Several years ago, Sid and I were stripping the roofing material from a leaking flat porch roof when he launched into his ritual diatribe about how little I was paying him (he was being paid as much as I was). I was just about to reply in my customary string of profanities that he should get busy with the job, when I disappeared through the roof. All that Sid had seen was the column of dust rising where I had been just a moment before. I had landed unhurt but angry on the porch floor below. When I got back on the roof, I found that a previous contractor had used Oriented Strand Board (OSB) for a section of the roof deck. It had swollen and disintegrated due to the water damage. Thus began my hatred of the use of OSB for roofs.

OSB
costs about $5-6 less per panel than plywood, which is a significant
savings when 16 or more panels may be used for a two-car garage roof,
for example. Georgia-Pacific (a major producer of OSB) states in a
2003 research paper that CDX plywood holds up better under excessive
wettings, has an all-wood surface that results in better glue
adhesion. The ‘C’
and ‘D’ are the finish ratings of the panel surfaces and the ‘X’
means it’s rated for exterior humidity.
Plywood is 15 percent lighter and flexes less than OSB.
They further state that their tests indicate that plywood holds nails
better, too. Personally, I have no problem using OSB for wall
sheathing, but I’d never use it for a walk-on roof deck and am
loathed to use it on a gable roof--especially with the snow loads
that we get in our area (the Northeast Ohio snowbelt). Several Ohio communities and several states including the state of
Florida have banned it for roof decks due to swelling caused by high
humidity along the edges.

One last thing--if you
ever do a roofing job with Sid, please smack him with a shovel for
me.
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