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Full crawl space encapsulation versus just a thick vinyl liner

justincase123 | Posted in General Questions on

I have a 20 year old house in South Carolina with a crawl space that I’ve lived in for a little over 3 months. The house currently has a 6 mil vaport barrier that is in pretty bad shape. Since then our area has had record rain and above average temps/humidity. I’ve checked under the house every few times it has rained and things usually looked ok. Fast forward to last week when we had another round of heavy rain and above normal temps I check under the house and it is absolutely soaked with water dripping from the piers, fiberglass insulation and beams. I also noticed a few spots of mold forming on the joists. There isn’t water running into the foundation anywhere so I guess it is just from the humid air.

The first company I called out specializes in encapsulations. He was there while it was still actively raining and saw the issues I noted above. He didn’t even go into the crawl space but checked the wood moisture which was between 18% and 20%. His recommendation (obviously) was to remove the batt insulation, close up the vents, spray foam the walls, install a 20 mil liner, and open up the air handler to let in conditioned air. The quote for this was $6,000 which from my research doesn’t seem unreasonable.

The second company I called is who I have my termite bond through that also works with moisture/foundation issues. He came out a few days later after everything had dried up and spent about 15 minutes crawling through the inside. By this time everything was dry under the house and the moisture readings were below 15%. He said they could also do an encapsulation but didn’t think it was necessary and instead recommended installing just a 20 mil liner. The quote for this was $1,500.

So obviously I have two very different options with very different prices. A part of me wants to just do it the right way and fully encapsulate, especially since this will not only help with moisture but also the insulation. The thicker liner is a lot cheaper and I suppose if I change my mind down the road I could always just build off of the liner and add spray foam. Anything I’m missing?

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  1. GBA Editor
    Martin Holladay | | #1

    If you want to convert a vented unconditioned crawl space to an unvented conditioned crawl space, do it right. The right way includes wall insulation.

    Here is a link to an article that explains all of the required steps: Building an Unvented Crawl Space.

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