Home Care Library
Foundation Damp Crawlspace
The Home Wizard app calculates your ideal home care program to avoid problems with your Foundation, but sometimes trouble can still occur. Here are answers to questions about foundation damp crawlspace.
QUESTION FROM Diane Walker
Our NC crawlspace is ventilated and damp. There are no drainage issues, the dampness is from the air and ground. Contractors have proposed two solutions. Which is best? 1. Vapor barrier on floor and walls with dehumidifier. 2. insulated walls(thermax), poly barrier on floor, remove insulation from under floor, vent some air from living space to crawl space. Your help would be appreciated. Thanks!
ANSWER FROM HOME-WIZARD
Its difficult to say exactly without being able to physically examine your house, for example, to see the size of the crawlspace relative to the size of your living space, and to see how the crawlspace is currently being ventilated, etc.
But from what you described, if your problem with your crawlspace is that it is too damp, I would lean towards your first option of adding a vapor barrier on the floor and walls and using a dehumidifier (which would help separate the crawlspace from the living space, and then deal with the humidity problem in the crawlspace), rather than the second option of removing the insulation under the floor and venting air from living space to the crawl space (which would essentially be integrate the crawlspace with the living space).
The risk of the second option is that you are not reducing the humidity of the crawl space, rather, you are potentially moving it into your living space by somewhat connecting these spaces together (i.e., insulating the crawlspace walls and floors, but removing the insulation under the floor and allowing air from the living space to vent into the crawlspace area).
A couple of other thoughts that you might want to also consider:
1) when you say the crawlspace is ventilated but damp, is there anything that you can do to increase the ventilation of the crawlspace to and from the outside?
2) have you checked to see if there is air from the living space that is getting into the crawlspace? If you have warm air from a shower/bathroom or kitchen fan vent pipe that is leaking into your crawlspace, then when this warm air hits the cold crawlspace it can cause condensation / humidity. Similarly, if you have poor seals (weatherstipping, cracks, etc.) between your living spaces and your crawlspace, then this can be another way that warm moist air can cause condensation / humidity in your crawlspace.
3) there is also a cost tradeoff for essentially having more living space conditioned air (the air that vents into the crawlspace area), versus running a de-humidifier.
But again, its difficult to exactly say which option is better without being able to see specifically what your situation looks like.
Hope this is helpful.