Shed Flooring???

[crabjoe]

If you've read other threads I've posted, you know I'm going to raise a shed and my plan was to use 3/4" plywood for the flooring, but now I need to know what you think of OSB.

I have a friend in the build trade and he was able to get me 3/4" T&G OSB flooring. He feels it will be fine, and possibly better then using plywood. So now I need to know what others feel.

Is OSB just as good or better then plywood for a shed floor? The shed will be on Skids over gravel. If it's not the same or better then using plywood, can I use a water sealer like Thompsons to get it to where I need it? I just hate the idea of not using it, when it's free, but I won't if it will not do.

Thanks!!

[HayZee518]

the OSB would be fine as long as moisture doesn't get to it. the glues used in its manufacture are basically latex based and they use pressure to form the sheets. Once moisture gets to it, it expands and gets crumbly.Quite possible if you coat both sides with an oil based paint first it'll be ok. maybe even lay some poly over the joists before laying down the OSB. leave some space [1/8th inch] to allow for expansion even if you are using tongue n groove.

[pushkins]

Free is always a good thing !!...(ok almost always, this friend doesn't need you help hold trusses on a 5 story building in return does he?....lol).
Around here code says that anything that is that close to the ground must be treated.
If it were me and my shed I'd use treated ply, moisture comes in from everywhere from lawn tractors to wet boots to a 3000 tractor (yes I'm jealous)
BUT
it is free and if you treat it like Hayzee suggested with a good quality sealer (only oil based) you should be OK, Be very careful painting the tongue and groove, there is very little room here for anything extra in the fit.
The only hesitation I would have is the underside, you cannot get to it to repaint it and it's inches from the rock, might be a good idea to lay tar paper (roofing felt) over the entire floor joist system before laying the OSB.
I think using plastic this close to the OSB might sweat and cause you more problems
Being this close also might make the OSB an attractive chew toy for rodents, they tend to like OSB over treated material.

[crabjoe]

Thanks all.

I went ahead a picked up 6mil plastic to put between the joints and flooring. I'm going to go a pick up some oil based paint to put on the bottoms of the OSB too. Then on top, I'm use Thompsons water sealer. I hope I won't need to replace this later...

BTW, he's getting me pretty much all the wood I need. All I need to do is supply all the pressure treated lumber, hardware, siding and shingles. He's saving me a fortune!!

[crabjoe]

Guys, do you think it would be better to seal with an oil based paint or an oil based primer like Kilz?

[pushkins]

Use both if possible, but as a minimum use an oil based primer at least.

[mrcaptainbob]

Polyfilm

Would it be better to lay the visquean on the rock first, then build from skids on up? Am wondering if screened vents would help airflow through a sort of 'crawl' space between the skids. If any moisture did get there it has a way out. If it's directly beneath the OSB or plywood it could hold a puddle....any thoughts?

[crabjoe]

Here's my plan.. I'm going to lay down 6mil plastic on the dirt, add 4 inches of stone on them, then 4x4 skid on that. On top of the skid will be the floor joists. Between the OSB and the joists will be a layer of Kilz Oil based primer and 6mil plastic.

When I was at Home Depot today, they had a shed on skid there with OSB flooring. The OSB looked to be bare on the bottom, but it was painted gray on top. The gray paint looked like Dry Lok.

So now I figure, if there are shed builders using OSB without anything coating the ground side OSB flooring, I should be fine with the vapor barrier and oil based primer sandwiched between the OSB and joists.