basement condensation

nysono · July 28, 2013, 07:07:26 PM

I'm having a very difficult time this year with condensation in my walkout basement. The heat and humidity have been a bear (at least for our area of upstate ny) and I cant keep the basement walls or floor from being wet from condensation. I have tried opening the 4 windows in the basement, closing all windows, using multiple containers of calcium chloride etc......mold is becoming an issue. If we were on grid it would be simple to run a dehumidifier all the time but that is not an option. Water id NOT leaking in. Here is a link to my build if that might help.

http://countryplans.com/smf/index.php?topic=10852.0

Does anyone have any thoughts on fixing this problem
Thanks in advance

Don_P · July 29, 2013, 06:39:18 AM

Heat... unfortunately. If you check the surface temps down there and the relative humidity you'll find that the surfaces are below dew point and just like an ice tea glass sweating the humidity is condensing on those surfaces. If the surfaces are warmed above dew point they will not "sweat". We're growing things too, I've got the wood stove running this morning.

July 29, 2013, 07:28:16 PM

if I stud the walls and place 2 inch foam insulation in the bays and cover will that fix or just hide the problem?

rick91351 · July 29, 2013, 07:48:15 PM

Sounds as if you are only making a problem worse. Mold and mildew will start to grow over time and this can give rise to health concerns. You have to dry it out not cover with a band-aid. You have to move the water that is condensing away from your walls.

MountainDon · July 29, 2013, 08:29:53 PM

IF the moisture is condensation and not water leaking in from the exterior, rigid foam is the answer. It is glued directly to the interior side of the concrete wall in an uninterrupted layer. Or use spray on foam. When a sufficient thickness is used like this the inside of the foam is kept above the dew point and there can be no condensation. The key is sealing it to the concrete wall. It's the same principle used when a roof is insulated with foam and no roof venting is used; also same principle when exterior walls are covered with foam sheet insulation; "keep the interior wall surface temperature above the dew point".

Then frame with 2x4 or 2x3 and sheetrock for fire safety. Use NO fiberglass batts.

LINK for everyone's edification.

... and Joseph Lstiburek has something to say on basement insulation.

More!

July 29, 2013, 10:43:30 PM

Thanks Don I recant my post.....

nysono · July 31, 2013, 05:16:31 AM

Quote from: MountainDon on July 29, 2013, 08:29:53 PM
IF the moisture is condensation and not water leaking in from the exterior, rigid foam is the answer. It is glued directly to the interior side of the concrete wall in an uninterrupted layer. Or use spray on foam. When a sufficient thickness is used like this the inside of the foam is kept above the dew point and there can be no condensation. The key is sealing it to the concrete wall. It's the same principle used when a roof is insulated with foam and no roof venting is used; also same principle when exterior walls are covered with foam sheet insulation; "keep the interior wall surface temperature above the dew point".

Then frame with 2x4 or 2x3 and sheetrock for fire safety. Use NO fiberglass batts.

LINK for everyone's edification.

... and Joseph Lstiburek has something to say on basement insulation.

More!

Thanks for the info Don. Moisture is definately from condensation/sweating. I figures this is the way I would have to go but was hoping for another option. If I insulate walls I will likely have the same problem with the floor I imagine, but maybe to a lesser degree. Also, if I insulate this way will I loose the "no freezing" effect of being underground during the winter months? Temps have been above freezing in the winter months the last two years which makes the water/plumbing situation much easier to take care of while away during that time.

Thanks again for all that have helped during this whole project.
Steve

Don_P · July 31, 2013, 07:28:56 AM

It depends, mostly on the outside temps and how well insulated the above grade sections are. We've only frozen once when unoccupied, at about 10 below but only have a crawlspace. So greater heat losses and less buffer/ground heat gain. You're seeing one reason why I like to insulate under a slab even if it is not a radiant, decouple from the ground temp.

Back to the heat comment, the insulation will help greatly but the relative humidity and dew point are what causes the sweating. We are growing mold/mildew on things like carpet on the floor (insulated floor) and the woodwork of the furniture, doors and cabinets. The humidity is extremely high and our nighttime temperatures that we are trying to capture inside the house are cooling those surfaces below the dew point. Dew points have been in the 60-70 degree range and nighttime lows in the 60's and even 50's recently. That leads to some surface moisture condensing, add a little dust, wool, or even oil finishes for food and mold grows. I just checked readings, 87% relative humidity, 65 degree dew point, 57 degree low this morning = condensation on any surface that cooled below 65. When I worked in cabinets and furniture we tried to keep the shops a few degrees above the average morning lows to avoid picking up moisture. In the summer time it is hard to follow that rule in a warm house. Air conditioning was really first touted as removing that moisture, lowering the RH and preventing mold and mildew (mildew is really just mold on fabrics).

rick91351 · July 31, 2013, 10:15:45 AM

I have been searching for a couple news clips from Boise Schools. One of their newer schools as had health issues tied to condensation in the slab and they have had to replace carpeting - floor covering twice. This last time parents were really causing a worse stink than the rotting carpet.

We never had rotting carpet..... but then we never had carpet.

July 31, 2013, 01:50:44 PM

I think Joe L at building science lists carpet over slabs in schools as one of our less bright ideas

. I think we had that asbestos tile

nysono · August 01, 2013, 05:12:23 AM

We are really only having this problem a few weeks a year. With the high humidity and high temps we have gone through recently and the basement being relatively cool (62-64 degrees) it was a mess. Anything that could feed mold seemed to grow it. Now the temps and humidity have backed off and things are drying out. Has anyone heard/read much about a solar powered dehumidifier? I cant seem to find much.