Basement Humidity

gene_2007

17 years ago

The quick question - Should I / Can I add a return duct to the basement in order to reduce humidity in the basement?

The details -

I have a "finished" basement. It doesn't feel like one since it was done in the early '60s with panelling and other out dated materials. Some areas of the basement are not finished (eg. exposed foundation), like the laundry room and a closet.

The basement is very humid - at least it is now in the summer. I haven't checked it in the winter. My dehumidifier is filling to capacity and shutting off at least once a day. I empty it before work and when I get home, it is full. When the dehumidifier was not running for a few days, the humidity was 80%. When it is running, the lowest I can get it is about 65%.

One thing I'm surprised about is that I can't find any condensation anywhere. I checked the concrete walls, panelling and the cold water pipes. Nothing.

I am about to remodel my basement and am afraid that excessive humidity will ruin it, although I don't seem to have any problems now (other than the humidity itself). There is no mold or odors.

The basement living area has the laundry room adjoining. The laundry room also contains the furnace and gas hot water heater. The door to this room is always open, so perhaps this is where much of the humidy is coming from? There are two washers and two dryers. Yes, the dryers exhaust to the outside. When I remodel, I plan on putting in a door and keeping it shut.

There is no A/C in the basement - don't need it. There is heat, but not from the furnace. It is actually connected to a heating system from another part of the house. The basement has hot water baseboard.

My furnace has a return run that runs across the basement and through the foundation to the outside. Some people told me this is good because it provides fresh air to the house; others say this is bad because the furnace has to heat freezing air.

Finally, my questions -

1) Keep the return duct to the outside or close it off?

2) Add a return to the basement living area?

3) Why is the humidy so high in my basement?

4) Will adding a return in the basement help with the humidy?

5) Will painting Drylock on the walls help with the humidy?

6) Are there other alternatives to help with the humidy? Should I get another dehumidifier?

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Comments (4)

fnmroberts
17 years ago
Others will most likely chime in, but I'll give my thoughts to your questions.

1 - Probably not. The "return" duct to outside is most likely combustion air. Keep it. By doing so, you are not burning already heated air when the furnace is running which then has t be replenished via air infiltration through windows and doors (only to be heated). Also, the outdoor air will have a slightly higher oxygen content to make the furnace more efficient.

2 - Yes. Because cold air settles, the basement will be cooler summer and winter. Cooler air has a higher humidity content. By recirculating it you will dehumidify as it passes the air conditioning coils and actually circulate the cooler air through the house. If the humidity is still high in the summer a dehumidifier may still be necessary.

3 - See "2"

4 - Yes, see "2"

5 - I believe it will help, but most of the humidity is most likely passing through the concrete from outdoors. Concrete is porous. Newer homes have a rubberized moisture barrier sprayed on the exterior of the foundation before backfill. Yours most likely does not. I would speak with a qualified paint supplier to see if Drylock or another paint will help.

6 - When you redo the basement, I would consider rigid insulation and possibly a plastic moisture barrier across the studs. Consider pressure treated lumber for the studs since you know there is a high moisture content in the space.

