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Leroyb86 10-05-2010 11:02 AM

Drywall joints cracking and bulging in attic conversion
Hi, hope someone can assist with this problem. I've been converting attic space in my house into two bedrooms, a bathroom and a play area. In one room where the drywall has been finished (but not yet painted), I've been finding cracks along the seams and also areas where the seams are bulging, likely due to the expansion and contraction of the roof, particularly now that we are entering the cold season again. The problems areas are both on the ceiling (sloped ceiling, drywall attached to roof trusses) and some minor areas on the knee walls, which I built myself.

Is there anything I can do to prevent this? As I start the other bedroom (the drywall is up but not finished) and then the other rooms, I would like to be able to avoid this problem, if at all possible.

Thanks in advance.

cbzdel 10-05-2010 11:57 AM

are you sure the structure is capable of holding the additional load?

Leroyb86 10-05-2010 03:32 PM

Yes, had a structural engineer assess the area before I started work. As I said, I'm fairly certain the reason has to do more with expansion and contraction than anything else. Just not sure what to do with it.

cbzdel 10-05-2010 04:56 PM

Got any pictures of what is going on, then we can get a better idea of whats going on.

steveel 10-05-2010 05:40 PM

also, what is the location of this building? knowing climate may give some of these guys a clue

Leroyb86 10-05-2010 07:58 PM

Example pic
2 Attachment(s)
It's hard to get a good pic of the affected area, so I've attached one of the room in question (it opens up on the right-hand side) and another that shows more of the visible seam in one of the knee walls.

Some of the cracks are simple, hair-line cracks.

The location is near Pittsburgh, Pa.

steveel 10-05-2010 08:35 PM

I'm in PA too. I'll watch with interest since we may do some of this ourselves. Have you seen
It's excellent.

Gary in WA 10-05-2010 09:46 PM

If the crack is over the corner of the built-in, you probably broke the drywall there, a no-no. You should have cut a board in the shape of a backward "C" and float the ceiling there. Pull the screws to let the ceiling float on the wall, so the roof can expand and contract with the seasons:

If a bedroom, I hope you have another window bigger than pictured for proper egress:

If a joint there, did you pre-fill it with setting compound?


Leroyb86 10-06-2010 06:58 AM


There is a joint there, and it was prefilled with joint compound before being finished. I used regular paper tape there.

BigJim 10-06-2010 10:02 AM

How are the ceiling/rafters vented?

Gary in WA 10-06-2010 01:47 PM

That is why. The joint should have been as I said. The gap should have been "V" notched if at panel ends and filled with a setting compound not all purpose or lightweight. You will get movement there due to the roof flexing from expanding and contracting of the seasons, even from morning/night temperatures. The movement will be magnified because of the built-in, making the joint that much shorter = weaker existing tape=weaker still from wrong mud = wrong joint break area. In framing, there is probably a horizontal header 2x, butting the king or jack stud: the weakest framing area. Two framing members nailed together will separate slightly after heated to room temperature unless framing is acclimated or nails are installed slightly angled to pinch that joint together. A little stronger if you had broke joint on king stud only. To fix-- cut a 16" section out each side of existing joint for a 32" replacement piece. Next common stud from king to next cripple stud over built-in. Tip: Snap a blue caulk line down the middle of the sloped ceiling/flat ceiling joint for a guide. Fill low areas only with setting type mud compound to meet the line-- both sides, to straighten that joint perfectly. Use a wide knife. The lightweight has less adhesive in the mix, poor for taping (holding power) compared to all-purpose.


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