A puzzle: Moisture Mitigation and Energy Efficiency in Inaccessible/Unconventional Crawl Space
Hello–apologies for this long post. I have an unconventional, puzzle of a problem.
Our house was built in the early 1900’s in zone 3c (Sacramento, CA) and has an inaccessible, dirt (heavy clay is the natural soil here–aka slooow drainage), and marginally vented crawl space. I think the original house was built directly on the ground, and then overtime the ground level around it was raised, rather than an excavated crawl space. The crawl space has anywhere from 12″ to 24″ inches of clearance between bottom of floor joists and dirt floor, and there’s old railroad ties in some places (not touching current joists) that would further obstruct movement of a person. The house is 1,100 sf with only three 12 in. x 4 in. vents.
We’ve had the subfloor open in several spaces for the past 2+ years to fix major wood rot and termite damage issues and to redo plumbing. This has allowed us to observe the problem.
Moisture! mostly around the interior perimiter. We used various sealants and caulking to fix all cracks in the stucco siding and sidewalk walkways. We thought this would solve the problem; however we’re still seeing moisture in the soil. Based on the floor pattern of the moisture, I believe this is ground water. We have not seen any pooling, and this year brought very heavy rains, including the highest single-day rainfall on record during which we did not have gutters. Still no pooling.
Goals (in order of importance)
1. Stop woodrot and mold.
2. If mold can’t be avoided in this situation, keep it from seeping upwards into the living space and walls.
3. As best as we can in the situation, insulate the floors for energy effiency.
1. I think the “right” answer is to jack the house up so there’s an adequate crawl space, we can condition it, etc. This is not financially possible for us.
2. I think the second-best “right” answer is to remove all the subfloor and do our best to lay down a plastic vapor barrier. However, we’ve already replaced most of the subfloor in the house as the prior owners had a hoarder/critter problem and the old OSB was soaked in dog/mice urine. Subfloor is T&G 3/4″ ply that was attached with liquid nails, so I think it would be extremely wasteful to rip all this up. Not to mention current inflation on wood.
Things we’ve considered and questions:
1. Given this is mostly a moisture issue and not a pooling issue, would a commercial style dehumidifer (or 2) be sufficient? I am considering building a raised box in the subfloor in 1 or 2 closets where the dehumidifer could sit in the crawl space, otherwise, I don’t think there’s enough floor clearance. I think this would only be needed during a few winter months.
2. What about fans in the crawlspace? I am considering the fans linked below and building hatches in the floor where they are located so we can access them if they break: https://www.acinfinity.com/hvac-home-ventilation/crawl-space-basement-fans/airtitan-t3-crawl-space-and-basement-ventilation-fan-6-temperature-and-humidity-controller-ip-44-rated/?gclid=Cj0KCQiAq7COBhC2ARIsANsPATEdJ-HCumWx8oAS2mhLf9ts2VR31tl9RljrM7KZWNNxfiQkC6LElgIaAntBEALw_wcB
3. Should we seal up the three piddly vents? If so, how will we get sufficient airflow to remove moisture? Will sealing up the vents create condensation or other issues? Should we go fully the other direction and add a ton more vents since they can only be about 4″ high?
4. For insulation, I’m planning on “air sealing” the spots where subfloor meets wall sill plates, and over the sill plates with caulk, foam, or some kind of tape. Any suggestions? Also considering laying down some thick cork for temperature control with a moisture barrier attached. Any suggestions?
5. We have gutters. Anything else we can do outside?
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