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Q. Leaks at H-Clips With Zip Sheathing

We recently installed a Zip System roof over roof trusses spaced 24 inches on-center. The lumberyard told us to install H-clips as for conventional sheathing, but after taping over all the seams between panels, we found that water leaked through the tape at almost every clip. Later I heard that the H-clips weren’t needed in the first place. Are they required? And if they are, how do you prevent leaks?

A.Chris Clark, product application engineer at Huber Engineered Woods (maker of Zip System roof and wall sheathing), responds: You don’t mention what thickness Zip System sheathing you used, but the requirement for H-clips is dictated by code. Under the IBC, 1/2-inch PS-2 panels with a span rating of 32/16 can have an unsupported edge of up to 28 inches, while 5/8-inch 40/20 panels can span up to 32 inches. If you’re fastening 1/2-inch or 5/8-inch Zip System roofing panels to rafters or trusses on the typical 16-inch or 24-inch spacing, H-clips aren’t needed.

For 7/16-inch Zip System panels, Huber Engineered Woods requires panel edge support (blocking) or approved edge clips if the on-center spacing of the framing members exceeds 16 inches. Three specific edge clips have been approved by Huber for that application: the Simpson Strong-Tie PSCA7/16, the Simpson Strong-Tie PSCL7/16, and the Tamlyn PCS7/16. The use of any other brand or model clip will void all associated Zip System warranties.

In addition, it’s important to use proper technique when taping over H-clips. The tape must be centered and adequate pressure applied on all sides of the clip to ensure a reliable seal. A video on taping over H-clips is available on the Zip System website.