Plywood or OSB?

[jrbridges]

Does anyone know if there are issues with using OSB wood sheathing as opposed to traditional plywood for the roof of a sugarhouse?. The price is 50% cheaper. My cupola seems like it will work well (sugarhouse in construction now) but the moisture inside the building may be bad for the OSB. Or maybe it won't. I'm just not sure. I will be putting tarpaper and a metal roof over the sheathing. Any comments would be helpful.

[tuckermtn]

I would be nervous about OSB and all that moisture- but having said that, they do make exterior grade OSB.

Solid wood siding/roof planking, like ship-lap or T + G pine gets my vote as I don't trust the glues in OSB or plywood.

I get a lot of my pine ship-lap from a local pine mill that has what they call "planer-outs" basically their seconds- very cheap...

where are you in central mass? any pine mills nearby?

my .02 worth

[3rdgen.maple]

Personaly I would not use it on the roof. Especially if you do not have a steam hood. I think the 5o% less will cost you in the long run. If you are trying to cut cost a little you can skip the sheating all together and just run some 2x4's or 1 x planking say every 16 inches and screw the metal roofing to that. That is how we bult ours 20 years ago and it is still standing strong. Some like the full decking cause of the claim of it not dripping. But I think most of the steam on mine runs down the roofing instead of of dripping wherever. I would also have to think that the decking absorbing all the moisture will affect the length of its life span. I have been wrong before but that is my personal experience on this one.

[Thad Blaisdell]

At Home Depot you can buy Advantec plywood for less than $17 a sheet right now. That is a 3/4" plywood that is guaranteed waterpoof. It is made for roofing and will not absorb any moisture. A little more money than regular OSB but you will never have to worry about it.

[KenWP]

I was the oringinal tester for OSB before it became available to the public many years ago. The fellow I bought this place from sheeted in the floor of the office in the greenhouse believe it or not with the crap.I have to replace the floor this winter because I am tired of falling thru the stuff. It's just fine for garages and other dry areas but with moisture it just dosn't hold up.I paid a $250 000 bill that proves what kind if crap it is.

[petersp22]

OSB is different from the chipboard used 20-30 years ago. It is engineered and manufactured for exterior sheathing. I got my materials from a small town lumberyard where I get advice right from the owner. He told me to use OSB. I've seen it exposed for long periods of time on construction sites without apparent issues.

[The Birdman]

I would run 2x4 on 2ft centers and use foam board under metal. Metal roofs will drip alot with out any thing under it. with using 2x4 you can set your trusses on 4ft centers if you use them on edge you can go 8ft center on trusses

[HHM-07]

I used 10" rough hemlock on mine seems to work very well and very expensive, if you are in an area with lots of snowfall it makes a good rugid roof

Dick

[Sugarmaker]

I would recommend plywood rather than OSB, I am seeing some darkening on the underside of the OSB in the wood shed are of the sugarhouse. Probably from escaping steam and heat. The plywood in the evaporator room looks as good as new and it sees a lot more steam and heat. We do have hoods and to remove 90% of the steam for the room.

Regards,
Chris

[gmcooper]

We are in the construction business and have been for 4 generations. OSB is crap no question about and whether they want to call it exterior or not it will not hold up to moisture. We just finished a job of stripping off all the cedar siding on a house that was 8 years old. Problem was the OSB the builder used totally disintagrated anywhere moisture got behind the siding (the moisture wicked thru the OSB in all directions). The builder installed everything to manufacturer specs. You could actually poke your hand thru the OSB and pull it out by the handfull. Mold grows nicely once it starts to fail. The manufacuters are well aware of the issue but they will not admit any responsibilty or liability. There are multiple suits against them. Building material suppliers continue to sell it because it is cheap and if they don't sell it some one else will. The Zip system product is esentially OSB with a protective membrane applied to one side. Any cut edges or nail holes will give the same result as plain OSB. Advanteck is more moisture resistant due to the adhesive used. A bit different than OSB but about the same price as cdx fir plywood.

With a sugarhouse roof you have moisture issues from evaporator below and condesation from the metal above. Use about anything else but OSB.

[3rdgen.maple]

you would be hard pressed to find any new construction around here where the house is not sheated with osb. Of course they house wrap it after for moisture issues. I often wondered if the cost of the osb and then the vapor barrier ends up being cheaper or not.

[KenWP]

You have to put a vapor barrier with plywood also anyways. That or have windows with a inch of ice all winter and soggy insulation. The first OSB made in western Canada was tested by me and we had fun. I figured it was neat to use as it came in 16 x5 foot sheets. We sheeted in the floors of mobile homeswith it. The glue for the flooring reacted with the glue in the OSB and every joint in the floor used to cause a bubble. Cost $250,000 to fix that neat trick. Then they got the neat idea to use flat sided sheets instead of T&G and the inspectors had us screw blocks of wood under every joint to stop flexing. This was considered cheaper for some stupid reason.
OSB is cheap for a reason besides useing crap trees.

[Haynes Forest Products]

What I like about OSB is after installing 3/4" on the walls in the evap room after 18 years I ended up with 1":o

[jrbridges]

I am happy to say that all of my plywood went up today. I took many people's advice and did not go with OSB. I got some 4 ply fir, 7/16 inch and it should be good for many, many years. Thanks to all who weighed in.

[Slatebelt*Pa*Tapper]

How about painting the side of the osb that is exposed to the inside of the evaporator room, of course this takes more time to paint them and not sure what type of paint you'd use.
i have a few chicken houses/coops built some going on 8 years old, the outside of the osb is painted and exposed to the elements, wood is still in excellent condition as of today.

[Haynes Forest Products]

My shack is painted with gloss white on the inside and it is 19 years old looks better than me:mad: ...............ITS OSB :)

[red maples]

as long as its painted your all set. other wise you might melt:o

[adk1]

If you dont have a budget..Plywood, if you do, then......

[Woodland Acres]

My sugar house is all OSB ,sidewalls and roof. I have not had a problem with mold moisture or swelling.I have had steam so heavy you could not see across it. You need to put felt paper between the OSB and roofing and siding material. I have worked in construction business for 30 plus years and only issue i have seen is when it comes in contact with a water source it will fall apart.I have seen it stained on storage buildings and they are 20 years old.