Standing water in crawl space
Tools: flashlight and headlamp, knee pads, gloves and a respirator, submersible utility pump with a hose, shovel and rake, moisture meter (optional) · Materials: 6-mil or thicker polyethylene vapour barrier, seam tape and landscape staples, downspout extensions, gravel
Steps
- Pump out the standing water with a utility pump to the yard well away from the house, then find where it came in — a wet streak down a wall, a plumbing drip, or the whole floor damp after rain.
- Walk the outside: extend every downspout at least 1.5–2 m (5–6 feet) from the wall and regrade low spots so the ground falls away from the house.
- Check the plumbing under the floor for a drip — a leaking supply line or a condensate drain can flood a crawl space by itself.
- Once the floor has dried for a few days, lay a polyethylene vapour barrier over the soil, up the walls 15 cm (6 inches), overlapping seams by 30 cm and taping them.
- If water still collects at one low point after rain, dig a small sump there and set a pump with a float, discharging outside and downhill.
- Check monthly with a flashlight for a month, then each season; the barrier should stay dry on top.
Stop and call a pro if
- water returns within days of pumping with dry weather — that is groundwater and needs a drainage system
- joists or the subfloor are soft, stained black or sagging
- there is sewage odour or the water is grey — a drain line has failed
- the crawl space is too low to move through safely or has visible mould everywhere
Rules in the US: Many jurisdictions treat crawl-space encapsulation with a conditioned-space approach; check whether vents must stay open or be sealed under your code.
What a pro does that you can't
A crawl-space contractor installs interior perimeter drains, a proper sump with battery backup, a sealed encapsulation and a dehumidifier, and a plumber fixes the line that is feeding the water.
DIY cost: $100–300 in vapour barrier, tape and downspout extensions; $150–300 for a pump