What are H-clips on roof decking, and are they required?
What they do
- Tie panel edges together: where two sheets meet between rafters, the clip keeps one edge from deflecting more than the other under foot traffic or load. That prevents the ridges and dips you sometimes see running across a roof.
- Set the gap: the clip's built-in spacer leaves about 1/8 inch between sheets so they can expand in humid weather without buckling.
- Stiffen the deck between supports so shingles lie flatter.
When code requires edge support
The IRC sheathing table lists allowable spans with and without edge support. A 3/8 inch panel rated 24/0 can span 24 inches only with edge support. A 7/16 inch panel rated 24/16 is listed for 24-inch spans either way. Edge support can be clips, solid blocking or tongue and groove panel edges. The usual pattern is one clip midway between supports, and two where the span is 48 inches.
Why builders use them anyway
Clips are inexpensive and fast to install, and in Georgia's humid climate the consistent gap helps prevent panel buckling that telegraphs through shingles. Many crews install them on every 24-inch truss roof regardless of the minimum.
During a reroof
When damaged sheets are replaced, clips should go back in where the original deck had them. Wavy lines running parallel to the eave on an older roof can point to swollen panels or missing edge support. Those lines show up clearly once the shingles are removed and the deck is exposed.