What is a Z-bar on a metal roof?
Short answer. A Z-bar, also called a Z-closure, is a strip of metal bent into a Z shape that is fastened across standing seam panels at the ridge, hip, headwall or other transitions. It seals off the panel ends with sealant underneath and gives the ridge cap or flashing something to attach to without screwing through the panels where water runs.
How it works at a ridge
- The panels stop a short distance below the ridge, and the panel ends are often bent up slightly to form a dam.
- Sealant tape or butyl is laid across the panel flats where the Z-closure will sit.
- The Z-closure is set on the sealant and fastened, sealing the opening at the top of each panel.
- The ridge cap attaches to the upper leg of the Z with rivets or stitch screws, so the cap's fasteners never pierce the panels.
The same idea is used at hips, at headwalls where a roof meets a wall above it, and at changes in roof pitch.
Why it matters
Standing seam roofs are designed to keep exposed fasteners out of the water path. The Z-closure is what makes that possible at the top of the panels. It also blocks wind-driven rain, insects and birds from entering the open panel ends.
Where Z-closures fail
- Gaps in the sealant, especially where the Z crosses each raised seam.
- Closures cut short or not notched to fit the seams.
- Fasteners placed outside the sealant line, which creates new leak points.
- Installing the Z facing the wrong direction, so water is guided in rather than out.
Other meanings of Z-bar
In metal buildings, Z-shaped steel purlins or girts are structural framing, and in siding, Z-flashing sheds water over horizontal joints and window heads. On a residential metal roof, Z-bar almost always means the closure described here.