A client has a house built into a hill, the front of the basement is at grade and the rear is about 6′ below grade.
The floor in the basemtn is concrete with a vinly tile over, I do not beleive there is any inslulation under.
The walls are block, tar paper, strapped with white regid inslulation and drywall.
In the summer the floor in the rooms at the back of the house have a bad condensation problem, that cause mold to develop on the lower exterior walls.
ANy comments or suggestion to remove the problem plese advise.
George
Replies
IF it is condensation the only way to stop it is to lower the relative humidity of the air and/or warm up the area where the condensation is.
The most practical way to do that is to run a dehumidifier.
I would start with getting a humidity guage and checking the temp & humdity in that area, other parts of the basmenet and upstairs.
In some cases just circulating the air (with the lower RH in other parts of the house) is enough to stop it.
If the insulation was installed properly the wall would not be cold enough for condensation unless there is an extremely high RH.
There are a couple of other possibilities. One is that air is getting behing the insulation and condesnsing and draining out and wetting the DW. Another is that water is coming through the wall and wetting the DW.
Another is that there is condensation on the floor and that is wetting the DW.
Thanks for the info
The basement already has a exhaust fan that draws the cold damp air from the floor area , the windows are keeped closed in the basement and by drawing the warm dry air from the first floor has inproved the moisture problem however not completely. A dehumidifer could run 24 hours a day in the summer.
The basement has two issues
The floor most likely has no insulation under and the floor temp. is much cooer then the air. I wonder if installing the 24x24 plywood units with plastic venting under would reduse the condensation problem by decresing the difference in surface temp.??
The second item is the tar paper on the block wall, is it doing more harm then good, should the drywall,and insulation be removed to get at the tar paper to removed it. reinstall the insulation and install blue drywall or maybe even concrete board up 12" from floor??
George
ps. The outside of these walls is well insulated,parged and waterproofed.
Hi Traini;
If the exterior is well sealed as you say, I would create a thermo break between the exterior and the interior. I believe the tar paper IS causing more harm than good. Keep your interior wall (studs & insulation) at least 1" from the exterior. Vapor barrier must be applied on the warm side of the interior wall. You are on the right track with the floor , but their are far to many variables to try to solve that one. Hope this may help!
The basement already has a exhaust fan that draws the cold damp air from the floor area , the windows are keeped closed in the basement and by drawing the warm dry air from the first floor has inproved the moisture problem however not completely. A dehumidifer could run 24 hours a day in the summer.
Do you know, or presume, the first floor air is drier? I'd guess it has the same amount of water in it as the basement does, just warmer, so lower rh.
Don't know where you are as you haven't filled in your profile. We live in a humid climate (Virginia) in an underground house. With a combination of dehumidification and air changes we have no mold problem. There is no insulation next to our buried walls, floor, or ceiling. They are designed to be earth temp. In summer, comprises our passive cooling system. No AC here. Works extremely well, but we're carefully moderating ground temps, unlike your situation.
The latest addition here was a heat pump water heater. In addition to cheap water heating, the byproduct is cool dry air. It reduced our dehumidification needs by 50%. Paid for itself very quickly. It's running (and dehumidifying) as we speak. Now that summer's broken, it's all the dehumidification we need.
PAHS Designer/Builder- Bury it!
Assuming that he is in a humid climate. And that probably covers the southern 3/4 of the country, east of the rockies.He is really paying double using that exhaust van.While he bring down warmer and drier (lower RH, but probably similar absolute moisture) from upstairs he is also drawing in hot humid air from the outside, which the AC needs to dehumidify and cool.Circulating the air within the house will also help bring in the warmer air, but not introduce addition moisture.All of this is assuming that the house is not as well sealed as yours.
Yup. You picture the situation well. Actually, few houses are sealed as well as ours. Concrete's pretty good that way.
Appears he's ignoring our advice.PAHS Designer/Builder- Bury it!
Please fill me in --this home with the problem is in Ontario Canada warm summers (when the condensatin on the floor appears) cold winters. House does not have air conditioning and because it is a summer residents is heated with electrical baseboards in the winter and kept at 6 degrees centigrade.
How would I remove the condensation on the floor any other way other then to reduce the surface tempature of the basement floor in the summer time.( the negative part of insulating the floor would be that the floor is a positive heat gain in the winter?)
Geroge
ps. I do understand that humidity is always present ina home and the humidity will be attrached to the coldest surface.
Dew point is what you want to pay attention to. Requires humidity and a cool enough surface. Change either and you change the dew point. Normally, one changes the easier one, to raise the dew point to a level where condensation doesn't occur.
Humidity isn't attracted to anything, it simply is. When you reach dew point you get condensation.PAHS Designer/Builder- Bury it!
"How would I remove the condensation on the floor any other way other then to reduce the surface tempature of the basement floor in the summer time.( the negative part of insulating the floor would be that the floor is a positive heat gain in the winter?"You mean to INCREASE the surface tempature of the floor.Unless you remove moisture (by condensation) or add it (by boiling water, rain) the amount of moisture is constant. But the maximum amount of moisture that the air can hold is dependent on the tempature. And the ratio between the current amount of moisture and the maximum is expressed as relative humidity.When the tempature is reduced until the RH gets to 100% that means that you will start getting condensation and that tempature is called the Dew Point.That shown by the Psychrometric Chart.http://www.taftan.com/thermodynamics/PSYCHART.HTMhttp://www.arch.hku.hk/~cmhui/teach/65156-7e.htmhttp://www.sp.uconn.edu/~mdarre/NE-127/NewFiles/psychrometric_inset.htmlNow the ground under that slab will be in the range of 50-60 F year around. So it is a heat loss in the winter also.So insulating it will keep the floor warmer winter and summer.
