Shakes over OSB

[fyrmnk]

Hi all. Inspected a 7 y/o home with shakes installed over solid OSB decking. I have only seen it over spaced slats before. It has had some maintenance and needs several more shakes replaced, which I wonder if that is related to the solid decking.

Cedar shake/shingle website says shakes can be on solid decking but has only been tested on plywood. Any input? Thanks. Kevin

[Brian G]

Right off the top of my head I can't imagine what would be different about OSB vs. plywood for this purpose. I do tend to prefer plywood in general.

Brian G.

[kurt]

Same here. If the shakes, felts, & fasteners are installed properly, I don't see why there would be a substantive difference between OSB & plywood.

[hausdok]

Fyrmnk,

Were you able to determine whether there is a separate layer of felt between each successive course of shakes and whether there was any type of cedar breather or battens beneath the shakes?

Re: The difference between plywood and OSB - OSB has an extremely low perm rate and actually qualifies as a vapor barrier. They perform about the same regardless. I occasionally see ply used beneath shakes here, but I've never seen them on OSB. I should think that there'd be some substantive drying issues involved with OSB, given the fact that it won't allow the deck to dry as easily as plywood will.

ONE TEAM - ONE FIGHT!!!

Mike

[kurt]

Good points. That's what I meant about "installed properly". I probably should have indicated these specifics. The primary problems I see w/ shakes are when they are installed without adequate ventilation or breathing room. They will rot from the underside when installed over impermeable surfaces, so OSB could accelerate problems if they shakes are not installed "properly".

[chrisprickett]

Try these guys for more info:

www.osbguide.com

They got back to me pretty quickly on a question I emailed to them.

[Jim Katen]

Originally posted by fyrmnk

Hi all. Inspected a 7 y/o home with shakes installed over solid OSB decking. I have only seen it over spaced slats before. It has had some maintenance and needs several more shakes replaced, which I wonder if that is related to the solid decking.

Cedar shake/shingle website says shakes can be on solid decking but has only been tested on plywood. Any input? Thanks. Kevin

The roof performs better in almost every regard when the shakes are installed on skip sheathing. (Or 'spaced slats' as you call them.)

That said, most modern shake roofs are ready for replacement after only 15 years anyway.

Any difference between plywood and OSB in this application is academic.

- Jim Katen, Oregon

[fyrmnk]

Thanks for the responses. Mike, the felt was in between each layers as needed. As far as the decking, I had for the most part only seen it on the spaced decking in this area for ventilation, that's why it kind of threw me. Thanks

[DLRambo]

Kevin - Here in Kansas City we mostly see them on skip sheathing. In St. Louis, Rolla, Topeka I often see them on OSB or plywood. Its not the 1st choice of the Cedar Shake & Shingle Bureau BUT allowed. With our typical wood roof in KC being ready for the trash can by 16 years and with the high cost compared to a good quality comp roof - you'd think someone would try to get every bit of life out of them that was possible and not use solid sheathing.