Window Wall Crack

medeek · Jul 2, 2016

A few months ago I designed a window wall for a residence in Ocean Shores Washington. The structural plan is the following:

I get a call back today from the owner that a crack has opened up at the prow/apex of the wall towards the bottom of the wall and has gradually gotten wider since about March this year. See photo below:

At the bottom the crack is about 7/16" wide. Looking into the crack I don't see that the wall wrap or felt has broken or stretched to any degree. Checking along the sill plate I don't visually see any displacement of the wall itself or cracking of the stemwall or any other settlement issues. Also inside there is absolutely no cracking of the drywall, see photos below:

Unfortunately, I did not take pictures of the framing before the wall wrap went up so I don't know if the contractors installed the straps that connected the walls at the apex, or even how they may have nailed the studs along this seam. I probed with a small screwdriver where the MSTA30 strap should be that connects the lowest headers and did not find a strap. Of course this doesn't mean its not there, just that I couldn't find it with the means that I used. The residence was framed mid November last year about 6-7 months ago during the rainy season, the wood was completely saturated as were the PSL columns which probably should have been better covered. The building official had looked at the crack and he figured it was due to the wood swelling and then shrinkage, with the amount of rain we get here there is definitely some validity to that argument.

At this point I would like to talk with the framers and general contractor to determine if they installed all of the straps per the plan. I'm doubtful if they will remember exactly what straps went where and sizes etc...

Ultimately I need to write a letter with a course of action for the fix, which may involve tearing up the window trim to check for the straps and possibly install more if required. At the moment I'm very disappointed since I spent considerable time and effort designing this wall so that something like this would not happen.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

medeek · Jul 2, 2016

If the two walls (2x8 studs) were moving independent of each other I would expect to see cracking of the drywall but that is not what I'm seeing and has me confused. Could it just be shrinkage of the trim boards around the window? I may have to call in another engineer who has more forensic experience than myself to give a second opinion. I inspected the STHD10 holdowns that are connected to the base of the PSL columns (5-1/4 x 7) and did not see any sort of twisting or evidence that any movement has occurred. Even if the crack appears to be superficial and is only the trim how does one prove it.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

Guastavino · Jul 2, 2016

My guess is shrinkage, think deck boards and how they shrink and a gap opens. And MC varies of course, and I doubt the trim boards were kiln dried or even HT.

With that said, I would ask the contractor, in writing, what types of straps they used on the wall. I.e. Did they use Simpson or USP? Or something non confrontational. If you say, did you install the straps, the answer will be yes! If you ask another question about the straps that is innocent, they might be like "straps, what straps?" And then you'll know whether they did or didn't. Or you can ask them directly and then go take the trim off to see. If they didn't do it, it's on them, at least that's how I see it.

The point of the question is to see if they did it without asking them directly.

As Uncle Joe (Stalin) said, make yourself into a sheep and you find out where the wolves are...

oldestguy · Jul 2, 2016

Is that a wood floor, with the run "perpendicular" to this "prow". Could be in more moist summer the floor expands and shoves the prow walls apart? Most movement seems at bottom. the photo shows part of foundation; any cracks? What is the predilection of the prow; North?

Triangled · Jul 2, 2016

assuming your drywall is attached to your parallam posts, i'd bet no drywall crack = no post movement.
I'd measure external dimensions such as window locations to prove that no other fundamental kinds of movement has occurred.
Then I'd focus on the exterior wood finishes, the trim as others have said above.

medeek · Jul 2, 2016

@oldestguy

If the wood floor was spreading the walls apart then I think you would see cracking of the drywall but as you can see there is none at the base of the wall. No cracks of any type in the foundation, or any other signs of movement of the wall relative to the foundation. If the wall have moved relative to the foundation you would possibly see the sill plate overshooting the concrete at the right corner, there was no sign of this.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

medeek · Jul 2, 2016

The PSL posts shoot down through the floor and rest directly on the sill plate. The rimboard is cut at those locations to allow for the posts to drop down through it. I know this is built per plan since I have photos of it, see picture below:

If the wall is moving then the posts would move which would cause the rimboard to translate with the posts and hence the ledger board attached to the rimboard would move as well. From the pictures above you can see there is no significant separation of the ledger boards at the prow.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

Ron · Jul 2, 2016

Since no drywall cracking, you have no differential direction movement on the inside, just the outside.

