Garden Shed Base - treated plywood?

[jx67]

Hi There,

I am building a shed base for a plastic shed I am getting. I don't want to pour cement, so I am going to use treated wood at the bottom. I plan to put a plywood or OSB on the top of the foundation. This is not the floor of the shed, but where the plastic shed will be placed on.

I saw most people use OSB or simple exterior plywood. I went to Lowes today and the guy suggested that I need to use treated ply for this.

What do you think?

Thanks,
Joe.

[LCHIEN]

seems to me that even treated ply left in close contact with damp ground will not last very long. OSB even worse.

Does the plastic shed have a plastic floor?
Maybe a bed of gravel then the base?

[jx67]

The shed has a plastic plan. I was just worrying about the deck will rot.

I like the idea of gravel, thanks. If I do that, do you think I still need to use treated ply?

Thanks again,
Joe.

[jx67]

I should make it more clear. If the ply will not touch the soil, is there still a need to have treated ply? I am just worrying about rain/moist.

Thanks,
Joe.

[LCHIEN]

if the plastic will stand up to being trod on one side and sharp corners of the gravel on the other and not cut thru, then why use the plywood? If the plastic will be damaged then the plywood will cushion it some.

[jx67]

Yes, I am hoping to use the ply/osb to spread any weight, especially when I walk in. So, what's your take? I don't think I can use indoor ply. You think I should use ACX or BCX fly?

Thanks,
Joe.

[wardprobst]

I'd use treated if you have any wood eating bugs around.
DP

[sweensdv]

I built a base similiar to what you plan to do for use with a metal shed. I used treated lumber and ply for everything and 9 years later both the lumber and ply are still in great shape.

[dbhost]

You will want to lay and level a base of gravel first to allow for drainage and air movement, and then yes, ply would be fine. PT better than not. No matter what you use sheet goods wise, you will have rot due to close proximity to ground / moisture and not enough air space down there...

[Daryl]

Hows about rigid foam house wrap? It would be waterproof, but not sure about how it would stand up as a base for the shed.

[jx67]

I built a base similiar to what you plan to do for use with a metal shed. I used treated lumber and ply for everything and 9 years later both the lumber and ply are still in great shape.

Just to make sure, so did you use treated ply?

Here's my plan after hearing the opinions. I will have treated joists and just an OSB or an BCX ply on top, but will fill the in-between-joists space with rubber bark (had these in the area now), and also 1-2" surrounding the base. That way, I can ensure that soil is not in direct contact with the top of the base.

I am still not sure, however, which one deals with moisture better? OSB, ACX, BCX, or treated ply. I was told marine ply is the best, but I feel it is an overkill in San Jose, and frankly I don't even know where to get it.

Thanks again everyone,
Joe.

[jx67]

Hows about rigid foam house wrap? It would be waterproof, but not sure about how it would stand up as a base for the shed.

Hmm, maybe put this one then the ply? I guess in that case I can just use a soft wrap. I think the main problem is really the edge of the ply. I can use water sealer, just now sure how well it holds up.

Thanks,
Joe.

[pelligrini]

I am still not sure, however, which one deals with moisture better? OSB, ACX, BCX, or treated ply. I was told marine ply is the best, but I feel it is an overkill in San Jose, and frankly I don't even know where to get it.

The PlywoodCompany of Fort Worth has some good details on their product pages. http://www.plywoodcompany.com/applic...categoryid=145 The AC and BC are the face and back grades. I believe the X denotes exterior grade. You don't really need the better A grade for sub-flooring. Don't use OSB, it doesn't do water well at all.

Marine grade would probably be best. I think a rated sheathing would be second (type X). It's usually a C or D grade face layer with some weather resistive glue. It's not designed for long term moisture conditions though.

Treated will help resist bugs and slow rot. I used 3/4" treated ply for the front porch area for my shed/shop. The top is totally exposed to the outside, but it is not in contact with the ground. I should have used marine grade ply as it is starting to delaminate. It started delaminating after a year. The edges are warped and wrinkley and there are ridges forming in the middle now.

[leehljp]

In Japan and here in the USA in MS and AR, pressure treated ply is FAR better than non-pressure treated when it comes to insects and wood rot from underneath humidity. I just dealt with having to replace a floor in a storage unit that had PT 2x6 for joists but regular 3/4 ply for the flooring because of termites. The joists were in great shape but the termites just traveled on the PT joists to the ply and made their meal there. I had a similar problem with wood eating ants in Japan for my little shop there. PT 2X was left alone but non-PT wood flooring was eaten through within 5 years of building.


Edited: Forgot to mention - what attracts termites and other wood eating bugs is humid environments, which also causes fungus and mold. Make sure you have plenty of vents for good air circulation under neath.

[Basstracker34]

I bought a Rubbermaid Roughneck 7x7 plastic shed shed from Lowes. What we did was level the dirt ground as best we could. Build a treated 2x4 frame with aproximately 16" center joists. Then I put 3/4" plywood on top of that. Be sure to use correct fasteners approved for treated wood.

Used Lifetime's manual for plan to build it.
http://www.lifetime.com/customer-car...sheds/6418.pdf