How thick a sheet of plywood do I need?

[Don Morris]

I'm building a scaffolding over a stairwell to walk on while painting. I could use my extension ladder, but LOML refuses to let me do that. She's worried I'll fall off the ladder. What happened was one slipped out from under me years ago outside on a slippery deck from pollen, which acted like a lubricant. So In truth, I didn't fall off the ladder, it slipped out from under me. She doesn't care, I'm not allowed up high on ladders anymore. The scaffolding will be resting on a 2" x 12" x 10' board on one side and a 6" lip of the second floor on the other. There will be a gap of 2' between the board and the second floor for a length of 9'. The plywood then will be over a space of 2' x 9'. What thickness of plywood would I need to be safe to walk on over that space that can handle 175 lb man. I'm thinking 3/8" plywood would be minimum, 1/2" would be very safe and 3/4" would be overkill. Somehow, I just haven't had a lot of experience walking on plywood over empty space. Need someone who has...Thanks.

[James Tibbetts]

Don if my behind is on the line overkill is just right! If you go with 1/2" be sure it is 4 ply. Ther's a lot of 3 ply sheathing grade stuff out there that I wouldn't trust at all.

[Wayne Hendrix]

If that is all you are going to use it for I would buy 3/4" OSB rather than plywood. It is cheaper around here.

[Don Morris]

I saw some 3/4" OSB (or close to it) at HD yesterday while browsing. Sounds like a good idea. Thanks, LOML will be happy I don't end up in the ER again.

[Lee Schierer]

I saw some 3/4" OSB (or close to it) at HD yesterday while browsing. Sounds like a good idea. Thanks, LOML will be happy I don't end up in the ER again.

Make sure you secure some cleats on the underside so the plywood can't slip or slide off that 6" lip and add some finger holes so you can pick it up when you are finished.

[Don Morris]

Great ideas Lee, the holes for picking up will make it a lot easier...and I contribute. I actually have an automatic deduction for SMC, because the site has been such a big help. I've thought about the slipping factor as that is what brought down the ladder years ago on me. I bought some non-slip padding to go on the hard wood flooring and to protect the finish. The 2 x 12 x 10 board will be held onto the rung of a Little Giant ladder by "U" bolts at the one end and wedged between the end Post of the stair rail and the wall at the other. The OSB will be in two parts: one part will be fitted between two sides of the ladder immediately above the board and a cut out for the hand rail at the other end. The second part will also have a cut out for the hand rail and at the end of the staircase be wedged between the end rail post and the wall. I promised LOML this would be strong enough to land a helicopter on. I don't want to end up in the ER again too.

[George Bokros]

.and I contribute. I actually have an automatic deduction for SMC, because the site has been such a big help.

I would contact a moderator about the contributions to SMC. It should say "Contributor" under your name in your posts as it does under my name.

George

[Bill ThompsonNM]

I'd try the plywood on a few 4x4's or similar on the ground first. Bounce up and down and if you're comfortable, then use it. I like plywood for this application better than osb. You'll always end up with enough to build a new shop cabinet anyway.
(Or you could just rent some scaffolding)

[Patrick McCarthy]

I am with James on this one; my butt deserves overkill. Personally, minimum 5/8 but I would go 3/4. Cleats to keep it in correct space also mandatory for my sorry butt. Finger holes are excellent idea.