Wood Parapet - Kicker / Shed Roof Connection Detail

[RFreund]

We are raising the parapet of a wood structure. The existing structure has near flat wood roof trusses and wood walls. The wood roof trusses are bottom chord bearing on top of the existing wood stud wall. The new parapet studs will have a short cantilever (equal to the depth of the existing truss), however, in some locations we will add kickers on the roof to brace the parapet studs (i.e. form a shed on the backside of the parapet). My question is - what is the best way to fasten the diagonal kickers to the parapet wall and the existing roof.

I have thought about fastening them alongside the existing roof trusses and along side the parapet studs. Two issues with this -> you have to cut the diaphragm to install each kicker and you interrupt sheathing on the back side of the parapet wall. I though about using a plate so the cut is smaller. I thought about putting down a double 2x member which and using a hurricane clip and toenails for shear. The problem with joist hangers is there is no rating for axial load tension.

Any suggestions are appreciated.

EIT

http://www.HowToEngineer.com

 

[Triangled]

Yea, cutting through the horizontal diaphragm is challenging as say, for reasons including subsequent waterproofing. The following idea occurs to me:
Build a triangular structure at each truss, (I'm guessing they are 24" oc or so, 96" oc may ceate a different concept), consisting of parapet stud, flat base and 45 degree brace. If you have a long run, a truss company can make these very inexpensively. Plywood up the backside and roof up the backside.

 

[RFreund]

Imagine that, Triangled wants me to use triangles

I think that is a good idea, and the direction I will head. I'm still not quite show how I will fasten it down to the roof. Possibly install a nailer which is at the back of the truss, laid flat on the roof and runs perpendicular to the new trusses. It then gets lag screwed into the existing trusses. Then the new triangle trusses will have a simpson clipangle which fastens them to the nailer.

EIT

http://www.HowToEngineer.com

 

[wannabeSE]

Be careful with the clip angles. Many of the Simpson clip angles may not have an allowable capacity for uplift at your connection. Notice the F2 only goes in one direction in the Simpson sketch below.

 

[EngineeringEric]

Why not just lay a member on the flat on the roof, nail or use rated screws into the truss top chords then toe-nail an angled kicker to the studs at say 24" o.c., sheath the slope, apply roofing membrane to all of that...? just place your member on the flat at a truss panel point, check the truss for the loads (assume sharing of the loads if you space them) and just calculate the capacity of toe nails. (4) 16d nails with a wind Cd factor should be pretty good for capacity unless you have a giant parapet....

 

[RFreund]

@wannabeSE -> very good point and I did consider this. I think the A35 has some capacity but it puts the flat member in cross grain bending. Not the end of the world in this case as it is similar to sheathing nailed to the bottom plate.

@EE -> you know I thought of toenails at first but then shied away from that; really without sound justification. I suppose that is the simplest rout and the framing is fairly redundant.

EIT

http://www.HowToEngineer.com

 

[jayrod12]

I was going to suggest the same method as Eric. It seems the easiest from a framing and waterproofing point of view.

 

[KootK]

Could the parapet studs work without kickers if they were 2x8 or 2x10? From a building envelope perspective, kickers are a last resort for me.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[wannabeSE]

If the kickers are going to be covered with sheathing, can you bevel the plate Eric suggests; nail the sheathing to the plate and kickers; and use the sheathing to transfer the tension loads between the plate and the kickers?

 

[woodman88]

Be sure to show a calculation that the existing roof trusses work for the kicker load. So that if anything happens to the trusses you can show that you checked this.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.