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Dripping condensation on ceiling during cold weather - cause and remedy?

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  #1  
Old 12-04-13, 06:44 PM
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Dripping condensation on ceiling during cold weather - cause and remedy?

During cold weather under 35 degrees, we are having a problem with condensation forming on the ceiling in areas near the outside walls. It occurs in a bedroom with the door open, a bedroom with the door closed most of the time, and in the living and dining areas.

There are temperature differences in all rooms so too cold or too warm doesn't seem to be the issue.

I first thought that it could be thin insulation in the attic in spots but since it seems to occur in specific areas of the ceiling near the outside walls and not along the entire wall I may have come across a common theme.

There are soffit vents in the eaves in the same areas that I am having the dripping ceiling condensation. Could this be the problem?
If so, would covering these soffit vents in the winter help?
Would covering the soffit vents cause other problems?

This has been a concern for several season. Our house is not overly warm, thermostat is set at 68. The house is fairly tight (no drafts).

Your thoughts are appreciated.
 
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  #2  
Old 12-04-13, 06:59 PM
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This could be a lot of different things.
First thing I would look at it the roof to see what type venting there is and if there was enough of it.
Last thing you want to do is block the soffit vents.
Having bathroom vents and running them even after a shower is taken.
If you have gas non vented heaters running crack a window open. They put out a lot of moisture.
Air sealing the attic.
In your area there should be R-50 insulation in that attic which is about 12". What's up there now?
Having a vapor barrier on the ground under the house if there's a crawlspace.
If there's snow on the roof now and there's below freezing nights and there's no Ice and water shield on the lower edges of the roof water will work it's way up under the shingles and may leak in the outside walls.
 
  #3  
Old 12-04-13, 07:39 PM
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Heatwise, we have a traditional vented gas furnace.
In '98 we had new triple pane windows installed and blown-in insulation into the attic, I would have to doublecheck but the attic insulation may be R38.

The house is an early 60s split level built on a concrete slab.

There is no snow on the ground or roof and it has been sunny and dry, 35-40 during the day and 25-35 at night.

I am still curious about the relationship between the soffit vent locations are the same locations of the ceiling sweating. The eave soffit vents are about 12" x 15".
 
  #4  
Old 12-04-13, 08:45 PM
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The sweating you have, is this moisture forming on the inside surface or moisture dripping onto the ceiling from the attic above?

If it is the inside surface, then excess humidity is forming condensation on the coldest areas of the ceiling and that would correspond to the outside perimeter and vent areas. But, as joe stated, you certainly do not want to close off any attic vents. Less venting may result in condensation and mold in the attic.

When they added insulation to the attic, they should have installed wind baffles to prevent the cold incoming air from filtering through the insulation and maintain a air path for venting into the attic. Lacking baffles that lip over the outer edge of the ceiling will result in cold spots where the vents are.

Joe is looking for extra moisture. One other source can be backdrafting of the gas furnace or water heater. This would not only dump a lot of moisture into the home, but add the risk of carbon monoxide. Do you have a whole house fan?

Is the dryer vented to the outside.

Do you have a humidity gauge to give us some numbers?

Bud
 
  #5  
Old 12-04-13, 09:19 PM
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The moisture is forming on the inside surface of the ceiling and dripping (if we do not wipe it) to the floor. Or in the case of my daughters room dripping from the ceiling to the floor and from the ceiling down one wall. She keeps her door closed pretty much 24/7 and her room stays cold.

I am not familiar with wind baffles but I would say there are none.

I do not have a whole house fan. I assume you are referring to a fan that exhausts from the house? If that is the case, I only have a bathroom fan and range hood (very weak) that exhausts through the roof.

I would say the venting for the gas hot water tank and furnace is fine as the hwt was just replaced and the furnace just a few years ago. I also have a carbon monoxide detector although it is not in the garage where the hwt and furnace is.

The dryer is in the basement and vents outside.

