Truss uplift?

[Darin Redding]

Inspected this home yesterday. Home built in 2000. Client is concerned with the cracks noted at interior walls located in the center of the home. From the attic, you can see how the installer used proper truss clips, did not nail the truss to the interior walls, but notice in the pic taken from the attic how the drywall for the interior wall surfacing travels above the top plate of the interior wall. This was typical for the trusses running ten feet or so from the exterior wall.

My thinking is that as the bottom chord of the truss swells and straightens out, it compresses the drywall resulting in the bulge you see in the photo below (taken with a flashlight to accentuate the shadows). In winter months one would expect the bottom chord being buried in insulation to remain dry, while the web and top chord swell from moisture in the attic causing the opposite effect, or the characteristic truss uplift. What is exhibited here is the opposite of this phenomenon. Note the picture showing the view from the exterior appears to show that the truss has raised and exposed a gap between the exterior stucco wall and the top plate.

Do you see any issues with this? It is easy to simply recommend a review by a structural engineer but I would like to hear from some experts as to what is happening here. There was some settling issues (doors out of square, tile countertop falling away from backsplash, etc.)

Thanks for looking!

[Sean Fogarty]

Its hard to tell from your photos but my home uplifts in the center around the kitchen and hall. I would estimate between 1/4 to 1/2 inch overall and the caulk around my crown moulding is torn from this.

Trusses uplift in the winter not compress.
The ceiling will pull away in the winter and fall in the summer.


If you have cabinet and wall movement you may have some more serious issues. I doubt a truss could lift enough to mess with a door. Structural settlement will also cause ceiling to wall seperation. If your unsure state what you think it could be but only someone with structural experience can make a true determination.

Only inner walls should be affected by uplift. If you have any outer wall showing crakcs or issues then its not the trusses.



Here are a couple of photos of my home so you can get an idea.

[Robert Ernst]

I went to a house just the other day and the pictures look almost the same. There was some cracking at a drywall seam. According to a contractor I know this is somewhat normal since the truss is allowed to float.

[Darin Redding]

Thanks for the comments. I understand truss uplift but there seems to be different forces at work here. I would expect uplift in winter even though in San Diego our winters are mild.

Is it that the drywall installers simply installed the wall drywall too high (chord was bowed up and there was a gap between the trusses and interior walls), and since then the truss has dried out straightening the bottom chord, compressed the drywall?

Seems reasonable but of course I would never state as much in a report. This is simply an intellectual exercise for all of us.

Thanks and I look forward to reading additional comments.

[Tim Spargo]

Roofing type? Any pictures a bit farther back from d/wall and/or fascia from affected area? Also, was the d/wall defect adjacent to the exterior wall or ?

The gap between the top of the stucco and the blocks is interesting. It looks like the right half of the left bay pictured has some stucco left on it, indicating movement post construction. Curious.. on the areas pictured would there be an interior partition adjacent to these areas? Source of water under a nearby partition and expansive soils can do all sorts of weird things... not an official guess, just a thought.

If it were comp. shingles, I may have pushed up on the fascia to see if I could simply lift the trusses off the plates as wind damage or poor attachment could be to blame for gap and d/wall damage. I have seen nearly exactly that after a wind related event. If it were Tile, I'm not superman.. that stuff is heavy

[Darin Redding]

Yes Tim, the roof was tile. There were no nearby adjacent interior walls from the exterior picture. I agree the movement was post construction. The interior wall exhibiting the crushing effect of the truss was parallel to the exterior wall along the same truss lines, approximately 15 feet from the exterior wall. So the trusses were running perpendicular to the interior and exterior walls in question.

Any other thoughts?

[ROBERT V. YOUNG]

Here are some truss and rafter tie Downs brackets.
I do not believe uplift but did you take a laser level or spirit level angles of the walls, doors casings, floor pitch ?
Look for window being off square ( opining is the casements and doors being off square. Hrad to close. Plant the spirit or laser level all over the building. Look for missing load baring walls. Hard wood flooring will be a good place to find pateren changes and color diferences in the vertical laided pieces.
Bring a laser level to your inspections
.http://www.sears.com/shc/s/p_10153_1...=1327292671525

[Mark S. Tyson]

Originally Posted by dredding

Yes Tim, the roof was tile. There were no nearby adjacent interior walls from the exterior picture. I agree the movement was post construction. The interior wall exhibiting the crushing effect of the truss was parallel to the exterior wall along the same truss lines, approximately 15 feet from the exterior wall. So the trusses were running perpendicular to the interior and exterior walls in question.

