Originally Posted by
Richard Rushing
Hello Kenton,
Actually, the primary function of an H-clip is to provide spacing (not edge support) for the decking. The spacing is designed to allow for expansion and contraction during seasonal changes.
Now, do they provide some edge support? Sure. But that is not their primary function or design (to provide strength)... it to prevent edge buckling.
Ever seen horizontal buckling or raised sections of the roof covering... not usually. Usually it will be in the form or vertical (from drip to ridge) buckling. That's because the yahoos will sometimes butt the edges up against each other.
Rich
Rich
The primary purpose of the H clips
is to provide edge support of the panels and to stiffen the roof deck. If you use H clips (or wood blocking), then for a given panel thickness you can increase the spacing between rafters. Or for a given rafter spacing, you can use thinner sheathing. This is backed-up by the TECO references that were provided and in the building codes (IRC).
A secondary purpose of the clips is that they designed them so that they would also provide the 1/8 inch spacing (making the "nail in the rafter" technique unnecessary). The spacing is needed to protect the installed plywood from buckling if it gets wet during construction and before the roof covering is applied (or if the roof covering subsequently leaks), more-so than to account for seasonal changes (this is true for my climate -- it could be different for a hot/humid climate in the south).
Manufacturers instructions for the H clips recommend a maximum gap of 1/4 inches between panels.