Thread: OSB Question

I inspected a new home today. The roof deck was OSB installed with no spacing. The sheets were clearly marked they were to be spaced 1/8 inch. What are the ramifications here, if any? Thanks

There is some expansion and contraction that goes on and not having any spacing can cause the touching edges to lift up or press down as they push against each other. This pressure can also cause some breakdown of the OSB material typically along the touching edges.

This can cause a wavy look to the roof surfaces but I personally have never seen anything I would call a failure of the roofing system due to a lack of spacing between the sheets of decking. Not saying its not possible, just saying that I have never personally seen it.

Thanks, Phillip. That's kinda what I figgered.

This touches on a topic that I have always been curious about... When we happen along and there is no gap how do we know that it wasn't installed with the proper gap and has expanded to fill the gap, as designed? I wonder about this when it comes to gaps above z-metal on siding as well. Personally, if I don't see bulging or some other problem I don't mention it.

Originally Posted by Greg Frazier

The sheets were clearly marked they were to be spaced 1/8 inch.

This is to be done *at the time of construction*.

As Matt said: "When we happen along and there is no gap how do we know that it wasn't installed with the proper gap and has expanded to fill the gap, as designed?"

The answer is: We don't know *how it was installed*, and its condition NOW (touching with no gap) is not a problem.

Obvious visible buckling/warping/bowing/etc., which *could be* caused by lack of spacing "at the time of installation" would be the things to look for. However, I would not report those things as "being caused by" the roof sheathing being installed without spacing as we simply DO NOT KNOW that.

Report the facts as present: the warping/buckling/bowing/etc., but I would refrain from speculating on the cause of what you are reporting.

After all, the sheathing *could have been* installed with spacing.

Good point Jerry,

If the OSB decking was installed without any spacing on a hot humid summer's day, one might even expect to find a small gap on a cold dry winter's day.

Conversely, a greater problem might be expected to visually manifest if the OSB roof decking were installed without a gap on a cold dry winter's day and subsequently viewed on a hot and humid summer's day.

had a rep from apa give a seminar on the spacing issue and he said it was a recommendation but not a mandatory requirement. they would still warranty their product without the spacing. i was suprised to hear it from one of the horse's mouth's!

Originally Posted by brian schmitt

had a rep from apa give a seminar on the spacing issue and he said it was a recommendation but not a mandatory requirement. they would still warranty their product without the spacing. i was suprised to hear it from one of the horse's mouth's!

I'm not surprised.

What warranty issues would result from lack of spacing?

Any warranty issue would result from failure of the product, delamination, falling apart, those kinds of things. Lack of spacing will not cause those types of things.

Thus, it makes perfect sense.