Any other thoughts?

It is hard to really make a determination from the limited information, but for the sake of conversation I will offer up a scenario.

This condition as posted earlier is consistent with truss deflection and possibly the result in poor construction sequencing.

All truss members deflect to some degree depending on span and is accounted for in the design drawings and is the reason that interior non load bearing walls must clear the bottom cord of the truss.

In the past i have seen homes where the gypsum board was installed and finished before the roof tile was loaded onto the roof. Then after normal deflection occurred the gypsum board developed cracking much like shown in your earlier photograph

[Tim Spargo]

Originally Posted by dredding

Yes Tim, the roof was tile. There were no nearby adjacent interior walls from the exterior picture. I agree the movement was post construction. The interior wall exhibiting the crushing effect of the truss was parallel to the exterior wall along the same truss lines, approximately 15 feet from the exterior wall. So the trusses were running perpendicular to the interior and exterior walls in question.

Any other thoughts?

Fell asleep at the switch

Almost as though the pictured interior wall is acting as a fulcrum, or a portion of the exterior foundation has heaved adjacent to the pictured stucco gap.... I could see the crushed effect of the d/wall for causes like Mark said.. but with that gap at block line in the same "neighborhood" as the other defect, I'd suspect some type of differential settling or expansive soils.

[Dan Bowers, CMI]

Darin -

I'm gonna make a wild guess and say you've probably done the inspection and moved on. Therefore without an expert in there looking at it head-on, you're just taking a WILD butt guess by listening to us. I always enjoy being around a gambler.

Look for a Truss manufacturer, distributor or competent and licensed framing contractor, etc ... Describe the condition, recommend service and correction and move along.

[Darin Redding]

In the past i have seen homes where the gypsum board was installed and finished before the roof tile was loaded onto the roof. Then after normal deflection occurred the gypsum board developed cracking much like shown in your earlier photograph

But interestingly, the space exists between the top plate of the interior wall and the bottom chord of the truss. So after loading, the chord dropped and eventually returned to it's starting position? Seems odd. But I'm no engineer so who knows.

[Darin Redding]

Plant the spirit or laser level all over the building.

Hmm... seems to be crossing the line from a home inspector to an engineer, no? I tend to shy away from tools and techniques that might make people think I really know what I'm doing like using laser levels, performing manometer surveys, etc.

I do bring my 6' level with me but it rarely makes it out of the van. Unless I'm alone and can pull it out to check something without being noticed.

[Darin Redding]

you're just taking a WILD butt guess by listening to us. I always enjoy being around a gambler.

This is simply an intellectual exercise and I appreciate you participating. Gambler? Never. I enjoy my house, cars, etc. too much for that. Of course, I recommended further evaluation by a licensed structural engineer and possibly a soils specialist (we have lots of expansive soil here in San Diego) and left it at that.

As an addendum, an engineer did visit the house following my recommendation and determined that the trusses may have been engineered improperly. All other houses in this development of newer houses have the same type of roof.

[Greg W. Mathias, CCHI]

Is there a beam holding up the floor? Can it be adjusted? From the pictures it seems to me that the floor is sagging not the trusses lifting up. Just my guess!!

[Darin Redding]

Is there a beam holding up the floor?

This is slab on grade Greg. That's not to say the floor movement is not a contributing factor. Could be. Take a look at some other pics showing the many wall patches that have been done more recently in an attempt to sell this house. This is one of the few times I actually preferred to do an inspection in the evening hours as the play of light from my flashlight really accentuates the recent repairs. And yes Robert, some of the doors in the home did not close properly and were out of square. Let us not forget the horizontal crack in the stucco running along the entire east elevation. So is there movement? Most definitely. But unless the interior non-load bearing wall heaved in the upward direction causing the drywall bulge and cracks noted on my first post, some other forces are at work IMO in the roof framing.