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:
• Why is my roof sheathing sagging between the trusses?
• Why is granule loss a problem for an asphalt shingle roof?
• What are the mistakes to avoid when doing attic improvements?
• What causes roof shingles to curl up at corners?
• What causes shingles to buckle along a line on the roof?
• What causes leaks at a fake roof dormer?
• What causes a sagging roof ridge line?
• What causes bubble-like blisters in a built-up and gravel roof?
• Why does it cost so much more to replace a steep roof than a low slope roof?
• What is "ponding" on a flat roof?
• Is an attic required to have a light by the building code?
• How can I inspect my roof for hurricane damage?
• Why is premature curl of roof shingles a problem?
• How can I tell if a roof has more than one layer of shingles?
• What are the common problems with attic insulation?
• What is the life expectancy of an asbestos cement shingle roof?
• What's the average lifespan of a roof?
• Why is it a mistake to replace a roof and not replace its flashings?
• Why is there no attic access hatch in the house?
• What is the building code requirement for an attic access hatch, scuttle, or door?
• Does a roof with multiple layers of shingles last longer?
• What can I do to prevent roof leaks?
• Are roof trusses better than roof rafters (stick framing)?
• Why is a popped nail in a shingle roof a problem? How do I fix it?
• What are the most common problems with wood roof trusses?
• What causes a lump or dip in the roof?
• If my roof is not leaking, why does it need to be replaced?
• How can I be sure my roofing contractor got a permit?
• How many layers of roofing are allowed on a home?
• What are the dark lines running parallel to shingles on my roof?
• Can metal roofing be used on a low slope/pitch roof?
• How can I make my roof last longer?
• What are the warning signs of a dangerous attic pull-down ladder?
• How can I find out the age of a roof?
• Should I buy a house that needs a new roof?
• Should I buy a house with an old roof?
• What are those metal boxes on the roof?
• What does "lack of tab adhesion" in an asphalt shingle roof mean?
• Why do roof edges start leaking?
• Why do my dormer windows leak?
• Do home inspectors go on the roof? Do they get in the attic?
• Should I put gutters on the house?
• How much of a roof truss can I cut out to make a storage platform in the attic?
• What's the difference between an "architectural" and a regular shingle roof?
• What does a home inspector look for when examining a roof?
• Do stains on the ceiling mean the roof is leaking?
• How can I tell if the house needs a new roof?
• Why does my homeowner's insurance want a roof inspection?
• What are the hazards to avoid when going into an attic?
Visit our ROOF AND ATTIC page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.
Diagrams and Photo - TECO