Trapped moisture is an invisible enemy to your house


When it comes to your house, it’s something that is hidden that can typically do the most harm.


Trapped moisture. It is your home’s greatest enemy!!


During wet fall and winter months, especially, it’s important to stay on the alert for sources of excessive moisture.


We’re not just talking about a leaking pipe, which of course is also a source and obvious concern. Instead, we are talking about the sneaky type of moisture that comes from wet jackets and shoes, cooking, showering, wet pets, watering house plants, other house leaks and more.


As those sources of moisture evaporate into the warm indoor air, they linger through the house until they find a cool wall surface, toilet tank, or even a thermal pane window to turn back into a liquid state. We are sure you have seen it happen!


When this water vapor finds these cool lower corners of rooms, bottom walls of closets and certainly anywhere in an unvented bathroom, it sticks and stays, creating a little environment for black mold and mildew. None of this is good for you and it can be pre-vented – literally.


Over the years working for NeighborWorks of Grays Harbor, we have inspected and directed the rehabilitation of hundreds of moisture-damaged homes. From the foundation to the roof, improper ventilation in one or more areas is usually the problem.


Moisture damages houses!

You may assume much of what you see in and around homes is just normal wear and tear. However, things like peeling paint, curling shingles, rotted skirting, mold, mildew and bug damage are not normal and can be prevented with proper ventilation and timely maintenance.

As we said, it’s not just our rainy weather that’s hard on a house, these other moisture sources– even breathing – all contribute to a potentially high humidity problem that can cause real trouble.


The good news is that specific vents can be installed in your roof, foundation, bath and kitchen to take care of the excess moisture.


Defining adequate ventilation

So, how do you know if your house is adequately ventilated?


Homes in our area should have one square foot of ventilation for every 150 square foot of foundation floor area. Same for the attic using roof vents. For example, a one-floor 1,200-square-foot house, divided by 150, would need 8 square feet of ventilation around the perimeter of the foundation and again in the roof.


This can be achieved by adding 1- square-foot foundation vents at every corner and evenly spaced around the foundation or skirting. For the roof, we recommend ridge and soffit venting, but there are other ways to get the job done.


Inside the house you should have a powered fan in the kitchen and each bathroom that is properly vented to the outside. While openable windows can help, they are not as efficient and, of course, only work if opened.


By installing these vents, you have taken some of the preliminary measures needed for a healthy, home and you.


Is foundation wet?

Let’s focus deeper attention on just one area—the foundation—as a forgotten source of moisture.


Here’s what you want to see and smell under your house:

  • At least one good, screened or covered access point to get under the house.

  • 18 to 24 inches or more of 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 using composition roofing or other water-proof barrier.

Ick! What now?

This is what you should do if you see or smell something you shouldn’t:


If you see lots of spider webs, that usually indicates high moisture content in the air and may indicate you need more ventilation and/or a ground cover. Installing 6-mil black plastic on the ground under the house stops this moisture source, instantly.


Next, place a splash block or a pipe at each downspout to convey water away from the foundation

Now do the math for ventilation, adding more vents if needed.


If you find a water puddle on the plastic ground cover, you need to play detective. If it is gray, filmy or soapy water, it means a sink, tub or washing machine drainpipe could be leaking. Operate each fixture, to find the leak point and repair it.


If the air smells or looks like toilet water, call a plumber! That water is hazardous to your health!


A puddle of clear water on the plastic can be from rain through a vent or a water supply line drip. We would first look at the water meter ‘tattle-tale’ and see if there is a leak indicated. If not, look for another source and the reason why, like rainwater.


You may have to install splash blocks under downspouts to pipe it away. If you have a lot of ground water you may need a sump pump to carry it away from the house but avoid sending ground water into the city sewer system. That’s a big no no!


Dealing with other issues

If you observe any signs left behind by critters—cat pee (smells like ammonia), feces, hair, tracks, or even the critter itself—trap or remove the animal and secure openings and under the edges of the skirt.


Finally, there may be small sawdust trails and holes peppering the wood, signs of powder-post beetles, or larger holes that ants or termites make. Poor ventilation and/or a steady source of moisture on wood can create a condition known to attract pests. Bottom line is you need to get rid of these pests and the moisture sources that allow them to be there! That may require the knowledge and products professionals use.


Depending on the level of damage, a professional pest spray, proper ventilation and removing all sources of moisture could cure the problem. If you wait too long, you’ll have to replace your foundation, sub-floor and skirting.


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