Why Crawl Spaces Get Wet in the Pacific Northwest and Fixes

Crawl spaces exist all over the country, but the Pacific Northwest gives them a hard time. Most of our rain falls from fall through spring, and it often falls for days in a row. The ground stays soaked for months. In many neighborhoods, especially near lakes, creeks and low spots, the groundwater sits close to the surface in winter.

At the same time, our winter air is cool and damp. Even when it is not raining, the air outside often holds a lot of moisture. Research by national labs on Northwest homes has found that crawl space moisture is closely tied to the soil and the outdoor air, not just to leaks.

1. Gutters and downspouts

One downspout can dump hundreds of gallons of water next to your foundation in a single storm. If it does not carry water away from the house, much of it ends up under the house.

2. High groundwater

In wet months, water can rise up through the soil and seep in through the floor of the crawl space. Homes near water, like those in Yarrow Point and Juanita, see this often.

3. Yard slope toward the house

If the ground slopes toward your foundation, rain runs to the house instead of away from it. This is common on hillside lots.

4. A torn, thin or missing vapor barrier

Most crawl spaces have a plastic sheet over the soil. When it is torn, bunched up or missing, moisture from the soil rises straight into the space.

5. Plumbing leaks

Supply lines, drain pipes and water heater lines often run under the floor. A small drip can soak insulation and soil for months before anyone notices.

6. Condensation

Warm, damp air meeting cool pipes, ducts or the underside of the floor leaves water droplets behind. Over time this wets wood and insulation.

• A musty smell in the house, worse when the heat is on.
• Cold or soft floors, or floors that squeak more than before.
• Cupping hardwood with no leak above it.
• Sagging or falling insulation under the floor.
• Standing water, mud or a white powder on foundation walls.
• Higher allergy symptoms indoors in winter.

A wet crawl space can also feed mold on joists and subfloor. Read how fast mold grows after a leak.

Many homeowners never look under the house. Twice a year, after a big storm in fall and again in spring, take a quick look.

1. Turn off power to any equipment in the crawl space first.
2. Use a strong flashlight and look from the access hatch. You do not need to crawl in to spot standing water.
3. Look for puddles, wet soil, torn plastic and hanging insulation.
4. Listen for dripping and look at pipes for wet spots.
5. If there is standing water, do not go in. Wires and equipment may be wet.

Safety note: crawl spaces can have sharp objects, pests and poor air. If you are not comfortable, have a pro do it.

Start with the simple fixes. Many crawl spaces get much drier just by moving roof water away from the house. For sump pump care, see our Zoeller and Liberty Pumps pages.

Vents open or closed?

Many older Northwest homes have vented crawl spaces. In winter, closing vents can help protect pipes from freezing. Building science on this topic is mixed, so ask a professional what fits your home's setup before making big changes.

Standing water under your home will not dry quickly on its own in our climate. While it sits there, it raises humidity in the whole house and soaks wood and insulation.

Our crews:

1. Pump out the water.
2. Remove soaked insulation and damaged vapor barrier.
3. Dry the joists and subfloor with dehumidifiers and air movers, checking readings daily.
4. Treat mold if needed, and install a new barrier.

We do this across Kirkland and nearby areas, including Rose Hill, Kenmore and Finn Hill.