Plywood Cantilever 2

[JoeBaseplate]

Can roof plywood sheething be cantilevered? I have a shelter for a golf course where the arch wants to have the 3/4" plywood stick out at the edges by 24". Roof support behind the cantilever is prefab trusses @ 24" oc.

I recall to have read somewhere that you can't cantilever any grade of wood deck but I am not sure.

 

[dcarr82775]

I don't see why you can not cantilever plywood, I just don't think it will go too far and certainly not 24" with any real load. You can calculate allowable bending/shear from the NDS for various grades and thicknesses.

 

[msquared48]

The minimum construction load for this is 20 psf. With the roofing and material dead load you could be looking at 23 to 27 psf. I would be worried about the prying action at the trusses, and would want the 8 foot dimension to do the cantilevering with a 6 foot backspan, assuming the 3/4" dimension was syufficient for the loads. I would also be concerned with the tip deflection for the workers. I assume that there is no snow load to consider.

Mike McCann
MMC Engineering

 

[MiketheEngineer]

3/4'' or 1'' might possibly work - but 3/8'' is often used. Do the calcs or better yet - put overhangs on the roof trusses to support the ply.

Also, regardless of thickness, I can guarantee you that the ply will be "drooping" and look terrible in a couple of years.

 

[azcats]

"Drooping" would be my concern as well.

Any way to hide a relatively low profile (like B) metal deck in the construction to the architects satisfaction?

 

[JAE]

Just drop your top chords in the ends of the roof and use a double 3/4" screwed and glued. Provide a continuous 1x3 on the edge to form a straight line (the architect won't like the irregular and warping plywood edges)and to form a drip.

 

[ToadJones]

From experience, I wouldn't do it.
Even with a traditional fly-rafter that span seems large. '
If we had overhangs that large, we usually went with drop-gable trusses...they make for a very sturdy overhang.

Besides the strength, having 3/4" plywood hanging over by itself will look like hell, no?

 

[JoeBaseplate]

@ JAE: Actually the arch is suggesting the overhang on all sides, so I was surely going to extend truss chords where I can but I am not quite sure what to do at the end trusses. I am working on possibly using some outriggers.

 

[ToadJones]

Joe-
Google Image search "Drop Gable Truss".
Makes for a strong overhang

 

[MiketheEngineer]

2' overhang is usually no problem - obvioulsy pending loads involved. At the ends, have the truss mfr make some dropped top chord outrigger trusses. These have their top chords dropped 3.5'' or 5.5''so that you can run 2x4's or 2x6's over those chords to support the overhang....

Done all the time.