Basements are always prone to moisture intrusion, which lends themselves to the musty odor. While the finished basement minimizes the intrusion there is no way for the carpet, drywall, etc. to stop that feeling.
Excess moisture gets absorbed by the insulation and carpet and they retain it. This subsequently leads to the earthy or musty smell you are referring to.
A reader asked a question for which I thought of putting out a response post instead of emailing back.
The question was “I have finished my basement, however, it has an earthy/musty smell. The smell gets worse when it rains even though I can’t find any visible signs of water intrusion and I don’t see mold growth either. When I checked for humidity it’s comparable to the rest of the house.
I’m wary of bringing on a contractor to check the issue. Interests might not be aligned and the contractors might jump to the conclusion that the waterproofing needs to be addressed or something similar. Please advise.”
There are several reasons and I’m going to touch on a few that are important. If you’re also having this issue of finished basement smelling musty, then this post is for you.
Inhibit Mold Growth by Maintaining Indoor Humidity
First things first, to inhibit mold growth, you need to have the relative humidity below 50%. The finished basement ends up being tough on the homeowner. In that, even if there is mold growth, that might happen behind the walls and you may not notice.
Mold spores and difficult to remove so try to take all measures to avoid ‘em.
If you don’t have a dehumidifier that is the first thing you must get and put it in the basement. You need to decide on the right spot to place and a perfect location to drain the collected water.
Here is a low-cost DIY dehumidifier idea worth checking.
Ventilation and Move the Air to Reduce Musty Smell
The main problem with many basements in North America is ventilation. Limited windows and poor ventilation make the problem worse. Figure out a way to move the air, which will greatly help reduce the musty order.
Control the Sewer Gas Leakage
Sewer gas can also be causing the musty smell. I know what you are thinking. Sewer smell is distinct and it’s nasty right. You are correct for the most part. Sometimes sewer doesn’t smell like a sewer after all.
Remember to fill the water in all the drain pipes so all the dried P-Traps are filled with water and never let the foul smell come through.
Exterior Water Intrusion
Then comes your water intrusion scenario. You may not able to pinpoint correct where the water is leaking in. But if it is you need to take some measures to keep the water away from the foundation.
Clean your downspouts and gutters periodically. Put in a downspout extender and move the water several feet away from the foundation.
If you have window wells, try to get a good window well cover to keep the water out.
Seal Wall Cracks and the Floor
Since you have a finished basement, checking for wall cracks is going to be difficult.
If you have carpet, then remove and try to clean and seal the concrete underneath. It’s good to check for Radon. While it might not smell musty, it’s better to check for the levels anyhow.
Clean Ducts to Control Mold
You should also consider calling your duct cleaning crew and give it a good nice wipe, so your air quality becomes better. HVAC condensation can be the source of mold growth and the cause of the musty smell.
Now if you have done everything as suggested and still feeling the musty odor, there is a trick you can do to really find out if it’s a one-off issue or not.
Use Desiccant and Absorbent
Get some desiccant or absorbent and keep it in the basement and see the change in effect. Baking soda, cat litter, charcoal combined with some air freshener should remove the smell, at least temporarily.
After a week of this treatment once you remove those items if the issue is gone, then it was a one-off issue. But if the issue reoccur you should dig deep to find the source of moisture.
Ultimately you may end up doing a sound waterproofing, but it may be unnecessary if the issue is small. So, it definitely pays to check and make sure the issue is indeed relatively small.