How To Install Z Flashing On Roof
Installing a section of siding. Installing a section of siding Skip to main content. Replacing Z-Flashing. Flashing on the top edge of each piece of plywood on a fat bead of caulk and hold it in place with just the heads of roofing nails driven into the sheathing. Don't nail through the flashing itself.
How To Install Flashing Siding
Lay asphalt, felt-paper, or special waterproof underlayment, such as a self healing membrane, over the roof. Some roofers will use 15-pound (6.8 kg) roofing paper, which is an effective method, although the best method is a self sealing membrane with a rain screen. Staple this felt down, starting at the lowest point of your roof and working upward. Overlap each row at least 3 inches. Use plenty of staples and work carefully to avoid tearing the paper. Be generous with the staples while attaching the paper to the roof deck. Use 'tin caps' under staples, if the roof may be exposed to wind before shingles are to be applied.- Use sticky back ice and water shield as underlayment where ice dams or leaf and twig dams are likely to build up, and at valleys and where the roof ends at a wall (wide metal flashing may also be used there).
- Install new flashing. Nail metal flashing called 'drip edge' along the bottom edge of the roof deck near the gutters. You will also need rake edge flashing for the sides of the roof. Make sure to install flashing around the chimneys and walls. These types of flashing are known as step flashing and turn back flashing.
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Like all flashing, Z-flashing is designed to direct the flow of water away from a penetration in the house’s exterior. Panel-type siding installs vertically on the house’s exterior walls. On a gable end, however, a second row of panels is necessary for covering the upper triangular space. Without protection, the open horizontal seam between the upper and lower rows of panels will leak, allowing water to run along the underside of the lower panels. Installing Z-flashing in this spot greatly reduces the risk of leaks.
Vertical Siding
Panel-type siding comes in 4-feet by 8-feet and 4-feet by 9-feet sheets. The long sides of the panels have interlocking lap joints that repel water when installed correctly. The 4-foot ends of the panels are blunt and butt together when a second layer of panels is necessary. This is also true for other types of vertical siding, such as board-and-batten.
Z-Flashing
True to its name, Z-flashing is a three-sided, “Z” shape metal strip that comes in 10-foot lengths. Z-flashing sells by the width of the center section of the strip, which is determined by the thickness of the siding. For example, if you’re installing 3/4-inch cement-fiber siding panels, buy 3/4-inch Z-flashing. The top fold of the flashing, which fits behind the upper siding, is the widest, and in the case of 3/4-inch Z-flashing, it's around 1.5 inches wide. The bottom fold, which covers the lip of the lower row of siding, is typically 1 inch wide.
Flashing the Seam
The bottom row of vertical siding goes on the gable end of the house first. This creates a horizontal top edge that is even with the bottom of the roof eaves. Z-flashing goes on next, with the widest fold flush against the house sheathing. The center and bottom folds cover the top width and the upper 1 inch of the siding panel. Galvanized nails hold the Z-flashing in place and should be inserted only in the top fold of the flashing, as close to the top edge as possible. Nail sparingly. One nail per four feet is sufficient. The next row of siding fits on top of the first row, leaving only the front edge of Z-flashing visible.
Tips and Considerations
The blunt ends of vertical siding panels and boards require sealing before installation. If the siding will eventually be painted, paint the ends of the siding before installing Z-flashing. If you’re going for a natual look, such as cedar board-and-batten, brush clear penetrating sealer on the ends. Feature boards are available for covering the visible edge of Z-flashing to give the exterior wall a finished look.
References (2)
About the Author
Glenda Taylor is a contractor and a full-time writer specializing in construction writing. She also enjoys writing business and finance, food and drink and pet-related articles. Her education includes marketing and a bachelor's degree in journalism from the University of Kansas.
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