Why is the interior of our exterior sheathing wet?
Renovation on master bath, took drywall off, then vapor barrier and insulation, house is a very well built ( we built it) 30 yr old home, two story, and noticed inside of exterior sheeting wet? Also whether related or not, have had dark dirty water migrating down outside of vinyl siding, in area of this bathroom. Just had siding replaced 5 yrs ago from aluminum siding. Had typar placed as well, have had many contractors look, seems many suggestions, but no solid reasons why?
Have checked attic, ventilation there, moor venting, etc all good. After one contractors advise, I installed a 12 X 12 stack vent and sealed off large ( 24 x30) gable end vents I had as he said the new theory was to discourage cross venting and encourage soffet venting up Thru to peak. We are confused, frustrated and cannot seem to get anyone to solution?
Can you help?
Trust me, ask 10 people ( contractors) and get 10 different answers :0(
There is more I could say, but will wait to answer verses bore you right now.
Thanks
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Replies
Kevin,
The interior side of your wall sheathing is wet because the sheathing is cold. It is a condensing surface during the winter. If warm, humid indoor air has contact with this cold sheathing, this type of condensation is to be expected.
Do you have reason to believe that this wall sheathing has been wet for years? Or did you only notice the moisture when the wall was opened up?
There is no way to figure out the problem of the "dirty dark water migrating down the outside of the vinyl siding" unless you post a photo of what you are talking about.
I doubt that either of these two problems has anything to do with attic ventilation.
Totally agree about the wet sheeting caused by cold on warm, I can try to send pic of siding. I guess the confusing part is that the insulation was not wet, the vapor barrier was good, mind you it was only 4 Mil required back then, now it's 6 Mil. I'm just not understanding how it can be so wet, when the insulation was dry and intact and the vapor barrier didn't seen jeopardized to such a degree to allow this kind of moisture / condensation?
Not to mention the water migrating out of the siding drain holes? obviously this is not a cut and dry problem to solution. Really appreciate your thoughts on this.
Kevin,
Of course it's always possible that your sheathing is getting wet from the exterior side. This might happen, for example, if you have exterior flashing defects that allow rain to get to your sheathing, or if you have recently had an ice dam on your roof that allowed water to enter your wall assembly from above.
These days, building experts don't recommend the use of an interior polyethylene vapor barrier in your climate zone. The three most important ways to keep your wall sheathing dry are:
1. Make sure that you have well installed flashing where required, and make sure that the flashing is integrated with your water-resistive barrier (usually asphalt felt or plastic housewrap).
2. If possible -- this isn't easy on an older house -- make sure that you include an adequate layer of rigid foam on the exterior side of your wall sheathing.
3. Pay attention to airtightness at all aspects of construction.
Keeping your wall airtight is more important than including an interior vapor barrier. For more on this topic, see these two articles:
Do I Need a Vapor Retarder?
Vapor Retarders and Vapor Barriers
Almost 8 years later and I’m just coming across your post.
I’m having a similar situation and am finding it difficult to find information, my guess is because most don’t have a clue what’s happening behind their walls unless they happen to open it up during renovations..
Ive opened up drywall in the second floor of my home to run some wires and hardwire a light sconce. In doing so, I did notice some black on the pink fibreglass insulation (home near Toronto, Ontario and built in 1985). Long story short, I ended up removing drywall, insulation and vapour barrier from the entire wall. Though attached, the vapour barrier wasn’t seam sealed and had a hole cut out for the receptacle, which was also not airtight. There was no condensation on the vapour barrier, and the fibreglass insulation appeared to be fine, other than some dark grey spots. The exterior sheathing however was more concerning in areas with black wet spots, and even frost. Typically in the area of the bottom and top plates. This didn’t happen while the drywall was down. The drywall came down because of this.
We also had our aluminum siding replaced about 4 years ago, and replaced with vinyl. At the same time the exterior also had insulation added or was “reinsulated”. Any idea what caused this or what I should do? I feel like others just convince themselves that it’s normal and board things back up and never worry about what they don’t see. I really want this to be normal but I’m not sure.
Thanks!