Scissor truss question

[mm08822]

Isn't the rake framing lumber supposed to sit on top of and straddle the top plate of the gable? Otherwise it will sag over time.....
Like this: vs.

The difference in framing required for the rake would eliminate the use of of the current gable truss. And wouldn't the uplift on the second truss by the rake require it to be differently designed?

 

[mm08822]

When they sell you the roof trusses, they want to sell you the false trusses on the gable ends. This is helpful in that it shortens the span for your 2x studs under wind load, but you must brace the hinge in the wall. The alternative is to use full-height studs with proper connection to the lookouts and to the roof diaphragm.

Did the struss mfr know the endwall/gable had no partitions inside?
Did they know there was a rake being added?

Or were they just given a span, interior/exterior pitches, lookout/soffit dimensions?

 

[bob smith1]

Isn't the rake framing lumber supposed to sit on top of and straddle the top plate of the gable? Otherwise it will sag over time.....
Like this: vs.

The difference in framing required for the rake would eliminate the use of of the current gable truss. And wouldn't the uplift on the second truss by the rake require it to be differently designed?Your

Your pic is not a roof truss design, but correct on the overhang detail I was going to ignore. We would spec a "drop chord truss" for this. However, I thought this was a building, not a home. The crappy "way we usually do it" in these builds has to do with speed, not performance. That gable area is weak, but I also don't know the load design criteria either. We have serious wind so design for that.

 

[mm08822]

Your pic is not a roof truss design, but correct on the overhang detail I was going to ignore. We would spec a "drop chord truss" for this. However, I thought this was a building, not a home. The crappy "way we usually do it" in these builds has to do with speed, not performance. That gable area is weak, but I also don't know the load design criteria either. We have serious wind so design for that.

I know it isn't a truss design but rather the needed framing for hinge elimination and proper rake support.

A drop truss still would make for a weak design.

What difference does the type of building matter? Wind dont care.

My point was the OP now has a second reason to rework gable framing....both gables.

Even a third reason....the second truss was fabbed wrong by mfr. Take this gable truss and put it in the place of the second truss.

 

[bob smith1]

I know it isn't a truss design but rather the needed framing for hinge elimination and proper rake support.

A drop truss still would make for a weak design.

What difference does the type of building matter? Wind dont care.

Do explain......I'll wait.

 

[mm08822]

Do explain......I'll wait.

A drop truss all by itself does not remove a hinge point that has been the primary topic of this thread.

Sure there can be 2x bracing between the lower cords of multiple trusses and even upper cords (depending upon roofing material). Sheet rock alone aint gonna cut it and there may be nothing applied to the bottom chords. Really has to be engineered and built in its entirety as a full assembly.

Why build in a demonstrated weakness that has to be compensated for with additional lumber and hardware=cost+time? Just frame the gable wall straight up to the rafters from the bottom plate.

 

[bob smith1]

A drop truss all by itself does not remove a hinge point that has been the primary topic of this thread.

Sure there can be 2x bracing between the lower cords of multiple trusses and even upper cords (depending upon roofing material). Sheet rock alone aint gonna cut it and there may be nothing applied to the bottom chords. Really has to be engineered and built in its entirety as a full assembly.

Why build in a demonstrated weakness that has to be compensated for with additional lumber and hardware=cost+time? Just frame the gable wall straight up to the rafters from the bottom plate.

A drop chord truss is specific to optimizing strength for overhangs. People love to only examine bearing, like you mentioning sag. I have to analyze uplift, in which those stupid attachments have no ability to resist that, and I'm probably the only one here that does roof analysis to know the corners are HOT in uplift.

As for a hinge issue, there ain't one if you are adding a ceiling with proper bracing! It's not always about how to optimize the structure as it is who will build it. People are fabricating a condition that won't exist in a house build with bracing. Now in an open ceiling, you bet!

But here again we are, with no design load criteria to even know how to design this.