How often should you inspect a crawl space?

Short answer

Inspect the crawl space twice a year, and after any heavy rain or flooding. A crawl space is the shallow space under a house that has no basement, and it's where water, mold, pests and cold air all start their work on the floor above. Going in with a flashlight and looking at the ground, the joists and the vapor barrier takes 20 to 40 minutes and costs nothing. A professional inspection runs $100 to $300.

Why it matters

The crawl space is the house's underside, and it's damp by nature. Moisture rises from the soil, rain runs in from outside, and the air down there is cool and still. That's the recipe for mold on the floor joists, which are the wood that holds up every room above. It's also the recipe for wood rot, for termites, which love damp wood near soil, and for rodents, which find a crawl space the easiest way into a house.

What happens in the crawl space comes up through the floor. Damp air rises into the rooms and brings the musty smell with it. Insulation that's fallen from between the joists leaves the floor cold in winter and the energy bill high. A vapor barrier that's torn or missing lets the soil's moisture into everything. A twice-yearly look finds the standing water, the fallen insulation and the first mold while they're small, and after a heavy rain it tells you whether the drainage outside is doing its job.

When to do it more often

The index gives one modifier: heavy rain or flooding. Go in afterward and look for standing water and wet soil, because water that got in once will get in again, and the fix is outside, in the grading or the gutters. Beyond that, go in when the floor above feels damp or smells musty, when a room's floor turns cold in winter, and before and after any pest treatment, to see what the treatment found.

What you need

A bright flashlight, or a headlamp that leaves your hands free
Coveralls, since you'll be on your stomach in dirt
A dust mask
Knee pads

Steps at a glance

Open the access hatch and shine the light in before entering, looking for water, animals and anything that shouldn't be there.
Crawl the length of the space and check the ground for standing water, wet soil and the state of the vapor barrier.
Look up at the floor joists and the subfloor for dark stains, fuzzy growth, and wood that looks damp.
Check the insulation between the joists for sections that have fallen, sagged or gotten wet.
Look for droppings, nests, insect activity, and mud tubes on the piers and foundation walls.
Check the vents and the hatch for gaps and damage, and look at any pipes and ducts for leaks and loose connections.

You're done when you've seen the whole space and found dry soil, a whole vapor barrier, clean joists, insulation in place, and nothing living there.

Signs it's overdue

Standing water, or soil that's wet to the touch.
A musty smell in the rooms above.
Insulation sagging or fallen from between the joists.
Mold on the joists, as dark patches or a white fuzz.
Droppings or nests.
A vapor barrier that's torn, bunched up or missing.

DIY or pro

This is a moderate job, and the moderate part is the crawling. The space is low, dirty and sometimes wet, and a headlamp and coveralls make it bearable. The inspection itself is simple once you're in: look at the ground, look up at the wood, look at the insulation.

A professional inspection costs $100 to $300, and a crawl space company brings moisture meters and knows the difference between surface mold and rot. That's worth it if you can't fit through the hatch, if the space is flooded or you suspect it has been, or if an inspection turns up mold or soft wood and you need to know how far it goes. Mud tubes on the piers are a termite inspector's job, and the sooner the better.

Safety

Structural: a crawl space with rotten joists, soft subfloor or undermined piers is a space where the house above is losing its support. Don't push on or hang from damaged wood, and if you find joists that are soft or sagging, have a contractor look at them before anyone does heavy work on the floor above. Keep the hatch open while you're in, and don't go in alone if the space is flooded or the air smells of gas or sewage.

FAQ

What should I look for in a crawl space?

Standing water, wet soil, a torn or missing vapor barrier, mold or stains on the joists, fallen insulation, droppings and nests, and mud tubes on the piers.

How do I know if my crawl space has moisture problems?

A musty smell upstairs, water or damp soil underneath, condensation on pipes and ducts, and mold on the wood. A vapor barrier over the soil and working gutters outside are the usual fixes.

Should a crawl space be inspected after it rains?

After a heavy rain, yes. If water got in, you'll see it then, and the cause is outside: grading that slopes toward the house or gutters that dump beside it.

Is mold in a crawl space dangerous?

Mold on the joists means the wood is staying damp, which leads to rot and feeds the air upstairs. Fix the moisture first, then have the mold cleaned.