Spacing between shelf brackets for 1/4 inch plywood and light load

Question

I want to put up a track around the ceiling of my basement for the cats to run around on. Looking at the scrap I have available I believe I have more than enough 1/4" plywood (dunno what kind of wood it is; probably not super high quality stuff) to make 6-8 inch-wide paths around the entire basement.

The basement walls are cinder block and/or concrete, and I have used Tapcon screws successfully in the past for other projects. I've also used these (https://www.homedepot.com/p/Everbilt-6-in-x-8-in-White-Shelf-Bracket-15418/202034287) metal shelf brackets on another project to support a cat's weight, and there have been no problems after more than a year of one of those holding up a single 8"x10"x3/4" platform.

My main question is the following -

How far apart can the brackets be to reasonably and safely support a single cat walking along the 1/4 inch plywood? Intuition says that 12 inches might be a bit overkill and 18 inches might be a bit wide. I don't have experience here, though, and I'm not an engineer.

I went looking at a sag calculator once. It indicated that I needed to place the brackets really close together if I wanted to avoid being in their "extreme sag" category when max point weight is 15 pounds (usually less). Just a few hundredths of an inch of sag would change the category from "good" to "acceptable" or "acceptable" to "extreme", and that seemed a bit tight of a tolerance to me given that I am placing practicality over aesthetics for this project.

Answer 1

"Reasonably" and "safely" aren't really at play here. Both are highly subjective.

It also depends on the type and quality of the plywood. Rough construction plywood is very different from birch underlayment with twice as many layers.

Then, it's critical to fasten it to your brackets. By eliminating the concern of sag pulling the boards off the brackets you make your installation much more robust.

So:

• Either use a good grade of plywood or double it up (staggering joints).

• Fasten to the brackets. Pop rivets might work well.

• Set up a test and decide for yourself how much movement is acceptable. You won't eliminate sag with boards that thin, even at 12" intervals. It's your call how far you span.

• At just 8" wide it'll be a noodle no matter what. Consider installing a lumber rail (could be just 2x2), and fasten the plywood on top of that. You could also float ribs between the brackets to dramatically stiffen the plywood.

Answer 2

Take your longest piece of leftover 1/4", balance it between two chairs, drop your cat in the middle and see what happens. If you don't like the result, move the chairs closer til you do.

Tack shoe boxes onto the board to make your cat a more willing partner in this exercise.