This is not going to be a long term solution but I would like to lay some new plywood sheeting over the old floor in a wood shed. I hope to get 5 or 6 year out of it.

The shed is wood framed, about 8x12, and I would guess the joists are 2x4s sitting directly on the ground - which I know is a problem, but not one I can easily remedy.

It is about 20 years old and I am stepping through the old plywood floor in spots and my mower tires are also breaking through.

I could rip it out and fill it with gravel, but I prefer the sheeting. I plan to trim some sheets, lay them over the old sheeting and tack a 2x2 toe rail around the perimter.

The question is - what plywood would work but still be economical? Also, is there anything I could reasonably do to extend the life like apply Thompsons or something else?

I'd like to get 5 or 6 years out of it. At some point down the road I plan to replace it with a large polebarn on a concrete slab.

Pressure treated plywood. The thicker the better, I'd go at least 3/4 inch.

23/32" roof sheathing comes to mind. Yes, you could prime all six sides of it. Marine-grade plywood will hold up better; I've seen it but not locally, I know less about it, but recall it is more common where there is a lot of boating.

An elegant solution would be to rip out the floor and 2x4s and construct new floor support with 2x4 treated lumber. Let it sit on the ground, maybe slightly raised, shim with bricks as necessary. Let it float right there, not attached to the building. Leave a tiny gap around the perimeter. Secure the new deck to that.

What they call CDX 3/4" should do as well for that time.

quote:

Originally posted by PHPaul:
Pressure treated plywood. The thicker the better, I'd go at least 3/4 inch.

^^^This.

quote:

Originally posted by bigdeal:

quote:

Originally posted by PHPaul:
Pressure treated plywood. The thicker the better, I'd go at least 3/4 inch.

^^^This.

Agreed. 3/4” PT plywood.

Pressure treated, and roll on a layer of epoxy paint on top.

It’s going to deteriorate from the bottom. If you are going to coat anything do it from the bottom. But coating new pt wood is a looser. I’d put some form of barrier material between the old and new floor and call it good.

A lot of exterior small buildings get pressure treated T111 sheets. You can oil base stain in every few years and in various colors. Look up PT T111.

Ooops..did not read it was for floor.

Buy a roll of plastic to put between the old floor and the new floor. Use pressure treated plywood. Your real problem is going to be the studs rotting.

Look into marine plywood, similar to this.

https://www.lowes.com/pd/3-4-C...on-as-4-x-8/50254845

For this application and use there is no reason to spend 2x for marine plywood. Put down some plastic or another moisture barrier and have at it with PT plywood.

Roll roofing tar-paper then install 3/4" plywood

I'd use standard plywood and then seal the bottoms and sides with fiberglass resin and then put a layer of fiberglass cloth and resin on the top...… Marine plywood is a good idea also.

Something to consider is that even if you are able to install a plywood layer that has some longevity, you don't want to preserve that layer at the expense of the structure below. I think an impervious layer below the plywood like plastic sheeting, might make the structure rot faster.

I don't know what the current availability of wood preservation treatments is like due to environmental concerns, but it might be good to spray the structure and exterior plywood sheets on install. I assume treated wood will give some protection to untreated wood in contact with it, and you'll lose that if you put a barrier between them. Possilby a membrane such as house wrap could help.

Think about how you can limit moisture under the structure, such as with water diverting landscaping and gutters; Also you may be able to limit damage from moisture with ventilation, maybe with wind driven ventilators like you see on grain bins.

3/4" treated is best but I suspect for what you are asking you could get by with 5/8ths. It will probably last the 5 or 6 years you quoted....

Oh, and plywood for sure not that composite stuff...