Uncommon Truss Profile

[TRAK.Structural]

Did an evaluation at a townhouse property earlier this week and came across a truss profile I haven't seen before. It's a gable roof, but the ceiling has vaulted rooms at each end of the truss and a flat ceiling in the center portion. My guess is that the perpendicular wall below the transition between flat and vaulted ceilings is carrying the load from the truss but I'm not totally sure. The truss bottom chord is basically just toe-nailed to the top of the wall (see pictures). Think that interior wall is load bearing??

 

[XR250]

My vote is it is intended to clear span

 

[phamENG]

I'm with XR on that. Though I wouldn't remove that wall without careful verification. And while it was likely intended to clear span, the wall is probably doing at least some work (assuming it has a load path below it).

 

[jerseyshore]

Though I wouldn't remove that wall without careful verification. And while it was likely intended to clear span, the wall is probably doing at least some work (assuming it has a load path below it).

I might get this printed on a T-Shirt for site visits and just point to it when they ask the question.

 

[XR250]

Well as soon as the wall is removed all the improperly braced chords and webs will fail.

 

[KootK]

I vote bearing. With that 2x4 bottom chord across the attic, the truss wouldn't have any meaningful shear capacity across the middle. That would surely fail the truss if it were designed to support any unbalanced snow loads etc. Granted, this assumes competent design...

Put another way, I see nothing other than general conservatism to suggest that the interior walls are not bearing.

What are the lengths of the three spans?

 

[XR250]

With those spindly chords, I believe KootK may be correct.

 

[TRAK.Structural]

I vote bearing. With that 2x4 bottom chord across the attic, the truss wouldn't have any meaningful shear capacity across the middle. That would surely fail the truss if it were designed to support any unbalanced snow loads etc. Granted, this assumes competent design...

Put another way, I see nothing other than general conservatism to suggest that the interior walls are not bearing.

What are the lengths of the three spans?Typically the outer spans with vaults are about 12 feet, central flat ceiling area is about 8 feet.

Typically the outer vaulted spans are 12 feet and the central area is 8 feet.

There is one area of interest where only one end is vaulted for 12 feet and the remainder (20 ish feet) is flat ceiling and clear spans to the other exterior wall. This is at the hall/stairwell. At this location there is an ominous looking crack above a door opening at the interior wall in question. The ground floor beneath this location is pretty wide open so maybe a flush transfer beam is hidden in the floor somewhere. Regardless I think the wall is taking some amount of load that has produced this crack....

 

[phamENG]

At 32', 2x4 chords aren't a big surprise, though the profile adds some complexities that would likely drive up the size in a well thought out and designed truss. So my guess is that it was intended to clear span, but those walls and whatever framing is below them is stiffer than the truss and has, therefore, taken some load.

Caveat - I'm in a 10psf ground snow load region, so gravity loads on trusses here are pretty light. Higher snow load areas may be accustomed to larger chords on a 32ft truss.

 

[GaStruct]

I vote bearing. What does the floor plan look like? If that interior wall is continuous through the length of the building without jogs, I'd say it was an intentional bearing point.

For the floor below I often see LBW supported by perpendicular joists. What does that floor plan look like? Is it feasible the wall can be supported by the joists in the open space you mentioned? You can use a stud finder to figure out the direction of joists.

These are the things I would look at to confirm.

 

[TRAK.Structural]

I vote bearing. What does the floor plan look like? If that interior wall is continuous through the length of the building without jogs, I'd say it was an intentional bearing point.

For the floor below I often see LBW supported by perpendicular joists. What does that floor plan look like? Is it feasible the wall can be supported by the joists in the open space you mentioned? You can use a stud finder to figure out the direction of joists.

These are the things I would look at to confirm.

The wall is continuous and a straight line shot all the way across the home at the upper level. See pic below for ground level, the wall in question is approx above where I drew the red line.

 

[SinStrucEng]

At first I also thought that it's a load bearing interior wall, based on your description and sketches. But seeing the ground level picture, I now have doubts. If the wall was load bearing, the structure must have some continuity down to proper founding at that location... Second floor joists are framed parallel to your red line, so the wall above is parallel with the joists as well. Nothing below the wall? Seems like an ordinary partition to me.

That said - maybe there's a flush beam in the floor plenum beneath the wall? Is that a possibility? Or double/sistered joists? I'd explore those possibilities before making a call.

My general rule of thumb is - if there is ever any doubt - leave in place and do not remove.

 

[TRAK.Structural]

At first I also thought that it's a load bearing interior wall, based on your description and sketches. But seeing the ground level picture, I now have doubts. If the wall was load bearing, the structure must have some continuity down to proper founding at that location... Second floor joists are framed parallel to your red line, so the wall above is parallel with the joists as well. Nothing below the wall? Seems like an ordinary partition to me.

That said - maybe there's a flush beam in the floor plenum beneath the wall? Is that a possibility? Or double/sistered joists? I'd explore those possibilities before making a call.

My general rule of thumb is - if there is ever any doubt - leave in place and do not remove.

There is no intent here to remove the existing wall.

I'm sorting through why the cracking at the door has occurred. This is the only spot where there is any visible cracking and deflections of the elevated floor framing aren't too bad. Best I can come up with right now is that something is off with the header/jamb/framing in the wall right at that location and however much truss load that the wall is taking is distressing that local area.

 

[gte447f]

The cracked gyp above the door is due to deflection of the 2nd floor framing. It doesn't really matter if that wall is load bearing or not.

Not a surprise at all seeing that the wall in question is located over a large open area below (based on the red line in your photo mark-up).

Does the wall at the right side of your red line mark-up (i.e., the wall behind the TV and fireplace) happen to align with the wall (above) at the right of the photo showing the crack (i.e., the wall with the painting and mirror)? If so, then the differential deflection of the 2nd floor framing along the length of the wall with the crack will certainly be enough to crack the gyp board.

 

[bones206]

Another possibility to consider is uplift due to truss arching. If there was a period of unusually cold weather right before the crack appeared, that is a giveaway in my experience.

I think the gravity bearing wall scenario is more likely here though, based on the shape and location of the crack. Whether it was an intentional or unintentional bearing wall, I agree with pham that it's likely acting as a "springy" support.

 

[phamENG]

It doesn't take much movement to cause a crack like that. Best bet is probably to replace the drywall in that area. A patch will just crack again. There is spackle available now with an elastomeric base that makes it more flexible, but once it's painted I question how well it'll really work.

If they want to try to "guarantee" it won't happen again...well then they need to rip open the ceiling and put in a good, stiff beam.

 

[KootK]

At 32', 2x4 chords aren't a big surprise...

It wouldn't be a big surprise in a fully triangulated truss. In an attic truss, it should come as a huge surprise.

 

[KootK]

There is one area of interest where only one end is vaulted for 12 feet and the remainder (20 ish feet) is flat ceiling and clear spans to the other exterior wall.

I could see that being a condition that draws more load towards the one interior bearing wall. This would be attenuated some by the vierendeel shear flexibility of the attic panel.

 

[TRAK.Structural]

I could see that being a condition that draws more load towards the one interior bearing wall. This would be attenuated some by the vierendeel shear flexibility of the attic panel.

View attachment 5612

Agree with this. It's another reason why I think the cracking has only occurred at this one location, its the only spot where the tributary load to the interior wall is drastically increased as compared to the rest of the wall.

 

[KootK]

Another idea for the heap. Put me down at 35% confidence.