed well away from the foundation perimeter. As you already know, proper grading is essential too.
I think they use some kinda dust on the 6 mil to keep it from sticking together or whatever. However one swipe with a rag or pant leg will get enough off so duct tape or spray adhesive will stick big time. And rubbing alcohol after dusting works on wood and rock and ect..
Thanks for all of the info. Once it gets consistently warm out I'm planning to tackle this job, though I'm not looking forward to all of the crawling.
Tom
I should have written "the" two vents as there are only two vents. I took out a tree that was close to one side of the house and that messed with the flow of water so I think that fixing that will help quite a bit. Not having it rain every day this summer will also help. Thanks again.
2 vents is rather minimal. Although a newer train of thought is to not vent at all, my thought is that if you are gonna vent, you need to do a good job at it. Ideally you want a vent on each side, so for a rectangular building that would be 4. With the code we are now using in NC, I believe it now requires a vent on either side of each corner and within 3' of the corner. So, that would be 8 vents on a rectangular building. I'm not suggesting that an older building necessarily needs to be up to current code requirements, and I have no idea of what the requirements are in your state, but you don't get much cross ventilation with only 2 vents, regardless of how they are placed. What I am suggesting is that if you continue to have moisture problems after installing the vapor barrier over the dirt floor and regrading, you may want to add some ventilation. Easiest thing, assuming the crawl space access door is on the side of the foundation (as opposed to one that is through the floor) is to make a new door that is just a frame with louvers and screen, or similar. Another thought is to install a very small blower, maybe even with a humidistat (sp?).Matt
PS: Also, with un-vented crawl spaces, you still need to circulate air via the forced air HVAC system or by other means,
The inspectors here are quite interested in venting and like to see 1 square foot of venting per 150 sf of floor area per code. I have approx. twenty-five vents (I think they're rated at 40 square inches each) into my crawl and a few larger ones under the deck where you can't see 'em. Two vents sounds a little slim.