Roof Sheathing Orientation

This solves two points of weakness.

Roof sheathing orientation.

The same policy goes for roof sheathing as for hanging drywall you get more strength by spanning more rafters joists studs and offsetting the joints. On roofs and floors sheathing is installed perpendicular to supports because this is the orientation that results in the strongest roof or floor. With 4x8 roof sheathing it will lay lengthwise perpendicular to the rafters trusses the grain is on the length axis. The roof s sheathing helps to keep the roof trusses or rafters properly spaced and is the strength that holds.

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. The main one is the structure turning into a parallelogram where the studs are no longer perpendicular to the ground. 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. 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.

Roof sheathing is another matter since roofs experience forces applied both parallel and perpendicular to the long direction of the plywood. Why osb roof sheathing orientation matters. For information on large panelized roof systems refer to the commercial construction application section. Structurally it doesn t make a difference but if the grade stamp faces up it will be covered by the roofing material and the building inspector will not be able to confirm the right osb panel has been used for that application.

Journal of light construction december 11 1999. Roof sheathing is a lot more than just flat panels onto which shingles are attached. Structural sheathing panels have a strength axis that runs parallel with the panel s length unless marked otherwise. If used for floor or roof sheathing where the primary purpose is to carry loads perpendicular to the face of the sheets then it must be placed with the long direction of the sheets perpendicular to the supporting joists or rafters.

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