When from the outside of a house, with what's touted to be a "completely new roof," you can see dips between the defined lines of the trusses every 2', the report can only say, "sheathing panels not in plane."
Roof sheathing is not as strong as it used to be. It used to be plywood, and thicker than it is now.
What we most often see now is Oriented Strand Board (OSB), used where Fire Retardant Treated Plywood is not.
What almost always I see used for roofs is OSB, and 17/32" thick. That is just a hair over 1/2" thick.
OSB is not as strong as plywood. It acts differently than plywood too, in that it will expand and contract more, especially swelling with heat and humidity.
As such, it needs support between the trusses. And the panels need to be separated somewhat so they don't rub one to another.
How is that done? With clips.
These clips do two things.
They provide a surprising amount of support to the panels between the trusses.
And, importantly, they separate the panels one to another by 1/8".
This allows for swelling and prevents the panels from rubbing against each other.
It is important that these clips be added when roof sheathing is replaced. When they are not present sagging can be the result.
So, when I saw sagging on the outside of this house, I predicted what we would see from inside the attic.
And we did.
All over the roof there were sheathing panels not in plane.
And they used plywood, which is typically stronger than OSB!
You can see the edge of one sheathing member highlighted by my flashlight.
And they used nails that are properly long.
So why not use the clips?
Unknown.
The code does require a minimum thickness for sheathing. But the code does not REQUIRE the use of clips.
Why? Because clips are not load rated. They do demonstrably increase stiffness between trusses however. And this study suggests that between 24" on center trusses, it increases the psi rating by 190 pounds.
I EXPECT THEY ARE NOT USED HERE SIMPLY BECAUSE THEY ARE NOT REQUIRED BY CODE.
But again, why not use the clips? It might not be required to use them, BUT IT CERTAINLY IS BEST PRACTICE.
I might answer my own question as to why they are not used. Because the job becomes quicker and cheaper?
MAYBE, BUT MINIMALLY SO!
My recommendation: a roof is intended to last a long time. So why not utilize every best practice when putting one up? Look to make sure your roof is set up for the long haul. The next hefty snow fall might prove the difference!
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