Humidity in the kitchen/dining area is 39%.

I have put the "weather station" into my daughter's room (opposite end of house) to see what the humidity is in there.... and after 10 minutes, it has gone up to 41% so far.

I have a partial floor built in the attic for storage... don't know if that is valuable info or not.
 
  #6  
Old 12-05-13, 04:31 AM
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Here is an illustration of a baffle to prevent wind washing. Top of page 4 here: http://www.dca.ga.gov/development/co...gKeyPoints.pdf

Here is a dew point calculator to illustrate how that 40% RH can turn to water drops on the ceiling. Temperature, Dewpoint, and Relative Humidity Calculator

With a house temperature of 68 and a RH of 40% the dew point is 43. The surface temp of those problem areas would need to drop to 43 to cause a problem. If that is what is happening, then the problem is clearly the need for better insulation (or installation) in the attic. In addition, I would expect some air leakage paths, maybe not all the way into the house, but from the outside into those problem areas. Being a 60's home, there may be board sheathing (lots of gaps) on the outside, or in some cases just strapping, which allows a lot of air infiltration into the walls. What do you know about the construction of the house and insulation in the walls?

Use your hand to check the surface temperatures where the condensation is forming. It should feel quite cold is this is the right line of thinking.

Bud
 
  #7  
Old 12-05-13, 05:14 AM
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RH in my daughter's was up to 47% before I went to bed last night.

Regarding construction, the exterior is the original painted 3/4 cedar horizontal lap siding.

Regarding insulation in the walls, I am not sure.

Yes, the areas of condensation feel colder and damp.
 
  #8  
Old 12-05-13, 05:25 AM
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Just another guess, blown in insulation to get an R-38 would be about 12" thick.
If you laid boards over the joist for storage and compressed the insulation it's no longer R-38 and will tend to transfer the cold air to the ceiling below.
 
  #9  
Old 12-05-13, 08:52 AM
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A temporary solution would be modifying your living habits to minimize the RH inside the home. Or, pick up a good dehumidifier. Some areas of WA are noted for high humidity levels, so opening a window a bit may not work for you. But getting the inside RH down below 35% would be a start. Note, that is 35% at 70 F. If you measure the RH in a colder room it will read higher even though it has the same moisture content.

Here are some typical suggestions: Shorter showers, run the exhaust fan for 20 minutes after showers, don't dry cloths inside, less cooking (your wife may like that), and limit any other activity that generates moisture.

As for the cold, look at any exposed exterior wall areas or the roof, maybe the garage, and see if the house is covered with boards rather than plywood. If boards, you will notice the gap between them. No easy fix unless you are replacing the siding, probably not on your list. If they had actively air sealed before the new insulation was installed it would have helped.

The quick approach would be to bring in a good energy auditor with a blower door and infrared camera. Even though it would cost a little, they would point you directly towards the problem areas and proper solutions. The fixes would easily save more than the audit cost.

Bud
 
  #10  
Old 12-05-13, 11:47 AM
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Floor in attic is 7/16" OSB. Existing 2x6 (2x8?) ceiling joists have a 2x4 on top of them for added insulation height. Raised floor does not extent to the exterior walls below.

I know the range hood is a very weak one Nutone and I want to replace it with a much higher cfm hood. My wife does cook regularing and that would help I would think.

One daughter does take career showers so I can talk to her about taking shorter ones and we can leave the fan on longer.

Humidity level in daughters room is now 50%.

Actively air sealed? We only had insulation added in the attic when we have new windows installed.

Perhaps the house is just too tight.

How do I query an energy auditor and what do I specifically ask for?

Any suggestions for a good portable (and quiet) dehumidifier?
 
