Wood Gable End
Wood Gable End
(OP)
Hello fellow eng-tippers,
I am working on the design of a 75’x75’ single-storey wood building with a gabled roof. 4 walls will be constructed to eave height followed by the 2 gable end walls (triangular walls).
I have a few questions about the gable end detail. I have attached a detail to this post for your comments.
-How can I maintain continuity of the 2 top plates (my diaphragm chord) at the ridge where the top plates will simply butt each other?
-Architectural requires a 2’ overhang – would I need to detail this or is that typically just stick built by the contractor? If so, any ideas as to how the overhang can be framed?
Thanks for your help.
I am working on the design of a 75’x75’ single-storey wood building with a gabled roof. 4 walls will be constructed to eave height followed by the 2 gable end walls (triangular walls).
I have a few questions about the gable end detail. I have attached a detail to this post for your comments.
-How can I maintain continuity of the 2 top plates (my diaphragm chord) at the ridge where the top plates will simply butt each other?
-Architectural requires a 2’ overhang – would I need to detail this or is that typically just stick built by the contractor? If so, any ideas as to how the overhang can be framed?
Thanks for your help.






RE: Wood Gable End
I would drop the double top plate of the gable end wall by 1.5" to allow the 2X4 flat material to cantilever and have a back span to the first truss beyond the gable end. Then block between the 2X4 material. This is pretty normal construction. Sometimes the first truss is dropped 1.5" too to allow a greater back span.
Mike McCann
MMC Engineering
RE: Wood Gable End
Regarding the diaphragm chord, I would use the double top plate BELOW the gable for that purpose. The sheathed gable end truss must act as a shear wall to transfer the diaphragm force down to the double top plate.
DaveAtkins
RE: Wood Gable End
DaveAtkins,
I went with the gabled wall because a gable end truss would have to transfer quite a bit of drag force. Also, the architect prefers the gable end wall.
I am having a hard time imagining how the wall plates BELOW the gable end wall can be engaged as the chords for the roof diaphragm/sheathing. Do the chords not have to be fastened directly to the diaphragm sheathing? The section as it is currently detailed now, can what you have suggested work, if so, how?
RE: Wood Gable End
Mike McCann
MMC Engineering
RE: Wood Gable End
When the structure is finished, you cannot tell the difference, so why is the Archi opposed?
RE: Wood Gable End
The only diagonals in the plane of the truss are usually at the interior trusses, not the gable end truss. The diagonals shown in the section are the diagonal struts from the bottom of the gable end truss to the roof diaphragm to laterally brace knuckle joint at the connection of the bottom chord of the gable end truss to the wall below.
Mike McCann
MMC Engineering
RE: Wood Gable End
Maybe it is different in your area. GET's here definitely have diagonals, but they are fewer in number (panel points are spaced out longer)
RE: Wood Gable End
RE: Wood Gable End
DaveAtkins
RE: Wood Gable End
I agree with AELLC that I can't see the advantage of a gable wall over a gable truss from an architectural standpoint.
As stated in some of the posts above, I agree that by sheathing the gable end truss you have addressed the drag force issue. I am in Arizona and have seen gable end trusses both with and without the diagonals depending on which truss manufacturer provides the truss.
As far as connecting the top plates at the ridge why not just use a Simpson strap applied to the top face of the top plate? I added a typical detail for this condition to the attachment. This is not really an issue if you have a gable truss.
As far as connecting the chord, which is the top plate in this example, directly to the sheathing, I would say no, you do not have to connect the chord (top plate) directly to the sheathing. At the eave walls, I assume you are going to have blocking between the trusses and you will nail the sheathing to the blocking and attach the blocking to the top plate with a Simpson A35 or RBC or toe nails. I think the top plate will still act as a chord member even though it is not directly connected to, or maybe we should say "touching", the plywood.
RE: Wood Gable End
So inexperienced engrs go thru all this mental anguish about chords and diaphragms and such.
Strictly speaking, yes (!) the chord need to be in contact and in the same plane as the diaphragm. However, in reality, an indeterminate width of roof sheathing ends up being the chord, seeing how the sheathing is nailed to the gable end truss.
So the G.E.T. detail is fine and everything works, without any way to really quantify all this. It is much easier to construct than a gabled endwall.
RE: Wood Gable End
I have one more question that I would like to pose:
If I were to make the switch to a gable end truss, I will need to rely on the truss to transfer lateral wind forces. Can the truss supplier design a gable end truss that can take 35psf of lateral wind load when the truss is 15ft deep at its peak? Seems a bit much.
RE: Wood Gable End
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