Question on 1/2" plywood sandwich wall - <Newbie>

[Spentfire]

All:

I'm building a 4x8 benroy, and I am concerned about wall strength. My design is a sandwich wall with 1/8 luan exterior, 1/2 plywood interior with cut-outs for 1/2 inch foam insulation, and a 1/8 luan interior (i.e. no "stick" bracing). Now that I've started to cut out the excess 1/2 plywood for the insulation pockets, I'm noticing considerably more flex in the 1/2 ply than I was expecting.

My question is, once I get the insulation installed and the sandwich glued up, do you think that the wall will be structurally sound enough not to flex too much? I know everyone on TNTTT says not to overbuild, but now I'm worried about underbuild and flex! Did I goof? Should I have used a 3/4 internal ply?

Any help, consolation, or anti-hyperventilation meds greatly appreciated!

Thanks!

Spentfire

[tony.latham]

I'm on my phone right now so can't link photos. I built a 4x8 Grumman teardrop with 1/2" ac skeleton, 1/8" Baltic birch on the inside and 1/4" subfloor on the outside. The rear bulkheads were mortised and the spare were set ala Fredricks method. It's plenty strong.

But I suppose it depends on how much plywood you are hogging out and your ext/int ply.

Tony

[KCStudly]

The strength comes from the skins and how far apart they are. Once glued up your wall will be almost the same as 3/4 inch ply; very strong. Just be careful handling the skeleton in the meantime.

[tony.latham]

Once glued up your wall will be almost the same as 3/4 inch ply; very strong. Just be careful handling the skeleton in the meantime.

"What he said."

I think KC is right.

TL

[dales133]

Not to mention attachment to the floor and roof spars will give it all the streth it needs

[Spentfire]

Many thanks, everybody! Sometimes you just need a little confirmation!

Best to you all

Spentfire

[daveesl77]

Mine is 5+ feet high and 10' long. Walls are 1/8" internal ply, 3/4"x3" cross joined, wood frame with solid foam in all voids, 1/8" external ply covered with 3/16" thick cedar strips. All wood framing was half-lap joined. Once walls, floor, and curve is tied together it is like a rock. I honestly believe you could roll it over and it would not be structurally damaged.

dave

[KCStudly]

I'm actually considering rolling mine over so that I can glass the bottom! ...maybe.

[aggie79]

Mine is 5+ feet high and 10' long. Walls are 1/8" internal ply, 3/4"x3" cross joined, wood frame with solid foam in all voids, 1/8" external ply covered with 3/16" thick cedar strips. All wood framing was half-lap joined. Once walls, floor, and curve is tied together it is like a rock. I honestly believe you could roll it over and it would not be structurally damaged.

dave

They roll over pretty easy if using a curved profile:



And stand on their nose if you have a flat front:

[tony.latham]

A rolling teardrop gathers no dust.