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How to Identify Moisture Problems in Your Basement

Monday, September 14th, 2015 by Ben Kershner


"My Basement's Not Wet!"

This basement wall is OBVIOUSLY wet.My wife and I bought our first house this spring.  It has a large dry-looking  basement that could someday be converted to living space.  The building inspector agreed that it looked dry.

Unfortunately, there’s a big difference between a basement that LOOKS dry and a basement that IS dry.  We had an old dehumidifier that was happily “chugging along” in the basement making dehumidifier noise, but when I got out the gauges, and took some readings, I found that I had a humid basement.  What could be wrong?

How could this have happened to someone like me!?

First, let’s track down the sources of moisture in a typical basement. 

Standing water in the sump crock evaporates out into the air.  Many people have their dehumidifier right next to the sump, so that the water from the dehumidifier runs down into the crock, then evaporates and goes right back into the dehumidifier.  Let’s take the load off the dehumidifier and put a cover on the sump crock.

Next up, the clothes dryer should be properly vented.  If your dryer vent is leaky, you’ve pumping tons of water into your basement.  How do you know if your dryer vent is leaky?  How much lint is stuck to the wall behind your dryer?  Where’d that come from, anyway?  While we’re on the topic of dryer vents, if you’ve got a gas dryer, make sure you’re venting it with a pipe that’s safe for gas.  Flexible or corrugated hoses should not be used for gas dryers.  This is a serious fire-hazard.  OK -- back to water-sources.

Check your water heater for melted caps.  This could be a sign that your water heater is “backdrafting” or “spilling fumes.”  In other words, the flue-gasses from your heater are not going up the flue-pipe as they should, but are instead being sucked back in to the basement.  (The smoke’s not goin’ up the chimney!)  This is a problem both because of the massive amounts of humidity in those fumes, but also because of toxic chemicals such as carbon monoxide.  One of the primary byproducts of burning natural gas is WATER in the form of steam, and it USUALLY goes up your chimney and away.  Make sure your furnace and water heater are drafting properly so that the exhaust isn’t in your basement.

In the summertime, a drafty basement, or a basement with the windows open, will pull in the warm humid outside air.  Basements are usually dark and cool places.  That warm humid air cools down quickly when it’s underneath your house.  Because cool air can’t hold as much water as warm air, you get rising humidity levels, and sometimes condensation.  Keep those basement windows closed in the summertime – it’s humid out.  Keep them closed in the wintertime too – it’s cold out.  Even if your basement windows are closed, if your rim joists aren’t sealed, you’re letting in a lot of air.

Water in this brick basement wall is causing the paint to peel off, and the brick to crumble.How about the walls themselves?  I’ve seen foundations made of cinderblock, poured concrete, brick, fieldstone, and more.  All of them are porous, and all of them can absorb, hold, and release moisture into your home.  How do you know if your basement walls are secretly wet?  Look for peeling paint, for dark and light patches, and for “efflorescence.”  When stalactites form in a cave, it’s from water picking up minerals above the cave, and depositing them as they drip… drip… drip… off the stalactite.  Efflorescence is the mineral deposit left behind by evaporating water in this basement wall.The same process pulls minerals out from your foundation and deposits them on the surface as the water evaporates.  It can look a little bit like mold, and a bit like salt stuck to your wall.

Next, let’s look at the floor.  Concrete?  Dirt?  Gravel?  Sand?  I hope your answer was concrete, but even then, we can have humidity problems.  Without hesitation, you need to seal your dirt-floor crawlspace or basement.  The same goes for sand, gravel, or any porous material.  The ground is full of water, and it evaporates up into your home.  Often times, the floor will LOOK dry because all the moisture in it is evaporating up into your air!  Does your concrete slab look dry?  Grab a sheet of thin plastic, like a large trash-bag or a dry-cleaner’s bag.  Smooth it out on the basement floor, and tape down the edges.  After a couple of days, come back and pull it up.  Is there a wet patch underneath it?  Even well-sealed basements can absorb humidity through the floor. 

If you have a dirt-floor crawlspace attached to your basement, that little piece of plywood isn’t keeping the crawl’s moisture out of your basement.

Check your landscaping and gutters.  Water from your gutters should discharge at least 5 feet from your foundation – and if your gutters are full of maple seedlings, then they’re not working properly!

So – back to my house.  I had most of these problems above.  Some, I knew about before I bought the house, and others I didn’t.  But don’t worry – I’m getting it all fixed.  And that little dehumidifier happily making noise in the corner of the basement – turns out it wasn’t doing anything at all.  A brand new high-efficiency dehumidifier did the trick (and was quieter and cheaper to run, too).

So:  Now I can have a dry basement. 

Next misconception I need to challenge: My hair’s not going grey!

About the author

Ben Kershner

Ben Kershner is a home energy advisor at True Energy Solutions, and is a regular contributor to our website. He lives with his wife and family in Greece, NY.

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