Thread: Truss Bumps in Drywall.

I wasn't sure where to post this question, but I'm pretty sure it's something truss related, so here we go. The photo is of some odd bumps in a bedroom drywall ceiling, and the hallway to the interior had just about the same thing. I also observed this in the kitchen ceiling. This is a higher end, 20 year old frame house. These bumps or bulges appear to be caused by the trusses pressing down into the drywall, causing it to displace downwards at each truss pressure point.

Why is this happening, and why does the drywall resist to the point of failure instead of just going along for the ride? We saw nothing odd about the trusses, and there are no other significant flaws in these ceilings and walls.

Thanks a lot for any insight you may have on this.

I have no idea, and have never seen anything like this. Obviously something is amiss. Definitely in need of further investigation, starting in the attic to see whats what.

Bizarre! Never seen that. I saw some possible truss lift yesterday, but your photo doesn't look like truss lift. Do you have any attic photos of this?

I haven't seen that before either, but I have seen framing which could allow it.

Is that an interior wall?

If so, the wall framing may not have been framed all the way up to the trusses, the drywall on the walls was installed up to the ceiling drywall. This leaves a gap above the wall framing between it and the trusses.

The trusses likely settled down to the top of the wall framing, causing the trusses to crush the drywall like you see it.

It's possible the trusses were shimmed with improper material that squashed down over time. Just an idea. , did you check the truss to upper plate connection?

Originally Posted by Jerry Peck

I haven't seen that before either, but I have seen framing which could allow it.

Is that an interior wall?

If so, the wall framing may not have been framed all the way up to the trusses, the drywall on the walls was installed up to the ceiling drywall. This leaves a gap above the wall framing between it and the trusses.

The trusses likely settled down to the top of the wall framing, causing the trusses to crush the drywall like you see it.

Interesting conjecture. I think that would have crushed the drywall on the walls rather than creating the bump in the ceiling drywall. This inspection needed Holmes. He would've just ripped that ceiling open to find out what was going on!.

Truss movement due to the difference in temperature/moisture between the upper and lower member.
I've got a diagram somewhere but it would take more time than I have to find it.
Seems that this has been addressed here before.
The wall should have been framed to allow some movement of the truss before causing damage.

BSI-023: Wood Is Good . . . But Strange ? Building Science Information
Check out figure 10 , 11, and 12.

Originally Posted by Lon Henderson

Interesting conjecture. I think that would have crushed the drywall on the walls rather than creating the bump in the ceiling drywall.

It crushed the drywall on the walls too - just not as much and it is not as easy to see because you are looking at the wall, where you are looking across the ceiling.

I would like to see a photo of that from the attic - that is where I would have gone if at all possible.

One possibility is poor patching after nailpops occurred due to truss uplift. Someone may have also added a few screws to try to stop the problem and then patched. When the trusses dropped again it popped the large patches. Just a guess.

Are you sure it was engineered truss roof and not a stick built roof? Do you have any attic pictures?

Michael,

As others have said, there has to be something else going on in the attic that changed at some given point, for the truss framing to be putting that much pressure and visible damage on the interior drywall.

If you did get into the attic over those suspect areas, or just looked from the access opening, if these are interior walls were there sections of wood put down that the seller created another 'room' up there? Do they have a boatload of storage items/file boxes of any considerable weight, that are stacked in those areas? If either, my guess would be that a considerable amount of weight has caused the bottom cords to at least sag if not separate from the original construction design and junction plates.
If those are exterior wall areas, and however close that affected hallway section was, did they re-roof at some point? Those areas may be where they 'loaded' the tiles or shingles when taking off the truck, and there was an exceptional amount of weight put on those truss areas that it wasn't designed for.

Steve L.

I found the diagram.Truss uplift.JPG

The diagram shows uplift but remember what goes up must come down and the downward force can be just as strong.

I've been recovering from minor knee surgery, so I've been using another inspector to do roofs and attics for me, and he had other work that day, so he had already left before I found this ceiling problem. Rather than trying to go up there at that time, I knew I had to revisit the property to fetch my radon monitor (13.7 pCi/l) yesterday, and that would give me a couple more days of healing. In the meanwhile, you all gave me the exact places to look, and what to look for.

I went back last evening, took some Ibuprofen, gritted my teeth, and got these photos. All areas involved are interior walls, under a modern engineered truss attic structure system. It appears that the section of truss that meets the wall framing was cut back maybe 3/8 in. for whatever reason, but then didn't properly meet the wall frame. I had to fold over a business card to get past the nails, but it fit quite loosely, and there was still plenty of room between the truss and the wall frame, which means the ceiling damage could get worse if it's not corrected.

Thanks a lot for your help with this one!

Michael,

Those holes the NM cables are coming up through the top plate should be fireblocked (sealed with a proper sealant - that expanding foam which comes in cans marked as "Approved for fireblocking" or similar wording (and is typically pinkish/reddish in color) works well for that purpose. There are other products, but that is the "quick and easy" way for builders to address it.

But don't let them get away with the ivory/cream color expanding foam which says that it is good for draft stopping (two words) ... that stuff is suitable for stopping drafts around windows and doors, but is not rated for "draftstopping" (one word) or "fireblocking" (one word).

Wow!! nice pictures of the situation.... Thanks for braving the physical ailments to capture a few photos for us. I was impressed with your first picture and have never seen anything like that. Are the trusses poorly supported? They shouldn't need support at the center of the span .... maybe the gussets are poorly or inadequately pressed into the 2x's ? Strange conditions. I would suggest an engineer - just to get it out of my lap.

A guess: The framers added that wall (or walls) after the trusses were set. When they tried to stand the walls, they couldn't get them to rotate in under the trusses so the idiots removed some of the truss wood with their framing axes where the walls went and then failed to add shims when they got the walls into position. Of course, shaving the trusses is still wrong, but if they had shimmed the gap, we wouldn't see this problem.

Originally Posted by Lon Henderson

A guess: The framers added that wall (or walls) after the trusses were set. When they tried to stand the walls, they couldn't get them to rotate in under the trusses so the idiots removed some of the truss wood with their framing axes where the walls went and then failed to add shims when they got the walls into position. Of course, shaving the trusses is still wrong, but if they had shimmed the gap, we wouldn't see this problem.

Sounds plausible, even likely, and with framers like that, it would also explain why so much (distance) was removed from the bottom of the bottom chord ...

It is always amazing to see the different ways people figure out how to do things wrong!