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Trapped moisture is home's biggest villain

When the rains start coming down, it’s easy to think of the wet weather outside as an enemy. However, when it comes to your home, it’s actually the moisture that is silently trapped inside that has the worst effect.

In our last blog we talked about what owners can do to prepare their homes for windy weather. In this blog, we’re reminding you about best practices to avoid trapped moisture.

In Grays Harbor, with our tendency to be outdoorsy people, moisture has many ways to get inside our houses. Think – boots, umbrellas, clam gear, hunting jackets – even our pets will carry it inside.

Many normal activities of life, such as cooking, bathing, and doing laundry, create moisture inside our homes. To exacerbate the situation in the fall and winter, we tend to have the windows closed trapping that moisture inside.

It may not seem like a big deal, but over the years in our work here at NeighborWorks of Grays Harbor, trapped moisture is the most damaging issue we see inside homes.

There are the obvious concerns such as mold and mildew, but moisture also impacts much of what you see on the outside of homes too. Peeling paint, curling shingles, rotted skirting and bug damage are all caused or made worse by trapped moisture. They can be prevented by using the correct building materials and methods, properly ventilating the house cavities and timely maintenance.

The good news is that vents can always be installed in your roof, foundation, bath and kitchen, without much expense. After painting, adding vents is the thing we recommend the most often to homeowners in Grays Harbor to protect their homes.

The most typical cause of trapped moisture is still improper and inadequate ventilation.


How do you know if your home is properly ventilated? We thought you’d never ask.

In our area, house attics and foundations should have at least one square foot of ventilation for every 150 square foot of floor area in each of those areas. For example, a 1,200-square-foot house, divided by 150, would need 8 square feet of ventilation in the foundation and an additional 8 in the roof.

This can be achieved by adding 1-square-foot foundation vents at every corner and evenly spaced around the foundation skirt. For the roof, we recommend ridge and soffit venting. Inside the house you should have a powered fan in the kitchen and bathrooms, vented to the outside exterior through metal pipes and flapper vents.By installing these vents you have taken all the preliminary measures needed for a healthy, breathing home.


Today we will focus on the foundation as a source of moisture.

Let’s begin by describing what you want to see and smell under your house.

  • At least one good access point to get under the house.

  • 18 to 24 inches or more space from the ground to the floor joists.

  • Clean, dry 6-millimeter black plastic on the ground, laid tightly, anchored at the edges, cut around each pier block and overlapped at the seams by 12 inches.

  • Very few bugs, spiders or cobwebs.

  • No wood-type debris and nothing growing.

  • All areas of the foundation, especially under the kitchen and bath, should be dry. There should be lots of fresh air streaming through the vents and no odd smells, standing water or signs of animals.

  • All non-treated wood components should be dry, rot-free, away from soil and separated from any concrete by a felt- or composition-roofing barrier.

If you see or smell something you shouldn’t, here’s what you should do:

  • If you see lots of spider webs, that usually indicates a constant source of moisture. Look for leaking pipes and standing water. If you find a water puddle, you need to play detective. Clear water usually means a fresh, constant source. That means you should check your water supply pipes for leaks. If instead it is rainwater, install splash blocks, pipe it or pump it away from the house. Never allow it to go into the city sewer system, though.

  • If it is gray, filmy or soapy water, it means your sink or tub drainpipes are leaking. Operate each fixture, find the problem and repair it.

  • If the air smells or looks like toilet water, stop using the sinks and toilet and call a plumber! That water is hazardous to your health.

  • No pipe leaks, but standing water? Place a splash block at each down spout to convey the rain gutter water away from the house.

  • If there is no plastic ground cover, install 6 mil. black plastic tarp stretch tightly, cut around pier blocks and pinned to the ground

  • Do the formula for ventilation, adding more vents if needed.

  • If you observe any signs left by critters—urine smells, feces, hair, tracks, the critter itself!—trap or remove the animal and secure openings in and under the skirt.

  • Finally, there may be sawdust trails and holes peppering the wood or larger holes, signs of powder-post beetles, ants or termites. You need to get rid of these pests! Depending on the level of damage, a professional pest spray, enough ventilation and removing all sources of moisture will cure the problem. If you wait too long, you may get to replace your foundation, sub-floor and skirting!

If you see considerable indications of moisture damage, you should consider having a professional inspection.

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