I'm with others....Look at shrinkage in the trim. Remove the trim at the corner and you'll likely see that all below is ok. Check attachments and types of fasteners used for the trim. See if you have any displacement in the fasteners or any elongation in the fastener holes.

You might also get them to seal the intersection of the metal flashing above the rim board. It is allowing water into the miter at the corner. You will also note that the miter and the flashing have not separated the same distance as the trim above, again indicating the issue is outside the primary structure.

oldestguy · Jul 2, 2016

If you can, I'd look to see if any water got into the insulation and "ran" to the bottom. High moisture there could cause those larger studs to swell laterally (perpendicular to grain)and shove the outside wall out. The swelling also pushes inner wall tighter together. Longitudinal swelling or shrinkage usually isn't much. Why would worst problem be at bottom?

dhengr · Jul 2, 2016

Medeek:
I think the wall is moving (walking around a bit) out at its outer face. The angle btwn. the two planes may be closing a bit, in some areas. It is moving in plane maybe do to a bit of shrinkage and due to lateral loading, and it is moving out-of-plane due to lateral loading and how this is transferred btwn. the two wall planes. I would really like to see your detailing, in cross section, (and the actual built detailing) at that corner joint. Your detailed horiz. straps will not solve the problem as I see it, and they should be neatly bent and tensioned when applied. You need several fairly heavy ga. steel straps 10,12-16" long, with two 5" (plus, plus, on each wing for the angle gap in the framing) wide wings, with the angle btwn. them to match the angle of that corner joint. These are applied parallel the long open joint/gap btwn. two 5.25" x 7" PSL columns and, in effect, they transfer shear flow as the fillet welds would btwn. the web and flange of a fabed. pl. girder. They prevent the two planes from sliding vertically, and parallel to each other. The walls are parallelograming (and moving, walking) w.r.t. each other, and you have to stop this. You also need solid blocking in the gap btwn. the two PSL columns behind these shear transfer plates and your straps. I’ve seen these kinds of problems and joint separations a number of times on these kinds of angled corners where they had two separated wall planes, at angles, which were not well connected together to transfer this shear load along the joint length.

medeek · Jul 9, 2016

I'm still waiting on the owner to proceed further. I would like to remove the trim board at the apex and peel back the house wrap so that I can properly inspect the junction of these two walls. I still don't know if any of the straps were installed and what is the state of the solid blocking between the PSL columns and actual applied nailing pattern. At this point I cannot prove that the gap is due only to shrinkage so further exploratory is necessary.

@dhengr

I'm tending to agree with you. With the junction of the two walls non-coplanar the sheathing provides zero strength and stability between these two walls. It is all on the fasteners and straps. These two walls need to be stitched together.

I will provide further updates once I have opened up the wall for inspection.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

EngineeringEric · Jul 10, 2016

Medeek,

It looks like the HO/Contractor placed that white sealant? on other locations of this exposed trim? are other pieces of trim moving? Also, I am surprised that the trim at the the angle in concern was not taper cut and glued together. None of that is structural just observations and things worth noting.

It looks like a finishes issue to me, and one that will get worse with time and eventually mess with the structure.

Things worth noting during demo. how is the trim installed, condition of fasteners (rusted, bent, pulled out, too short), if the boards shrink they usually pull back on both ends (gaps on both ends?), maybe the obtuse angle looks 2x as bad since it has 2x the joints shrinking with nothing resisting pull back.

Good Luck!

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Window Wall Crack

medeek

Structural

medeek

Structural

Guastavino

Structural

oldestguy

Geotechnical

Triangled

Structural

medeek

Structural

medeek

Structural

Ron

Structural

oldestguy

Geotechnical

dhengr

Structural

medeek

Structural

EngineeringEric

Structural

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