  #11  
Old 12-05-13, 12:11 PM
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Tight is a difficult state to determine. Unless it was aggressively built to be tight, almost none are, then it would qualify for "not being leaky". But, even that good a house will still exchange all of its inside air every 3 hours. When they get them tighter than that you need to add a source of ventilation, often a heat recovery ventilator. But a 60s era split level is not going to be too tight, energy was way too inexpensive back then for them to even consider the extra effort. And once built, you can never (almost) get back to really tight. In your case winter air infiltration is probably good, depending upon where in WA you are located.

Careful with a more powerful exhaust hood. when time we can discuss.

Home performance Washington (a dot org) can get you started selecting an auditor:
Home Performance Washington - Certification I know a couple but can't promote their business on this forum, but WA is very active in energy performance.

If Airman will chime in, he knows the dehumidifier selection the best.

Bud
 
  #12  
Old 12-05-13, 03:52 PM
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If the blown-in was fiberglass, the soffits are wind-washing it to reduce the height/R-value there. And the wind coming in is cold further dropping the temp of the top plates/ceiling around them (wood is R-1.25 per inch). You may not have a balanced system where your soffits are undersized/too far apart. They should be continuous or at least vent each rafter bay otherwise more volume will be supplied = more wind-wash to make-up for non-vented bays. In early '70's I framed houses with R-9-11 in the walls; both low density insulation inherent with convective loops even with a "good" install. The room heat is deposited on the top outside wall face, under the double top plates; pp. 45-47- http://www.buildingscienceconsulting...Measure_Up.pdf

The excess moisture from a person in the room is condensing on the colder ceiling near the exterior wall/soffit vent; The "first condensing surface" due to lack of insulation there- BSI-049: Confusion About Diffusion — Building Science Information

IMO, check for proper vent ratios; Air Vent: Continuous Soffit Vents Specifications Proper soffit vents,
 
  #13  
Old 12-06-13, 08:39 AM
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I contacted one of the auditors I know in Washington and he suggested you contact the "Washington State University Extension's Energy Program" and see if they have reference program.

FYI
Bud
 
  #14  
Old 12-09-13, 06:04 PM
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I was away for a couple days. I managed to control it some by leaving my daughters bedroom door open and leaving her ceiling fan on. Currently in her room, humidity is 38% I saw it as low as 22% a couple days ago. Humidity must rise quickly when the door is closed and the fan off.

In the living room it is 68 degrees with a humidity of 45%.

The temps outside are moderating as it begins to warm up. Currently the numbers are 32 degrees and a rh of 61%.

The wet spots are not dripping anymore.

Regarding the soffit vents, there are two per side of house, each measuring around 12" x 15". That would fall in line with Gary's thought.

Bud, thank you for the suggestions. I will follow up on that. Although off topic, I am curious of your comment earlier in this thread regarding being careful about a more powerful range hood. The current big box cheapie hood that we have isn't really doing the job.

All in all, the problem will moderate even more as the temps reach into the 40s by mid week but I do need to follow up on this.
 
  #15  
Old 12-09-13, 06:51 PM
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They really got carried away with range hoods with as high as 1,200 CFM. Problem is they will depressurize the house enough that all natural draft appliances (furnace/boiler and hot water) will backdraft all exhaust into the house. Even a 400 CFM can cause problems. Energy auditors will run what we call a CAZ (combustion Air Zone) test where we establish the worst case condition, all exhaust appliances running, and then measure the pressure to determine if all appliances will draft properly. Another good reason to know a friendly energy auditor as few HVAC contractors perform this test.

Whole house fans present the same problem.

Bud
 
  #16  
Old 12-13-13, 12:05 PM
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If you have a natural draft water heater, go and check if you see any melting of plastic. See my attached picture.

I only have one exhaust fan in the whole house (kitchen) that pulls about 30cfm. However, I do have a whole house fan that we used a lot during summer. During a CAZ test that I had performed, with the whole house fan at its highest speed, the house was depressurized almost as much as the blower door (50 Pascals) and the water heater flue showed significant backdrafting as well as carbon monoxide leakage.
 
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