Cantilevered Roof Truss


SNestor
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Yes...I've searched the forum. Bill Emery posted a an answer to a post a while back with some very good info (here)...but I still have a question.

 

I can create a cantilevered truss if the overhang is short...like 16" or less. But - is it possible to get a roof truss to cantilever if the overhang is 24 or 30 inches? 

 

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1 hour ago, SNestor said:

I can create a cantilevered truss if the overhang is short...like 16" or less. But - is it possible to get a roof truss to cantilever if the overhang is 24 or 30 inches? 

Sometimes by raising the roof just an eighth of an inch will get the trust to rebuild and span across to create the soffit.

It’s a hit and miss with cantilever trusses.

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There are a few methods Steve.  You can manually modify the truss polyline, you can manually modify the truss members, or you can use the required calculations to make it happen automatically.  
 

For the latter, you can either take the necessary measurements in an elevation view and adjust the roof plane accordingly, or you can input the required numbers directly into the Build Roof dialog.  Amongst other things, the required formula depends on whether you want to use a specific overhang or a specific heel height.  I posted some macros to help speed up these calculations in another thread.  See if this helps at all...

 

...as Michael alluded to above though, the numbers need to be set just so.  I wouldn’t say it’s hit and miss, but it can definitely seem that way if your measurements and calculations aren’t precise.

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For what its worth I just did this for an as-built, 3'+/- cantilever truss..

 

I built an exterior wall, parallel and offset the distance I wanted the cantilever minus the overhang and made the wall invisible. Set the roof plane baseline to the invisible wall, built the roof plane.  That set the fascia top and ridge height spot on to the other planes. Built my trusses then I deleted the invisible walls.

 

Worked for me

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1 hour ago, Doug_N said:

Speaking of truss designs, how do you attach drywall to the ceilings in a truss construction?  How is this detailed?

Separate thread in Chat Is better, but my experience building taught me to first strap the bottom chords in steel channel, that simple cheap acoustic one, on 16" centers, and then 5/8 rock on that.  The sheetrockers throw up that  channel so fast and cover it you hardly get a chance to see it.

 

Edit: resilient channel.  https://www.ebay.com/itm/RC1-Resilient-Channel-86-lengths-32-pack-/192842078103

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1 minute ago, GeneDavis said:

Separate thread in Chat Is better, but my experience building taught me to first strap the bottom chords in steel channel, that simple cheap acoustic one, on 16" centers, and then 5/8 rock on that.  The sheetrockers throw up that  channel so fast and cover it you hardly get a chance to see it.

Gene, thanks for that info.  Good idea.

So then the resilient channel helps to prevent the cracking of the tape where the ceiling meets the wall?   I have heard that is an ongoing problem with using the bottom cord of trusses to support the ceiling.  The cord moves vertically with the varying strain on the trusses, but the walls don't move, so the ceiling to wall joints crack. 

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Some guidelines say to not fasten the last 12" of drywall, at the wall, to the bottom cord - let it "float." The drywall on the walls will support the ceiling edge and allow the trusses to move. The logic goes contrary to the way most think, but seems to work. If on an interior wall, use truss clips and fasten to allow the truss to float but still be held in position by the clips. Also, this one from JLC https://www.jlconline.com/how-to/interiors/truss-uplift-solutions#:~:text=Truss uplift usually occurs when,that closes in the summer. Another article https://inspectapedia.com/interiors/Roof_Truss_Uplift.php

 

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