How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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What is an H-clip?
Friday, July 27, 2018
Manufacturers label them “panel edge clips,” but they are called H-clips in the construction trade because of their shape. An H-clip creates a connection point, along with a necessary 1/8” gap for expansion/contraction, between two sheets of plywood on a roof at the unsupported edges that run perpendicular to roof rafters or trusses. It should be placed at the center of the span for best results and gives the roof sheathing a little additional stiffness, because any load placed at the seam will be shared between both sheets of plywood.
They are also used for unsupported edges in plywood flooring, and building codes specify—by reference to Table R503.2.1.1(1) of the APA Engineered Wood Construction Guide—that H-clips be installed for certain combinations of plywood thickness and spans. The lack of installed H-clips is most noticeable to an inspector walking on a roof when there is a slight flexing of the roof deck under-foot because of a footstep landing on one aide of an unsupported plywood edge. However, we have never seen the lack of H-clips cause an actual structural problem, so it is not something that we report as a defect.
It is more likely that an H-clip that is damaged, jammed into the center plies of the plywood, or spaced too far from the center of the span will cause a problem—which is typically buckling or bowing due to uneven stress along the adjacent edges of the plywood. This is sometimes visible from the ground as a lump or dip in the surface of an asphalt shingle roof.
Also see our blog posts Are H-clips required by the building code for roof sheathing? and What causes a lump or dip in the roof?
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To learn more about roofs and attics, see these other blog posts:
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