Basement humidity in New Jersey

[greenbaypackersfan]

Hi, I hope this is the correct place to ask about humidity in the basement, since it has something to do or little to do with HVAC and I see no where on the forum where I can post this.

In the winter, the humidity level in my basement is roughly 30~40% , But when it comes to Spring, the level goes up significantly and in summer time, it gets up to 67~70%.

It's Early April and currently the humidity level in my basement is 61% with temp of 68. I have a dehumidifier and I try to set it at 50% last summer. If I do that, the dehumidifier will run too often, so I ended up keeping it steady at about 62%.

Does anyone know what is a good humidity level or % I should be keeping the basement at? It is a finished basement and stays pretty dry. (We are in New Jersey)

(I read many articles that the basement should be kept at 50% or lower in the summer time, but I highly doubt we can do that here in New Jersey. It is a pretty wet state and gets very humid during the summer time.)

thanks

[jadnashua]

40-60% is often listed as the 'comfort zone'. You want it low enough so that you don't get condensation on the walls or floor, and that may require it to be lower, or more insulation added. Any liquid water from condensation will promote mold growth. When you say it ran too long, there really isn't such a thing - they are designed to be able to run continuously (won't help your electric bill, but won't hurt the thing if it needs to - it will increase your comfort level). You will feel more comfortable at a higher temperature if the air is drier.

Make sure that the landscaping around the house is sloped away from the foundation and that the gutters disperse the water a ways away to minimize the vapor pressure of moisture on the outside of the walls getting in. then, if you have access, use some spray foam to seal all the rim joists and any holes to minimize air infiltration.

[Dana]

At 70% and up the mold & rot factor on wood skyrockets. I generally keep my basement down to ~60% at 65% (monitored with a meter, not some cheezy knob setting on a dehumidier) I start to smell mildew in some rooms.

As a summertime-only issue, it's an indication that you have excessive air infitration. Air-sealing the foundation sill, band-joist, and all plumbing & electrical penetrations with spray foam, as well as weather-stripping any hatches/doors/windows can make a significant difference in the duty cycle of the dehumidifier. If your clothes dryer is in the basement, going with a better than average dryer vent to prevent backdrafting & air infiltration helps too.

After you've air-sealed it as best you can, if you have atmospheric-drafted heating appliances (boilers, furnaces, hot-water heaters) in the basement you'll need to check for backdrafting & spillage at the draft hoods when they're when the dryer + kitchen & bath exhaust fans are all running. (If they're power-drafted or sealed-combusion this isn't a concern.) Most houses are hard to make so tight that it's an issue, but if is it, there are solutions to combustion-air supply that don't involve permanent big holes in the pressure-boundary of the building. But open flues from appliances in the basement can be a driver of summertime outdoor air infiltration- a big hole in the pressure boundary that actively sucks (literally), putting the basement at a slightly lower pressure than the outdoors. Plumbing chases with vent-stacks running from basement to attic & above can be too but those you can (and should) be foam-sealed whereas you're pretty much stuck with atmospheric-drafted burning appliances and open flues.

Ground moisture can be a significant secondary source, and concrete sealers (even vapor-permeable sealers) can cut that factor in half. In new construction it's best to put a poly vapor retarder under the slab. Foundation walls should only be sealed with vapor-permeable sealers or the humidity of the concrete can rise to the point where it rots your foundation sill.

If you go ahead & foam seal the foundation sill & band joist, you might as well have a pro do it to insulating, not just sealing levels of 2" of closed cell foam, or 3" of open cell, (NJ has rebate programs for that sort of thing.) The reduction in air infiltration is large, but so is the reduction in conducted heat loss in this oft-neglected place. Avoid using fiber insulation to insulate that area, since interior air can pass through and condense on the wood all winter- it has to be and air-tight insulation, and by the time you've put 1/2" of spray foam up there, you might as well finish it. (Some people cut & cobble rigid foam board and seal it with 1-part foam, but that can add up to a lot of hours in some houses.)

[greenbaypackersfan]

Great infos. Thanks to both of you. The basement is already finished and I would think it is hard to spray foam all the sills and joints now ? The house was built in 2003 and we moved in here last May (2009). It was about 85 degrees today, pretty humid and the basement humidity was at 59%. When AC kicked in, the basement has a humidity stat and it rises to about 63%, there are 2 vents here in the basement but no return... perhaps that is why?
It is hard to keep the humidity level below 60% here in NJ unless I constantly run the dehumidifier or install a whole-house-dehumidifer.....
the basement does not smell damp or feel damp, just looking at the humidity stat that says 63% bothers me hehehe.... I know this humidity stat tells me the comfort level (at 44% - DRY) (45~65% comfort) (66% and up WET) that what it says

[jadnashua]

Cooler air can't hold as much moisture, so it is to be expected that it would go up as the temperature goes down. See if you can add a return to that room, and it will benefit from the inherent dehumidification that the a/c provides.

[njplumber]

If you are still having a problem w/ a wet basement (and the dehumidifier didn't help) you might want to call in the pro's...there's moisture lurking somewhere in there, and you'll need to get it out before mold starts growing.

If you aren't sure who to call, give us a try! 888-460-2371 (or on the web at http://plumbernj.net)