Plywood shelves - Will they sag over ~38" Span -- Items to be on shelves are clothing

[George Bokros]

I am building a closet organizer and will have some 3/4" plywood shelves spanning ~38". They will be only supported on the ends. Items to store will all be clothing, sweaters shirts etc., will the shelves sag over time. The shelves will be either be faced with a 3/4" piece of solid wood or veneer so not much support from the facing.

Thoughts, opinion??

Thanks

[Dan Hulbert]

Do a google search on "Sagulator". Plug in your materials and dimensions, and it will give you a good idea of how much sag to expect.

[Jamie Buxton]

If you don't like the answers you get from sagulator, you might look for 1" plywood. Dealers in my area stock 1" maple-veneer plywood, and 25 mm baltic birch. The shelf stiffness goes up as the cube of the thickness, so 1" sags half as much as 3/4".

[Peter Quinn]

Yes, they will sag. They make metal T stiffeners that you can route into the front and rear edges to span that distance then cover with edge banding or you can go with thicker shelves, or add solid edges. Depending on the depth you could use 1/2" plywood backs and add pins or magic wire at the mid span, or hang the shelves on z clips which will minimize sag at the front by fully supporting the rear. But with no support mid span I predict sag.

[Wade Lippman]

Can't you add some extra material at the back on the bottom?

[Jerome Stanek]

We always cleated the back and sides

[Leo Graywacz]

Yes they will, but it's a closet...

Put a cleat on the back wall that spans the distance and glue a 1 1/2" board on the front of the shelf. This will resist sagging for quite some time.

[Phil Thien]

I don't think you're going to see much sag with clothes. Most plywood is a little curvy, so if you can, use your pieces crown-up and I think you'll be fine. Sometimes you can't crown-up because you want to be consistent in the plywood face you're showing, but sometimes it doesn't matter.

[Phil Thien]

Yes they will, but it's a closet...

Put a cleat on the back wall that spans the distance and glue a 1 1/2" board on the front of the shelf. This will resist sagging for quite some time.

Yeah that would work well. And you can hold the cleat back from the front edge an inch or two if you don't want to make the shelf look thicker. I've even seen guys paint/stain the clear a much darker color and it becomes all but invisible.

[Mike Heidrick]

I have 36" wide X 18" deep red oak 3/4" ply shelves with a 1" front hardwood edge and no sag and they are full of books.

[Leo Graywacz]

If you put the edging on the front side of the plywood you have the choice of putting it up or down. If you want a lip to keep stuff from falling off you put it up. If not, you put it down.

What's wrong with the shelving looking a bit beefier? I guess it's just a personal preference.

[John Lankers]

I have 36" wide X 18" deep red oak 3/4" ply shelves with a 1" front hardwood edge and no sag and they are full of books.

And with a beveled or rounded over edge it would give it a more high end finished look.

[Kent A Bathurst]

....... Items to store will all be clothing, sweaters shirts........

George -

Life Lessons Learned -

Your crystal ball cannot possibly be that accurate, absent a TARDIS in your basement. A little extra work - cleat on the wall in back, 1-1/2" hardwood face in front - will obviate all future head slaps.

[Warren Lake]

you can glue a strip of wood an inch or two back from the front edge and even preload it a bit with a crown by gluing it upside down and support it at each ends and put a bit of weight on it. On some stuff maybe long table surfaces only supported by the ends ive done preloads with a larger strip and lamelloed so it was like the back of a transport truck when you see them unloaded and they are up in the middle.

[Peter Quinn]

Easy enough to test. Cut a piece of plywood, put a 2X2 or similar perpendicular to the length at each end, and put some weight in the middle. See how it behaves. It really doesn't take much weight to introduce a little bow. Will you really notice it in use? Does it matter? Perhaps not, probably not going to get the kind of critical failure like with a cheap partial board book shelf where they sag so much they fall off the shelf pins, but I'd be pretty surprised if 3/4" plywood over that span didn't deflect at all.

Want to really solve the problem? I made my son a bookcase that I just recently gave him, one adjustable shelf......made my own lumber core plywood....used white oak stickers (flooring scraps) oriented to be quarter sawn, skinned it with shop sawn 1/8" maple veneers and a maple front edge. It has stayed dead flat in the 3 years the piece was in my shop, overall thickness is 1" because I could control that making my own lumber core. Its really ridiculous overkill, you could probably store a truck transmission on it without deflection, I made it that way to try out some techniques with the vacuum bag.

Frankly I prefer solid shelves if the span is any question. 4/4 soft maple runs around $3/bf around here, a decent sheet of 3/4" cabinet grade maple is $75, which equals $2.35/sf, so solid shelves are actually very competitive with plywood, bit more work involved obviously, but they hold a heck of a lot more weight than any similarly sized engineered product. Or you may be able to order lumber core plywood, though IIR that was well over $100/sheet last time I enquired.

[Robert Engel]

I think you get the idea....

....if you're still there, that is.

[Jim Dwight]

Sagulator says that 3/4 fir plywood, 38 inches long, 12 inches wide will sag 0.04 inches with a load of 10 lbs per foot. That is my conservative estimate for clothing. I don't think 0.04 inches is much. It's less than 1/16. I don't think it needs edging. If the load is heavier, maybe.

[Leo Graywacz]

Over time it will sag more.

[paul cottingham]

Groove the plywood. Route a tounge on the wood you are using as a stiffener. Roundover top and bittom, if you like that look. I doubt the resulting shelf will ever, ever sag.

[Mike Henderson]

I had a similar problem. I have a couple of closets that hold household items - heavy things like dishes. I bought some aluminum angle iron from Home Depot and put it on the front and back of the shelves.

You can barely see the angle iron on the front of the shelf in the picture. It's the same in back. The "angle" part goes under the shelf. Anyway, no sagging.

320509

If I recall, the shelves are 3/4" Baltic birch.

Mike

[Allan Speers]

Over time it will sag more.


This. Believe me, I know for sure!

- I'm never going to use plywood for shelves again.

[Phil Thien]

I've never experienced plywood sagging more over time.

MDF and particle board yes. Plywood, no.

[Bill Neely]

Yes, they will sag. They make metal T stiffeners that you can route into the front and rear edges to span that distance then cover with edge banding or you can go with thicker shelves, or add solid edges. Depending on the depth you could use 1/2" plywood backs and add pins or magic wire at the mid span, or hang the shelves on z clips which will minimize sag at the front by fully supporting the rear. But with no support mid span I predict sag.

Peter, Can you be more specific about the edge stiffeners, I'd like to take a look at them.

Thanks

[Allan Speers]

Peter, Can you be more specific about the edge stiffeners, I'd like to take a look at them.

Thanks

I made a bunch of 48" plywood shelves, and as they were getting lower and lower each month, I finally took them down, routed the front edges, and glued-in 1" steel L-channel. This, combined with the backs being glued in place, keeps them nice and level. - but it sure cost a lot. :(

Next time I'll use Oak, or at least Pine. ANYTHING but plywood.