Hope this helps.
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gene_2007
Original Author
17 years ago
Thanks, fnmroberts. This was very helpful. Regarding #5, Drylock, I was talking about putting it on the foundation walls (inside, of course). Like you said, I think most of the humidity is coming through the foundation, so that is why I was wondering if Drylock would help.
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I have used several different makes and models of dehumidifiers. Most of them were noisy and several were short lived-- less than 2 years. My most recent purchase is the Frigidaire FAD740DUD. Much quieter than any other I have owned and apparently much more efficient as it keeps the humidity level as set with much less running. Cost about $240 delivered to my house. If your situation was in my house, I would buy one of the Frigidaire to try and then if I was pleased with it, buy additional units to place in other parts of the basement. I have two dehumidifiers in my basement. Not sure if it will be significant on my power bill, but the sharply reduced running time should help reduce the running cost. I think my old unit was just not doing much moisture removal at the last. This post was edited by bus_driver on Sat, Jun 8, 13 at 12:19
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The dehumidifier should be sized so that it will not have to run full time. No humidifier will last long at that pace; the coils can actually freeze up. It's hard to imagine how a dehumidifier could be too big. Moisture can enter the basement from humid bathroom air or from humid outside air and it usually condenses against the cool concrete walls. Also, inadequate waterproofing on the outside of the walls can allow water to slowly enter through the wall and this can be exacerbated by not enough slope to the grade at the perimeter of the house and the absence of a footing drain. The absence of an adequate vapor retarder membrane under the floor slab can also add to the moisture problem. The fact that the window wells filled up indicates a failure to provide a drain at that location. See if that was included in your contract but omitted. You need to assume all of these issues are problems and then try to eliminate them one at a time. First, get the downspout terminations and surface drainage to run away from the house. Then put a piece of plastic on the concrete slab and tape the edges with duct tape. If moisture gets trapped under the plastic after a few days, the builder probably omitted the code required vapor retarder membrane under the slab. He might also have used a damp sand bed under the slab and that can take a long time to dry. What does the sump pump serve? Is there a perimeter drain? Is it outside or inside? Find out what the exterior wall waterproofing was and what kind of drainage/protection/insulation board (if any) was put over it. Your contractor is obligated under the warranty to do all of this for you since the moisture is excessive but he will probably drag his feet and blame issues beyond his control. If you can't push him, you might might have to get out in front and figure it out yourself. A local home inspector can be helpful.
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I will give you my honest opinion on this. I believe it is definitely a climate issue. If they originally took moisture readings, I truly believe you have professionals in your home. The way the sub floor is running will not be relevant as they screwed to your joists and through the existing sub strate. Screws will not be of issue and no reason or relevance to a suit unless you prove it is causing a problem which you can't. I believe it is definitely climate driven. Proof to it is that it takes time, then it shows up as the RH and moisture levels go high. If wood gets wet it will swell causing the seams to telegraph. It at times is impossible to figure the cause. Humidity levels must stay fairly constant between the basement and the living area. Now this store came to your home and reinstalled, testing moisture. They reinstalled to eliminate doubt that Patch was defective or that acclimation was not proper. They reinstalled and after time, it swells again. it is moisture. Unless the climate in your home stabilizes, it will continue. One way to eliminate the issue and I would talk to them about it, is a high end loose laid vinyl. The moisture will not matter as when the underlayment swells, it will not be noticeable. My store has resolved several issues in this way as we knew it was not an installation issue. There is no way the store can possibly know what happens when your climate changes in the home. 15 plus percent at the joists is high.. It is wet. Things swell when they get wet. You may never get an environment that works. Sometimes it requires a 60 Degree temperature maintained in the basement. Or a landscaping change, or may other variables that can cause underlayment trouble. 16% Moisture is up there. Look to a floating vinyl. Talk to them and see what can be done. Move away from trying to fry them and come up with a resolution together as they replaced it once, the sound very professional and want you happy. You must bring a proactive attitude to the table. If you act like their enemy, that is what you will be. Work through this together and they will help you get it resolved. Remember, if it is climate change in your home, they are not God to know this and it will not be their fault and you can't throw stuff at them that has nothing to do with why the problem is happening. It is moisture, not the way the flooring is run. If their is not a void in the plywood which it would feel like a hole if their is, the ding will be consumer's responsibility. Work with them. let us know how you make out.
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Boy can I relate to the 60's wood paneling. I'm in the same boat right now. For heat, how about electric baseboard heaters? They are inexpensive and easy to install. Once you have the right insulation installed, it won't take much to keep the space comfortable. The plus side of the separate zone of electric is that you only need to use it when you are down there, and being warm in the basement won't be a function of the upstairs calling for heat. For a basement, the cooling load is likely to be so small as to make the installation of cooling ducts unnecessary, unless you have large windows that get lots of sun. As far as a return for dehumidification purposes, is the basement space going to be continually open to the condition space above, or will there be a door to close it off? If you tap into the forced air system, the supply registers for the heat should be located low on the wall down near the floor. The returns should also be near the floor, preferably on the opposite wall. You want them situated like this so that there is a good circulation of air, something that is essential to proper function in a forced air system.
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fnmroberts
17 years ago
Yes, I understand. Not being familiar with the product, I would rather suggest that you speak with a qualified retailer because of the possibility that moisture trapped within the foundation walls might cause it to pop. Better to be informed than disappointed.

Photos of our finished basement are linked from "My Page". Captions accompany many imaages. Might be some ideas for your new space.

Good luck.
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bus_driver
17 years ago
I have two dehumidifiers in my basement, each separately controlled by a wall-mounted Honeywell humidistat set at 50%. They ran a lot for about the first year. Now they just run occasionally. By experimenting, I discovered that mildew (fungus) may grow at 60%, certainly will at 70% or higher relative humidity. Rusting of steel also is greater at humidity levels above 50%. If the basement is cooler than outside temperature, and that is virtually certain in the Summer, the relative humidity in the basement will be higher than outside.
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Basement Humidity

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gene_2007
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