Gable trusses 2

[DoubleStud]

When you have prefab gable trusses, do you always use a dropped gable (last truss at the end, inside the wall, a few inches shorter to support the rake framing)? Or do you use gable shaped wall balloon framing? If you do use a dropped gable, how do you treat the big window below it. Do you assume the big window take the load from the rake framing? Or do you just put minimal header because technically the dropped gable is taking the load.

 

[phamENG]

Are you asking about handling the roof overhang, or the out of plane wind loads?

If the overhang is small and winds are low (<12" and 115mph or less), they can just attach the overhang to the face of the wall with continuous sheathing. Otherwise, a dropped gable end with a properly tied down cantilever overhang is the way to go.

If you're asking about the end wall itself, a gable end truss sitting on a wall with appropriate gable end bracing is the way to go.

 

[DoubleStud]

Thanks phamENG. This is snow country. I always do ladder framing over wall/dropped gable. Most of my projects are mostly stick framing but recently expanded my region where prefab trusses are more common. So if you have gable end truss sitting on the wall, and you have a window that is quite large, how do you design the header? Assume header will take the roof ladder framing? Or assume the end gable will take the load above the window? I just dont want to specify LVL headers unless I have to.

I will make sure to detail the bracing. Not worried about it because I will also have ceiling diaphragm.

 

[phamENG]

Header takes the load above the window, just like a stick framed end wall. Prefab truss gable ends are just stud walls turned flat and set on top of your end wall.

You should worry about it - loads during construction, inadequate fastening of drywall, roof leaks. Gable end bracing is more robust and easier to inspect.

 

[ChorasDen]

Not worried about it because I will also have ceiling diaphragm.

Careful with this one, I assume you are referring to gypsum wallboard on the bottom of the trusses, and not structural decking overtop the truss bottom chords. Gypsum board does not perform particularly well in diaphragm applications (SDPWS does not publish any design information for gypsum diaphragms). So make sure you are comfortable with that load path, if required, assuming very limited performance from the gyp.

 

[DoubleStud]

Thanks guys, I will detail my bracing.

 

[jayrod12]

In my experience, gable end trusses are anticipated to have full bearing provided across the entire length unless specifically directed to be a structural gable truss. Therefore I've always designed the window headers in those situations to support all of the loads above.

 

[DoubleStud]

Thanks jayrod12. I thought this truss will be similar to the other trusses. If the other trusses can span from wall to wall, I thought this truss will do the same. That was my rationale. I will design the long header to take the vertical load. Thanks!

 

[phamENG]

 

[bones206]

I had a recent project where I used 2x6 stud wall instead of a dropped gable end truss, because it has brick cladding and I wanted the out-of-plane stiffness for the brick backup. Here's a photo from yesterday showing how the carpenters opted to frame the end wall and 2nd to last truss as a unit on the ground before lifting the assembly into place. Not sure what to make of the upside-down joist hangers...

 

[DoubleStud]

Bones, then why not just balloon frame the end wall?

 

[phamENG]

Lumber that long is really expensive and prone to twisting.

bones - the upside joist hangers are for the unbalanced condition of a roofer hanging off the end of the overhang and praying somebody comes by with a ladder soon.

 

[DoubleStud]

Another question, what if the gable end has window into the attic? Forget about putting a truss in the wall? Too much coordination?

 

[phamENG]

Coordination isn't the issue, it's having a place to put the window. The end truss has everything turned flat so it's only 1.5" deep. Not enough to really mount a window in. And if it's livable space, not enough to insulate, either. In that case, I'd put a stud wall.

 

[bones206]

bones - the upside joist hangers are for the unbalanced condition of a roofer hanging off the end of the overhang and praying somebody comes by with a ladder soon.

Ha! Safety first! That's why they braced off the loose stack of plywood

 

[bones206]

I think having a framed wall is just more robust overall and I prefer it when the project budget allows. Provides a stiffer termination opportunity for truss bracing as well.

I don't do much residential but I only see the end trusses being used on new houses around here. Most homes seem to have the "bolt on" overhangs rather than ladder-framed outlookers over dropped trusses. I think the roof sheathing is probably doing some work helping those stay put under snow load.

 

[RontheRedneck]

Offhand I'd say one job in 500 that we do has DTC (dropped top chord) gables. They're mostly jobs that have exceptionally long rake overhangs. (Typically more than 2')

Regarding windows below gables - if I have to design a header, I figure one foot of roof load inside the wall, plus the overhang length. And add some dead load for the gable itself.

As someone mentioned, we can do structural gables. Usually nothing more than a common truss with gable studs added.

We can put a rough opening in a gable if there's a false window in it.

Someone else mentioned balloon framing walls. I've used PSL or LSL studs up to 20' long for that purpose. They're very straight and hard as a rock. My nail gun would only sink nails half way into them.

I find that gable studs often do not get braced. Alpine has a lot of gable details available on their website if anyone is interested:

https://alpineitw.com/encyclopedias/gables/