With 4x8 roof sheathing it will lay lengthwise perpendicular to the rafters trusses the grain is on the length axis.
Roof sheathing orientation.
For information on large panelized roof systems refer to the commercial construction application section.
Roof sheathing is another matter since roofs experience forces applied both parallel and perpendicular to the long direction of the plywood.
As the name implies osb has an orientation it will have arrows printed on it showing its strength axis grain.
On roofs and floors sheathing is installed perpendicular to supports because this is the orientation that results in the strongest roof or floor.
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Common roof sheathing applications and installation recommendations are described in the related publications listed at right.
The osb roof panels should be installed with the grade stamp facing into the attic and the screened surface with the nail guide lines facing up.
This solves two points of weakness.
Zip system roof sheathing general installation roof 60 panel orientation and edge spacing 60 taping 61 common details roof coverings 62 ice and water membranes 69 h clips 70 alternative details 71.
Journal of light construction december 11 1999.
The roof s sheathing helps to keep the roof trusses or rafters properly spaced and is the strength that holds.
Correct installation of roof sheathing will ensure the best performance and help reduce complaints and callbacks.
Why osb roof sheathing orientation matters.
Roof sheathing is a lot more than just flat panels onto which shingles are attached.
We could in theory credit a plywood panel installed perpendicular to the rafters with the higher shear force in that one direction but we would be forced to accept the basic code value in the opposite direction.
The main one is the structure turning into a parallelogram where the studs are no longer perpendicular to the ground.
Structural sheathing panels have a strength axis that runs parallel with the panel s length unless marked otherwise.