George, I suggest you lay hands on the basement finishing article in FHB #169. Failing that, go to http://www.buildingscience.com to get a handle on the physics of what's going on in that basement.
Andy
Andy Engel
Senior editor, Fine Woodworking magazine
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Thank you Andy wonderful web site.
George
Andy
The article in isuue 169 right on the money,and there it was sitting on my shelf.
George
Why, thank you. I rather liked it, too. <G>Andy Engel
Senior editor, Fine Woodworking magazine
An updated profile is a happy profile.
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
None of this matters in geological time.
Andy in your article you use rigid foam directly over the concrete floor, while at my lumber yard to-day they had a display of a basement floor with a product called Delta Fl. used in the same manner as you used the rigid foam,it is a eggcrate type plastic product that comes on large rolls that takes plywood over allowing air or water to move under the pylwood much like the 2'x2' sections sold at Home depot.
Is your system better because there is no air space between the warm air mass above and the concrete floor below ??
Also this home has a heavy vinyl tile glued down to the concrete would it be best to remove.??
Thank you again for the great article
George
Thanks for the good words.
I'd leave the tile, it's harmless and better there than in a landfill.
I've never used the Delta. I have some reservations because it introduces a vapor barrier which I think would make drying the slab difficult. Also, the foam has a greater r-value. That said, the difference in temperature between the slab and the interior of the basement isn't likely to be huge, so the r-value issue isn't huge, either. And do I really care if there's moisture trapped between the Delta and the slab? Well, maybe a little, given the hysteria over mold these days. Would I worry about it in my own house, given poly below the slab? Not at all.
One thing I can imagine using the Delta for is radon remediation. Since it creates a short plenum under the floor, you might be able to drop a radon vent pipe there.Andy Engel
Senior editor, Fine Woodworking magazine
An updated profile is a happy profile.
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
None of this matters in geological time.
"I've never used the Delta. I have some reservations because it introduces a vapor barrier which I think would make drying the slab difficult. Also, the foam has a greater r-value. That said, the difference in temperature between the slab and the interior of the basement isn't likely to be huge, so the r-value issue isn't huge, either. And do I really care if there's moisture trapped between the Delta and the slab? Well, maybe a little, given the hysteria over mold these days. Would I worry about it in my own house, given poly below the slab? Not at all."What about the tile? That has to be a vapor barrier. So you want have anything coming from below unless you have enough hydrostatic pressure to force water through the joints and then you have a completely different problem.
Yes, the tile probably is a vapor barrier. Somehow that doesn't worry me. Probably because any water under that is likely to stay there. If there's enough water to pass the tile, then it's likely that there's a liqiid water issue that should have precluded the basement from being finished in the first place.
Truth be told, I'm not anywhere as concerned about vapor barriers on the floor as on the wall. Most slabs have a capillary break below them in the form of crushed stone, and there's usually a drainage system of some sort as well. Walls are another matter, frequently being backfilled with whatever waterlogged clay that's laying around. Even though gravity might suggest otherwise, I don't think that most basement floors are subject to the same hydrostatic pressures as are walls, so they're likely to be dryer in the first place. Andy Engel
Senior editor, Fine Woodworking magazine
An updated profile is a happy profile.
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
None of this matters in geological time.
Do you have any idea of the history of slabs and gravel.I finished off a basement for a friend's house.It was orginally a 50's era ranch which had been remodeled once or twice in the 70's and not too well.It appears that the orginal house was very basic, but reasonable well built for the time.I have no idea what, if any, drainage that it had. The lot would have allowed for daylighting. And there where serious problems over the years with water and they later added internal drain system, but never fixed the exterior drainage problems. She had to have the walls braced and after grading the exterior and fixing the gutters and sump pump has not seen a drop of water in 3 years (execpt when I tested it with a hose).Back to the slab.There where clearly places where it was redone putting in the french drain.And the reset of the floor was rough and it looked like it might have been done in irregular sections and/or patched.Anyway it had a "bathroom". The shower was concerete blocks around a floor drain and the toilet was in open space.I had to relocate that and found the slab was only about 2-3" thick and stright over clay (and an old glove that I found).
Yes, I've seen old houses where the slab was right on the dirt. Those are usually pretty apparent to a visual inspection. In fact, I lived in a house where the concrete "slab" was little more than a plaster job. No way would I attempt to finish a basement with that sort of slab. Most of the houses I see have more recent slabs than that. Since the '50s at least, gravel under the slab has been standard practice in most of the country. Since the '80s, so has a poly moisture barrier.
Here's the thing. If a basement has ever seen liquid water, or excessive dampness, there are signs that most of us can quickly pick up. If you see those signs, and you don't know that source of the water has been permanently fixed, you have no business finishing that basement.
Given those caveats, vinyl tile on the floor doesn't bother me. Especially if it's soundly attached. If it's coming up in places, that suggests water entry and merits investigation. Andy Engel
Senior editor, Fine Woodworking magazine
An updated profile is a happy profile.
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
None of this matters in geological time.