sag distances of plywood shelving

[joe zarnitz]

max. span for 3/4'' ply shelf---tks.joe

[Vaughn McMillan]

Hi Joe - You might give the Shelf Sagulator a try. You can find it here:

http://www.woodbin.com/calcs/sagulator.htm

Hope this helps -

- Vaughn

[Andy Fox]

Joe,

That varies based on width and if there's hardwood edging on the front and the expected load. Here's a general guide:

http://www.hardwood.org/display_article.asp?ID=307

Andy

[Charlie Plesums]

Since I guarantee my work, I have a simple answer. No shelves over 36 inches wide... and I do use a 1 1/2 inch face trim piece that adds stiffness. I have gone to 40 inches but at that point insist on multiple narrower bookcases (starting with 20 inch wide shelves). On the rare occasion where a wider shelf is really required (like over a large TV in an entertainment center), I either use a torsion box, or a substantial vertical support (e.g. a 6 inch vertical "back" of the shelf).

The other rule... no more than 5 feet of adjustable shelves (vertically)... I require a fixed shelf in the middle (often at the 30 inch point) of tall bookcases.

[Rob Blaustein]

This issue came up in a related post a few months ago and I looked up an article I recalled. Here is what I said back then:

"In the Spring '05 issue of Woodworking Mag they tested deflection of different combinations of span, thickness, and depth of shelves by looking at the amount of weight needed to cause the boards to deflect by 1/4". For example, for a 12" wide board, 3/4" thick with a span of 36":
-solid maple, pecan or red oak will deflect 1/4" with 313 lbs
-birch faced plywood veneer core will take only 129 lbs.
Adding a 3/4" edge of solid wood will improve the strength of the plywood (or MDF or particleboard) considerably and make it almost as strong as solid wood, especially if it is 3/4" by 1 1/2", but hardwood is still stronger.

I remember seeing a test in Wood mag some time in the past few years and I think the results were similar."

-Rob