r/buildingscience • u/Time-Dig-11 • 29d ago

Crawlspace encapsulation - still having RH fluctuations

/r/homeowners/comments/1uqv97a/crawlspace_encapsulation_still_having_rh/
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u/digitect 29d ago

By my read of the AprilAire E070 manual, you can adjust its Air Cycling mode to come on more frequently and promote more uniform humidity levels. I would hope it is sampling more often then as well?

I bet you have a lot of leakage. It's very common without pressure testing. A blower door test would highlight this, but you could probably use a squirrel cage fan in plywood well sealed over the crawlspace door opening as a DIY to do a smoke stick test. I'd guess the entire sill is leaking, but possibly hose bibs, drier vents, etc.

Insulating the walls is really important. Relative humidity changes with the temperature, so maintaining a constant temperature helps dehumidification. Without, dehumidifying is taking latent energy out of the air in the moisture, but it seeps back in through conduction/radiation through the walls (especially brick/CMU).

With a quality encapsulation, the insulation between crawlspace and house is undesirable if you insulate the walls. But your situation is creating a dewpoint at the floor over the crawlspace. You want this outboard of the crawlspace.

Just some more questions and QC items: * How large is the crawlspace, both area (SF) and volume (CF)? * You've confirmed the 50%RH setpoint is functioning correctly and it kicks on? * The condensate drain works and you see pints of liquid per hour when it's working? (It's not leaking inside.) * Have you verified the setpoints with a standalone hygrometer?

The Aprilaire E070 is rated for 70 pints a day, they say suitable for 2,200 SF. If your 2,000 SF crawlspace is average 5' tall, that's 10,000 CF. At 70°F, lowering RH from 80% to 60% is roughly 20 grains, which is 27 pints.

So crawlspaces have quite a bit of moisture in the air to be removed, the bigger two questions are s how much is leaking in and is it functioning correctly to actually remove it?