Moisture at the top plate/wall (Attic)


  #1  
Old 12-02-15, 12:35 PM
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Moisture at the top plate/wall (Attic)

Hello all,

I have a small amount of moisture where the top plate meets the wall in two locations only. The two locations are both drop ceilings for bathrooms. One bathroom never gets used but nether-less there is moisture there. The fiberglass insulation there is slightly wet. Its about R-20 non-faced with a foam baffle (air flow is good), all i can I can do there, never really had any problems until recently. The moisture is obviously happening between the insulation and the top plate.

I was thinking of letting it dry, then spraying a can of spray stuff over the top plate at then putting fiberglass back along with the baffle. I know the proper solution is use a piece of foam with some spray foam but that would be difficult for me to do that.

If I do this am I risking trapping moisture in the wood?, I'm thinking the spray foam would prevent the moisture forming?
 

Last edited by the_tow_guy; 12-03-15 at 04:58 AM. Reason: Typo fixed
  #2  
Old 12-02-15, 01:12 PM
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Going to need far more info.
Tell us about the soffit venting, roof venting, how is the bathroom and dryer vented?
How much insulation is in the attic, has the attic been air sealed?
Been on the roof to check the condition of the shingles and the seals around the vents?
Has ice dams been an issue?
 
  #3  
Old 12-02-15, 01:15 PM
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Hi DBZ
Just a guess, but drop ceilings are often associated with stud cavities open all the way to the floor. Being open, air can leak into those cavities and carry its moisture up until it finds a colder surface (your insulation) where the moisture condenses depositing that water.

Page 70 of the link below gives an explanation.
http://www.efficiencyvermont.com/ste...ide_062507.pdf

Bud
 
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Old 12-02-15, 01:18 PM
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Soffit Venting existing throughout the whole house. All Clear. I have a Maximum Vent 301 on the roof. Bathroom is vented through the roof. Laundry through the side of the house. R60 Cellulose in majority of attic. Yes all major areas plumbing, electrical, vents were sealed. No signs of issues to Roof Sheeting. Shingles in good condition. Installed 3 years ago. No Ice dams. This issue started after I removed the builder fiberglass insulation and replaced it with a thicker insulation batt (its placed all the way in) at the at the wall/roof section. I only noticed it because I wanted to check on attic a year later.
 
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Old 12-02-15, 01:24 PM
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Its possible Bud. I think that's what happening. However, Its only happening on the top plate. I did an experiment and removed the insulation from the top plate. No moisture on top plate or roof sheeting but obviously when it gets very cold, I will have condensation on the roof sheeting as it appears to be heat loss area. So since this appears to be a very limited area, I'm thinking it would be okay to use great stuff spray foam to stop the moisture from even passing but Im not sure if that would cause any further issues.
 
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Old 12-02-15, 01:38 PM
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One vent for a whole roof?
Are the soffit vents clear of insulation?
R-60 is well over 12" of insulation, in most cases baffles would have been needed so the soffits remained clear.
 
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Old 12-02-15, 02:10 PM
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Ya one vent..this is maxi vent capable of venting 1000-1200stft..i have 950sqfoot attic.no problems in last three years..yep baffles are clear of insulation and i can see light.
 
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Old 12-02-15, 02:14 PM
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Maybe I missed it, ranch, 2 story, cape or other? I'm trying to understand the ventilation air flow.
Joe asked about the one vent mentioned, what size is it, NFA?

I can't say yes or no to the can foam as I can not see where you are going to apply it. Also, can foam likes warmer temps.

Heat is not necessarily the source of the moisture. Air leakage is the major transportation mode. Even diffusion through the drywall is usually insufficient to cause a problem if the ventilation is working.

Since you can see the top plate above that drop (a picture would be nice), is there any drywall attached on the inside or an open cavity below?

Bud

You posted while I was fumbling. The maxi vent, is that powered or natural draft? I'll go search.
 

Last edited by Bud9051; 12-02-15 at 02:16 PM. Reason: too slow
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Old 12-02-15, 02:22 PM
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Dont know the nfa but it constantly exchanges the air flow 2-3 times and hour....its one of those tall square chiminey looking vents. 2 story.i would just apply it on the top plate, top side of it but u do make a good point about temps..we are averaging only 5 degree days here.. Will see if i can find an old picture..
 
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Old 12-02-15, 02:31 PM
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Passive venting is a catch 22, it is powered by the warm air it is trying to eliminate. With a lot of insulation, there will be very little heat escaping into the attic and thus very little air flow. Having a higher vent helps, but this may be a case that better insulation has changed the ventilation.

I'm still questioning the source of the moisture. IMO, there has to be an air leakage path somewhere.

Bud
 
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Old 12-02-15, 02:36 PM
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Unfortunately this is the best pictur eI took last year before I re-insulated my attic due to a separate problem. You can see the drop ceiling on the far left.Name:  Untitled.jpg
Views: 667
Size:  37.6 KB

Its a Maximum Vent 301

Product information for the Slope Roof Model #301 Roof Ventilator
 
  #12  
Old 12-02-15, 03:10 PM
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Not familiar with that particular vent, but looks like it should work.

I can't see from the picture how the drop is constructed. As described in that link I provided, often the drop is constructed before the drywall is installed. When you look into the drop do you see the wall insulation and behind that would be the exterior wall.

You mentioned the dryer is vented out through a wall. Is it anywhere near the soffits in relation to the moisture problem. I doubt, but had to ask.

The other common element here is, both areas are bathrooms. Exhaust fans can have condensation issues with the ducts and vents passing through a cold space.

Do you know the humidity level inside your house?

Sorry for all of the questions.

Bud
 
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Old 12-02-15, 03:38 PM
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Hmm...I will see if I can take a look next time I am up there. Its dame near difficult with all that insulation up there and in the drop ceiling. I can say 100% there was fiberglass insulation on the wall side, however behind that insulation there maybe nothing, allowing airflow. What I don't get, this only happened after I removed the builder fiberglass insulation dam with the baffle and put a new higher r-value in its place.

No its vented on the lower level. Bathroom fans are okay and not near the affected areas. Humidity varies, I don't have humidifier on as it hasn't really gotten cold yet, but its currently at 40%.

All good, I appreciate your help trying to figure this out. If I cant figure out the source of the problem, I may put a foam strip or two at the end of the plate if possible with the baffle, plug the gaps and cover the remainder of the top plate with cellulose instead of fiberglass which should at least act as partial seal and prevent the moisture from occurring in the first place.
 
  #14  
Old 12-02-15, 04:06 PM
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Are those drops above a sink. Plumbers often create oversized holes for the sink plumbing, or showers and tubs. Those openings can be the source of moisture making its way into the attic. Another link with a picture near the end.
Find and Seal Air Leaks | Smarter House

Bud
 
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Old 12-03-15, 10:36 AM
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No sink and no plumbing vents directly within that area. I will go up there next week and report if I find anything.
 
 

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