Help/insight request. Drywall problem in new bathroom.

[Ash Peltier]

long time lurker, first post.

last summer I added a dormer bathroom to my second floor. Everything went great, I learned a ton. However, when the temperature plummeted in Michigan last month, I discovered a bubbly and moist drywall tape seam on the ceiling. I figured it was condensation under a incomplete / dry tape spot. after getting past the frustration with myself, I repaired the spot and it looked perfect including two layers of primer and a layer of paint. Today however I find the same situation developing again. in the same spot. I am quite confident that the roof isn't leaking, I used iIWS water guard on the whole roof. I do not know how was the moist air got underneath the paint and into that seam, though. I disrupted the paint along the bubbly seem, to let the moisture evaporate.

because the width of the rafter space at the end of the roof was short of standard, I am afraid that my insulation technique was inadequate. even if there was no insulation, though, why would this seam become wet and bubbly? I would love any insights.

I'm usually not happy unless I have a project to work on, but I don't want to waste more time chasing the wrong solution to this problem. Thanks in advance for any insights.

 

[Ash Peltier]

here is a photo of the attached affected area.

 

[green.bubbly]

Did it just peel and flake like that or is the picture after you poked at it? Do you have a vapor barrier above the drywall?

 

[Highlux]

That is water. You have a leak. Get up in the attic and take a look.

 

[HotrodHR]

If you are absolutely certain there is no leak you've got a major condensation problem... You said it started when the temp dropped... My guess is no vapor barrier and no or little insulation. Is this a full bathroom with shower? Without proper venting you add to the problem with condensation on the inside.

 

[jmlcolorado]

I agree with all the posts above.
Vapor barrier needs to be above the drywall, below the ceiling joists. Insulation needs to be thick enough to prevent heat loss through the drywall.
And if the exhaust fan dumps into the attic, that's adding to the mess.
Might want to add foil tape around the joints of the exhaust fan too to help seal it up, if it's rigid duct.

use at least semi gloss paint as well.

 

[green.bubbly]

I agree with all the posts above.
Vapor barrier needs to be above the drywall, below the ceiling joists. Insulation needs to be thick enough to prevent heat loss through the drywall.
And if the exhaust fan dumps into the attic, that's adding to the mess.
Might want to add foil tape around the joints of the exhaust fan too to help seal it up, if it's rigid duct.

use at least semi gloss paint as well.

Hey Jim, my son moved to Highlands Ranch about two years ago. He is actually in Littleton I believe. His wife is from HR. Nice area out there. If you ever see a Cajun driving bad in the snow up there, it is probably my son.

 

[Ash Peltier]

Such ball dropping on my part. Had to get clever. Thanks for the feedback, evidently my foamed in rigid board in that rafter space was a bad idea.

 

[p_mori7]

It should look something like this before you put up the drywall (behind & above the heater):



You could also add 1x3 strapping perpendicular to the studs & rafters, this will create an additional air space (more insulation) and makes for a wider space to screw the drywall onto.

 

[Scott H in Wheaton]

Its becoming more common this winter. I do an attic inspection and find the space LOADED with condensation. Sometimes its frost and ice. Comes from too little insulation on top of the ceiling and not enough flow-through attic ventilation.
This also contributes to the attic space being warmer than it is outside, so snow melts at the top of the roof, then the runoff hits the freezing cold edges of the roof and turns to ice.
It continues this cycle and builds up a nice little ice dam around the edges of the roof.
When the temperatures fluctuate the frost and condensation in the attic drips down on the insulation and floor joists, eventually getting to the drywall.

 

[jmlcolorado]

Hey Jim, my son moved to Highlands Ranch about two years ago. He is actually in Littleton I believe. His wife is from HR. Nice area out there. If you ever see a Cajun driving bad in the snow up there, it is probably my son.

HA!
I'm technically in Littleton, but surrounded by highlands ranch.
As far as keeping my eye out for seeing bad drivers in snow......... They seem to be multiplying.

 

[jmlcolorado]

Such ball dropping on my part. Had to get clever. Thanks for the feedback, evidently my foamed in rigid board in that rafter space was a bad idea.

Ah yes. That could do it!
I assume you have a ridge vent rather than a gable vent or turtle vents?
Might be a chore getting all that foam out of there. It might end up being easier to wait for fair weather and pull the ridge vent off, replace, and put on new ridge cap shingles

Still kinda strange that it's only appearing in that one spot.

 

[Kevin54]

Where is the duct for the bathroom vent ran to? It may be the fact too that you are getting truss rise, and it is affecting the joint, therefore breaking it. I know that in the winder, we get truss rise and it affects the wall that shares the master bedroom, and the common bathroom.

If you are getting this now for the last two winters, I think if it were me, I would cut out the section of drywall and see in behind it as to what is actually going on. If it's moisture, you will need to cut out the drywall anyways to repair things. And you don't want mold starting behind the drywall if it is moisture.

 

[Garage Dog]

Its becoming more common this winter. I do an attic inspection and find the space LOADED with condensation. Sometimes its frost and ice. Comes from too little insulation on top of the ceiling and not enough flow-through attic ventilation.
This also contributes to the attic space being warmer than it is outside, so snow melts at the top of the roof, then the runoff hits the freezing cold edges of the roof and turns to ice.
It continues this cycle and builds up a nice little ice dam around the edges of the roof.
When the temperatures fluctuate the frost and condensation in the attic drips down on the insulation and floor joists, eventually getting to the drywall.

^^^thinking about these things is where you should start. I don't think we have enough information to diagnose the cause of your issue, but Scott H does the best job of summarizing the potential causes above.


Do you have exhaust fans? How are they vented? How well is the entire attic insulated? How is the attic vented? Could snow be blocking the ridge vents on your roof? Do you have access to the dormer/attic space above the bath? What is directly above that tape line?

Such ball dropping on my part. Had to get clever. Thanks for the feedback, evidently my foamed in rigid board in that rafter space was a bad idea.

Foamed in rigid insulation isn't necessarily a bad thing, just depends how it was installed. Did you fill the cavity solid to create a "hot roof" because of limited space above this bath, or did you still leave a space above the insulation for venting/air flow?

Google "hot roof" then Google "how attics are vented" or something similar to give you a bit more insight to determine how things should done if you are confident this is not caused by a leak of some sort.

More information and a few more pics might help get this narrowed down.

GD

 

[tcianci]

I have read all the pseudo science here... you have a roof leak, sorry.

 

[Ash Peltier]

thanks again for all the input. I took the drywall off of that rafter space, and about a cup of condensation poured out. I removed all the foam and replaced it with craft backed fiberglass. I made sure to tape all the edges to the existing vapor barrier, thoroughly, and then caulked around the seams of the new drywall. I've got the first layer of Mud up with tape, and the dehumidifier and space heater are keeping the room nice and warm and dry. I think my foamed in insulation did not establish an effective vapor barrier. There was water and ice down near the soffit. I left it open to dry before I repaired it. the new dormer has vented soffit s and ridge vent. the rest of the house has solid soffits and turtle vents. I'm sure I will have to deal with Putting extra holes in the existing soffit to facilitate crossed venting.

 

[Ash Peltier]

in hindsight, albeit incredibly frustrating, the drywall seams failing revealed a much more serious problem. If it hadn't, I'm sure I would have ended up with structural damage from the condensation. On another note, is a perfect vapor barrier ever really possible? Obviously, keeping humidity down when it's very cold outside is crucial, but do most houses have some (even small) degree of condensation in thier attics or Rafter spaces?