…… building materials: OSB .vs. plywood

[RememberGoliad]

To set the stage, we're building an outdoor bathroom, with conventional stool, shower, and lavatory. So potential for water on the floor same as in an indoor bathroom, but with the added possibility of tracking in water, mud, etc.

It will be an 8x8 room built onto the gable end of a small pole barn, with joists and T&G sheet flooring. After drying in the room, I'll somehow finish out the inside, haven't decided yet how that's going to happen, but for now I need to get it usable--dried in with some semblance of privacy--while I have some help here to do the two-person stuff.

I'm thinking painted floor for time being, with maybe ceramic or something on down the road. Gallon of paint is cheaper at sealing up wood than any other option.

All that leads up to the OSB vs plywood header. There are pluses and minuses to both. I value y'all's opinions, figured I'd ask before going and getting the materials to make it happen, probably in the next 2-3 days.

 

[Millwright]

It's OK for roof deck or maybe wall sheathing, but I wouldn't use it on a floor that's exposed to humidity coming off the ground.

 

[Border Collie Dad]

Pressure treated plywood

 

[West]

Green or PTP as said above also lay down a vaper barrier on ground first. Then try to get ventilation in space between the ground and floor joist. Insulate in-between the floor joist with the paper side of the bat insulation against the pressure treated plywood floor. At least 5/8 thick PTP if floor joist are 16" on center or greater.

 

[Publius]

It depends on the glue used in making both.

 

[dstraito]

You might try Hardie board.

Hardie Board is a fiber cement siding option composed of cement, sand and cellulose fibers. It is durable and long-lasting with classic aesthetics and is resistant to environmental factors

 

[West]

You might try Hardie board.

Hardie Board is a fiber cement siding option composed of cement, sand and cellulose fibers. It is durable and long-lasting with classic aesthetics and is resistant to environmental factors

Put the cement board on top of the PTP, for best results.

 

[mechanic 217]

Pressure treated plywood, you won't believe how much osb swells with moisture, will not use the stuff.

 

[Luddite]

Advantech brand subfloor lasts a crazy long time. Even a piece just layed out in the yard.

Cry once.

 

[Milkweed Host]

I'd go with a poured concrete floor. Less problems in the long run.

 

[blindhog]

Build a 2x4 PT frame on the ground, then PT 1x6 deck boards overlay.

 

[SNOWSQUAW]

#7 above is the winner.
OSB swells with water and then creaks! Horrible.
Ask me how I know..

 

[Macgyver]

Don't put osb anywhere the might even have the chance of getting wet.

 

[Kathy in FL]

OSB board only if you plan on having to replace every few years. We don't even using it on deck roofing anymore. Greenboard on the walls of the bathroom, even if you are going to install tile over the top of it. Hardyboard on the outside of the structure but you'll still need to keep it painted for it to last a lifetime.

 

[kyrsyan]

Pressure treated. And Mapei.

 

[223shootersc]

Pressure treated or marine grade plywood with vapor barrier or the cement board

 

[thorr]

Avantech 3/4 t&g
Pricey put do it once...

 

[Hfcomms]

Pressure treated plywood

Definitely. OSB doesn't last very long if there is any moisture involved even if you paint it to try to seal it. Expensive but you don't have to rip it out and replace it like you would the OSB. I bought a vinyl shed a number of years ago and used 2x6 trusses and OSB for the base and even though I painted it on both sides to seal it that base lasted less than five years and when I rebuilt it I used pressure treated plywood and its still looking good.

 

[RememberGoliad]

Thanks everyone for talking me out of OSB. I just about had myself talked out of it before even posting, but my wallet kept bitching at me. Y'all's responses shut that particular peanut gallery up LOL. For a number of reasons, I'm not going to go with poured concrete floor. There is plenty of ventilation under there, so I'm not worried at all about the underside of the plywood. There's other structures out here 40 years old with plain ol' T&G flooring and not quite as much ventilation underneath as this one, and it's still solid. It helps that we get almost zero rain and building on rock. I've got white pine studs that sat out on the ground for 2-3 years and are still sound. It's the water from above that has me leery of OSB--shower splash, tracking in, etc.

 

[RememberGoliad]

Hardyboard on the outside of the structure...

Gonna be galvalume, same as the pole barn it's growing off of. Only thing besides cedar T1-11 or cedar board & batten that will last 50+ years.

 

[Scrapman]

They make a high density osb sheeting that they say is good up to a year outside . Floor tile isn't that expensive for the largest size.

 

[Txkstew]

I built a 8' x 12' deck at the hunting lease for in front of my camper. It was open to the weather for at least 3 years. I built it out of 2 x 6 treated lumber, with 3/4" BC plywood for decking. I painted the plywood on all sides, including edges, with one coat of Kilz primer paint, and two coats of Walmart exterior latex paint. When I left the lease after those three years, and haven't been back, it was blistering up, and for sure going to come apart in a couple of more years. A carpenter once told me that it takes 5 coats of latex paint to get 70% seal on wood. Don't know where he got that fact from, maybe a dark wet place.

 

[Babs]

We used roof coating on the floor of our chicken coop. Seals it up against water and makes it very easy to clean.
.

 

[kyrsyan]

Thanks everyone for talking me out of OSB. I just about had myself talked out of it before even posting, but my wallet kept bitching at me. Y'all's responses shut that particular peanut gallery up LOL. For a number of reasons, I'm not going to go with poured concrete floor. There is plenty of ventilation under there, so I'm not worried at all about the underside of the plywood. There's other structures out here 40 years old with plain ol' T&G flooring and not quite as much ventilation underneath as this one, and it's still solid. It helps that we get almost zero rain and building on rock. I've got white pine studs that sat out on the ground for 2-3 years and are still sound. It's the water from above that has me leery of OSB--shower splash, tracking in, etc.

The water from above is why I said Mapei. Or Home Depot has a similar product. Expensive but worth it.

 

[Mongo]

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