Cantilevered Plywood Subfloor

Question

Cantilevered Plywood Subfloor

TTUengr51 (Structural)

(OP)

15 Feb 07 11:50

Please don't laugh, but I have a question regarding a very small cantilevered plywood subfloor. I have a condition where I have a 6" gap between my structure (wood truss) and an adjacent building. There will be an expansion joint between the two structures, but with a 6" gap, the joint material becomes very expensive. I'm hoping to cantilever the plywood subfloor out 4" to 5" so that a smaller gap to bridge exists.

The contractor is using the Advantech 3/4" subfloor material. Does anyone know of any information that is avaiilable to 1) determine whether a plywood panel is allowed to be unsupported at its edge and 2) determine the max cantilever distance.

Any help would be greatly appreciated.

Thanks

nickky (Structural) · Answer 1 · 2007-02-15 12:27:42

One thing you can do, in my opinion, is to cantilever out some 1x flat members under the plywood, side-by-side (like T&G).
This would 1)thicken the cantilevered board and 2)would give a higher moment of inertia to the section and 3)would support the edge of plywood.

MiketheEngineer (Structural) · Answer 2 · 2007-02-15 15:31:46

Is this 5'' - 6'' cantilever carrying any real loads?? Not sure I understand the arrangement.

If no loads --- make sure it is weather protected and just go with it...

TTUengr51 (Structural) · Answer 3 · 2007-02-15 15:49:33

Yeah, the plywood would rarely see loads here. It runs parallel with a corridor (in my building) and an exterior wall of a parking garage.

To give you a better idea, there's a picture at the link below:

http://home.comcast.net/~ridgetopphoto/IMG_0194_copy.jpg

CJJS (Structural) · Answer 4 · 2007-02-15 15:55:02

As long as it's not a hazard where someone could get their foot stuck in there, I wouldn't worry about it.

TTUengr51 (Structural) · Answer 5 · 2007-02-15 15:58:40

The gap has to be closed with an expansion joint materal for a fire rating. As it is now, you basically have a chimney in which fire can shoot up between the floor system and the adjacent brick/concrete wall.

My reason for cantilevering plywood would be to minimize this gap. A 6" expansion material runs about $100/LF accorinding to my contractor.

I don't think cantilevering the plywood a couple of inches is a huge deal, but I wanted to get some other thoughts on the matter...thanks everyone!

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