View Full Version : Ceiling crack help

Charlie Velasquez
09-24-2006, 1:02 PM
Single story ranch with truss construction as in diagram.
Living room/ dining room is L-shaped 16 X 33. Trusses span the entire 33' length (edited this last sentence)
When we moved in 9 years ago the ceiling had a crack that transversed the 16' width that is directly under the plates where the truss members meet.
I cleaned out the crack and retaped. Repair lasted a year. We had 5" of snow, then ice, then another 14" of snow in 48 hours that winter. Crack came back. I have lived with this for last few years, but it has bugged me. We are repainting the room this month and would like to repair it permanently. But I must be realistic. We have those kind of snows if not at least once every winter, then certainly every two or three winters.

This is what I am thinking:

Cut out a 2 foot section along the crack and replace the drywall so there are no joints (still have the single butt joint) under the place where the truss members meet. But I say to myself, "But I am sure the original sheetrock people did not have a 16 foot joint right there originally, so it probably cracked the drywall. So, would it happen again?"

I have heard there are some new and improved joint compound stuff that is elastic-like. I have not been able to find such products on the internet, But, if such a product exists, I could just clean out the crack again and nylon tape and this wonder elastic compound may do the trick.

Add another layer of 3/8" drywall to the entire ceiling, making sure no fasteners are directly below the truss joints, using mostly construction adhesives to allow some give.

Any suggestions or the name of an elastic joint compound would be greatly appreciated.


Richard Wolf
09-24-2006, 1:16 PM
I think you are trying to deal with the effect and not the cause. You should get up in the attic and look at the trusses. I would think that sistering some new rafters into that area would solve your problem. Then you can repair the sheet rock as needed.


Matt Warfield
09-24-2006, 1:24 PM

I would recommend inspecting that truss and its neighbors very closely for cracks and/or cross bracing which isn't securely attached. The extra flex could definitely crack a joint line. Also, when you repaired it the last time, did you notice if it were a joint line or if it was torn paper? I'd be very surprised if it were the latter. Either way, if you want to permanently fix this, you'll need to identify the cause.

Let me know if you need a hand. Depending on the distance from Cedar Rapids, I may be able to assist.

donnie wood
09-24-2006, 2:19 PM
I noticed in your post that you have a 16 ft crack, that is a big problem because the sheetrock has torn itself or there is a 16ft seam. If there is a seam then there possiblely was a loadbaering wall there at some time. What has been said before is the way to go. First check the trusses, see if they are factory or homemade. I factory they should be made to carry the load. If the drawing you made is the way they are made then I would say they are homemade. The braces should meet at the gable.

Russ Filtz
09-24-2006, 5:10 PM
Probably not coincidence the crack is directly under the "truss" connections. Would tend to agree this truss design does not look "factory", unless it were designed for max headroom in case of attic build-out? If so, the rafters should have been beefed up.

Hopefully we have some structural engineers lurking? I agree it seems the trusses need beefed up with some more connections to smooth the load out. Could also be the way they laid out the sheetrock too. You might have a seam right at a high stress-deflection point on the rafters.

Ben Grunow
09-24-2006, 11:09 PM
What size are the ceiling joists and rafters? Those trusses are definitely not factory made as suggested above (those braces transfer the bending from the rafters directly to the joists where factory trusses would use simple triangulation to allow the spans in the trusses to be shorter and place the joists in tension instead of asking them to accept roof load).

Looks to me like the bracing was added to stiffen the joists, maybe after an interior wall was removed at some point, as the span is too far for even engineered lumber.

I would look to an engineer to help design a truss using the rafter and joist sizes you have and retrofit your roof using plywood, PL400 and screws as gusset plates.

Another option would be to install a structural ridge (assuming the rafters are sized properly) under the existing ridge. THis would be an LVL that would need to be supported by load bearing walls but would allow you to remove the existing bracing and replace it with new hangers from the new ridge beam (just 2x4s with bolts through ridge and joists). THis would reduce the span of the ceiling joists and not transfer the rafter loads to the joists. All designed by and engineer unfortunately.

I hope this helps. Maybe the info on the rafter and joist sizes will help with more solutions.

Charlie Velasquez
09-25-2006, 7:02 PM
You are all right. I really need to address the underlying cause of crack if I want to do it right.
The mom of a former student is a structural engineer, but she does things like dams and bridges. Called her to see if she could recommend someone that does houses and she offered to take a look at it. Thanks for re-enforcing what I should have remembered from past experiences: it really doesn't pay to do it half-way.