# Condensation on ceiling



## Windows on Wash (Aug 30, 2011)

Tear off the roof or tear down the drywall.

What is the roof type (vented or hot style)?


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## packer_rich (Jan 16, 2011)

If the wall is 1 1/2 the normal thickness, make sure there is insulation and vapor barrier. Also make sure there is some ventilation.


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## CooksIn (May 15, 2012)

Not sure what a "hot" roof is, there are vents in the soffit.

Walls are normal 6" walls. Insulation could be some of the problem but would that be in the summer? Winter months it is cooler but no condensation problems on the windows or the ceiling. This happenns only in the summer when it is hot outside.


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## Windows on Wash (Aug 30, 2011)

Think of the warm moist air outside and not the cold roof rafter because you are conditioning the space.

Warm moist + cold = condensation.

Take some pictures but the roof system you are describing rarely works well when it is put together as most folks do.


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## Bob Mariani (Dec 1, 2008)

For a quick solution keep a fan exhausting the moist air out of the room. Keep the humidity under 45% and you will be fine.


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## Windows on Wash (Aug 30, 2011)

Bob Mariani said:


> For a quick solution keep a fan exhausting the moist air out of the room. Keep the humidity under 45% and you will be fine.


+1

Good suggestion Bob.

This will help during the winter months but it will not affect the condensation inside the roof assembly.


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## Bob Mariani (Dec 1, 2008)

Windows on Wash said:


> +1
> 
> Good suggestion Bob.
> 
> This will help during the winter months but it will not affect the condensation inside the roof assembly.


It should only occur in the roof assembly if the ambiant indoor air contains enough moisture and heat to drive (by diffusion) into the assembly and then condense on the surface against the cold roof. In the summer moisture would only be present if the roof is leaking.


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## Windows on Wash (Aug 30, 2011)

Bob Mariani said:


> It should only occur in the roof assembly if the ambiant indoor air contains enough moisture and heat to drive (by diffusion) into the assembly and then condense on the surface against the cold roof. In the summer moisture would only be present if the roof is leaking.


Diffusion and what is more problematic is bulk air transfer and the moisture it carries.

I have seen cold side (i.e. back side of the drywall in the summer) of a roof sweat when the outdoor humidity is high and the space is conditioned and kept cold enough.

This is why most vaulted ceiling assemblies with vented interstitial rafter bays are terrible performers. There ability to resist dew point stinks on both ends of the season.


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## Gary in WA (Mar 11, 2009)

I'm with Bob on this, warm moist air is condensing ON the plastic vapor barrier under the cedar ceiling finish material. Or on the cedar with lack of insulation and well vented rafter bays.

You have an excessive moisture problem. What material is the floor? Is there a crawl-space? Is it vented? Is the dirt covered with a min. 6mil vapor barrier? Is there a v.b. on the ceiling? Are the rafters vented? Is it a slab-on-grade? Is there a v.b. under the slab? Is the backyard always wet- natural springs, valley, etc.? Are you running the AC? Need more info.....

Gary


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## CooksIn (May 15, 2012)

Just failed at trying to load some pictures of the room. I did post them on my FB page if you want to go and look at them.
http://www.facebook.com/media/set/?set=a.3566317910118.2139499.1038013126&type=1&l=b6c3a17826

There is not a slab under the room it is dirt, last fall we closed it with plywood & siding and put insulation on the inside wall. No vapor barrier was laid.

We live on a river, the river is about 300 yards from the back yard. There is some wet land on the property.

The ceiling sweats when the AC is NOT on. If I turn on the AC and the fan it will stay dry. When we first moved in I had no idea what was going on, for that matter still don't. I brought in a ladder and went up to see if I could dry off the ceiling and see if there was a leak or what....At about 8 feet, the air started getting hot, hot and wet and I noticed that the whole ceiling was wet along with the beam. Right now the house smells like hot atic when you come in. When I turn on the AC in about an hour the smell is gone. There is only one register for that room but the register for the oringinal kitchen wall is still there too.

Thanks for all your help on this.

Judy


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## Windows on Wash (Aug 30, 2011)

GBR in WA said:


> I'm with Bob on this, warm moist air is condensing ON the plastic vapor barrier under the cedar ceiling finish material. Or on the cedar with lack of insulation and well vented rafter bays.
> 
> You have an excessive moisture problem. What material is the floor? Is there a crawl-space? Is it vented? Is the dirt covered with a min. 6mil vapor barrier? Is there a v.b. on the ceiling? Are the rafters vented? Is it a slab-on-grade? Is there a v.b. under the slab? Is the backyard always wet- natural springs, valley, etc.? Are you running the AC? Need more info.....
> 
> Gary


+1

That is the most likely and especially given the poster's update. I was just pointing out I have seen both.

Good info though and Bob's original suggestion of the dehumidifier is the quickest way from point A to point B but it is not a long term solution.


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## Gary in WA (Mar 11, 2009)

Sounds like the dirt floor is giving excess moisture which rises from the "stack effect'; http://www.wag-aic.org/1999/WAG_99_baker.pdf
First off, cover the dirt, tape or seal it to the wall mudsill. http://dirt-crawl-spaces.com/crawlspace-dirt.html

If the area is not heated/cooled, ventilate it. Your framing will grow mold and rot if left alone. Is the furnace/HVAC down there?
This may work; http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/

You still need to ventilate (outside air) or move conditioned air down there. Closed crawl: http://www.buildingscience.com/docu...rawl-space-construction-performance-and-codes

Gary


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