Venting Crawl Spaces in the Maritime Northwest

If you have a vented crawl space, and you live in the maritime Northwest, you do not want to even THINK about closing those vents in the winter.

If I ask the average homeowner which season, winter or summer, will moisture levels be generally higher in their vented crawl space, most will say, Winter.

This is logical and obvious.

It is however, not true.

We actually have to vent our crawl spaces in the wet cold winter in order to lower humidity levels that have built up during the summer.

I know this sounds crazy, but that is the crazy thing about science---it functions by physics, not thinking.

I set up a little demonstration with how this works.

Let’s pretend for a moment my car is my crawl space.  Now the temperatures would not be the same but the same principles would apply.

As you can see, the windshield is all fogged over and the temperature is 66 degrees F and the humidity is almost 73%---I am obviously full of a lot of wet hot air to fog up my windshield.

Watch what happens to the humidity as I open the window and let all that wet cold air into the car.

The humidity lowers to 62.6%, the windshield clears, and the temperature barely changes at all.  (The fact that it is a hair higher is just an indication the first pictures temp was probably slightly low.)

This next picture shows the actual outdoor temperature and humidity.  We took 57 degree air at almost 81% humidity and lowered the humidity inside the car.

This is the magic of science.

If anyone tells you, you should block your crawl space vents in the winter (and you live in the Maritime Northwest) to prevent all that wet air from getting into the crawl space, tell them they have no clue what they are talking about.

Charles Buell, Real Estate Inspections in Seattle