Crawlspace moisture check
Twice a year · typically May and November
Why it matters
Out of sight is exactly how crawlspace problems get expensive — nobody looks until a floor feels soft.
What skipping it costs
$2,500–$15,000
A wet crawlspace doesn't stay a crawlspace problem. Moisture wicks up into joists and subfloor — cupped hardwood, musty rooms, then structural rot. Repairs start around $2,500 for sistered joists and run past $15,000 when beams go. The floor you walk on every day is standing on whatever's happening down there.
Two ways to get it done
Do it yourself
You'll need: Bright flashlight or headlamp, Old clothes, Phone for photos, Cheap hygrometer (~$12, optional but worth it).
- Go in May and November — after spring rains, and before winter shuts everything up.
- From the access door, sweep your light across the whole space before crawling. You're looking for: standing water or staining on the plastic, sagging wet insulation, and white or green fuzz on joists.
- Check the vapor barrier (the plastic sheeting on the ground). It should cover the soil with seams overlapped. Bare wet earth under your house is a humidifier running 24/7.
- Touch-test a few joists near the perimeter. Solid wood feels like furniture; trouble feels soft or damp.
- Look at plumbing runs for drips, and at the duct insulation for condensation.
- If you bought the hygrometer, leave it down there and check it each visit: sustained relative humidity above ~70% in summer means the space needs help.
- Photograph the same spots every visit. Change over time is the signal.
Hire it out
$100–$250National fair range — local labor moves this number.
If crawling under the house is a hard no — fair — a standalone crawlspace inspection runs $100–$250, and pest-control companies often do a version of it cheaper as part of a termite contract.
Here's the trap to avoid: the free inspection from a crawlspace-encapsulation company. Free inspections from people who sell $12,000 fixes find $12,000 problems with impressive reliability. Get the assessment from someone who doesn't sell the cure — a home inspector or your pest contract tech — and if they flag real trouble, then get encapsulation quotes plural.
Ask the tech
- What's the actual moisture reading in the wood, and what number would worry you? (Under 15% is fine; sustained above 19% grows things.)
- Is the vapor barrier intact and lapped, or does it need repair?
- Can you photograph everything you're describing? I'm not coming down there.
Red flags you're being upsold
- A $15,000 full encapsulation pitch on the first visit for a crawlspace that's merely damp. Encapsulation is a real fix for a real problem — it's also the most oversold product in residential construction.
- Mold panic language. Surface mold on a few joists is common and treatable for hundreds, not tens of thousands.
- A dehumidifier sale without fixing the water source first. Drying the air while water pours in is a subscription, not a solution.
Second opinion time: Any quote over $3,000. Crawlspace companies price against your fear of the dark — a second opinion routinely comes in at half.
The call
DIY the looking twice a year — it's unpleasant, not hard. Hire the fixing, and never from the first company that quotes you.