I have a gable roof that was built over a flat roof in a remodel. The flat roof trusses are 2’ deep and span 24’. the gable is a simple 4/12 with 2"x8" with a RIDGE BOARD (not beam). There were no rafter ties. The rafters are attached to a plate that is attached to the trusses (ceiling trusses as well as roof truss). the plate runs perpendicular to the trusses and is attached to the trusses with structural screws. this was accepted 30 year ago by the building department. Now, I’m adding a dormer to the roof and the building department is questioning the shear properties of the design. They are not going crazy, yet, but I fee it coming. Has anyone seen this type of setup and will it pass code?
do You have any pictures ???
Unfortunately, it’s the your local building department that will decide if it passes code. I can see their concern since a dormer will add additional weight to the roof structure and the trusses. Trusses are engineered for a specific purpose and modifying a truss requires the approval of the manufacturer or a structural engineer which is probably why it was passed 30 years ago.
I recommend hiring a structural engineer.
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Thanks for asking, but I explained the situation incorrectly. The question for anyone interested is how would you retrofit a gable onto a flat roof with respect to rafter ties. You can’t really go down and connect to the wall plate. SO WE PUT A PLATE ON TOP OF THE TRUSSES (PERPENDICULAR) and attached the rafters to that plate. We used structural screws connected down to each truss with a shear rating high enough to handle the tie-force tension (1440 lbs) at the plate. Actually, I also misspoke about the City, they are not going crazy, they said they are not wedded to R802.3.1 Ceiling joist and rafter connections. (below). They just said “show me”. I just wondered if anyone has seen or done this before. thanks
Hi Martin,
If someone said that they had indeed seen it or done it before, how would that help you?
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I am with the AHJ here. Let’s see it.
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Brian, I appreciate you taking the time to respond, but there is really nothing to show. It’s just a 2x4 plate laying perpendicular to the trusses attached to said trusses with structural screws.
So, if you would, imagine you get called out for a final inspection on a gable roof that was put atop an existing flat roof (2 foot trusses; plywood and tar still afix) for “cosmetic” reasons. You immediately notice that there are no rafter ties; you go crazy on the contractor! He claims that he used structural screws to affix the plate that the bird mouthed 2x8’s are attached to. And that the screw’s shear strength is enough to handle the lateral force of the gable (meaning, the plate won’t turn up). He pleads that he couldn’t get down to the plate under the trusses, it wouldn’t make sense.
What would you say?
“Show me the engineering drawings”
The path of least resistance with a city inspector is to have a structural engineer design the dorma installation.
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