What's the Difference: Ledger Flashing - Fine Homebuilding Article
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What's the Difference: Ledger Flashing

Click to enlarge image Photo by: John Ross
Proper flashing of a deck ledger is crucial to preventing water from getting behind the ledger and damaging it and the sheathing underneath, a key cause of premature deck failure. Ledgers can be flashed with many materials. Among the most common are copper, vinyl, galvanized steel, stainless steel, and aluminum, although not all of these are easy to find in all locations. FHB editorial adviser Mike Guertin, an expert deck builder, says that all these materials can flash a deck ledger adequately. “The design and installation of the flashing material are more important than the material when it comes to successful durability,” he explains. Installing one of these materials correctly, however, requires knowing what makes it different from the rest. All except for stainless steel and copper are available in both rolls and factory-bent panels. Rolled products are best bent on a sheet-metal brake.

This traditional flashing material is durable and compatible with CA- and ACQ-treated lumber. It is expensive, however. At least two manufacturers sell flashing with a sheet of copper on one side and a sheet of polypropylene on the other. Not only is it a good bit cheaper ($45 to $68 for a 12-in. by 20-ft. roll) than straight copper, but it also can be formed by hand.
14-in. by 10-ft. roll: $110

Vinyl lasts indefinitely and won’t dent. If treated with a UV inhibitor, it also resists fading and cracking. As with other vinyl products, vinyl flashing moves with changes in temperature. To accommodate this movement, cut slotted holes for fasteners (stainless steel or hot-dipped galvanized) if they’re not already there, and nail the fasteners loosely. Vinyl flashing is generally available in white and tan.
14-in. by 30-ft. roll: $20 15⁄8-in. by 8-ft. panel: $10

Galvanized Steel
Using a peel-and-stick membrane is a good idea with galvanized-steel flashing, whose zinc-covered surface degrades over time, especially in coastal environments. Frequent application of rock salt and certain other deicing chemicals on a deck also can speed up corrosion. For the best protection, choose G185 galvanized steel, which has 1.85 oz. of zinc coating per sq. ft.
14 in. by 25 ft. roll: $19 15⁄8-in. by 8-ft. panel: $20

Stainless Steel
Stainless steel is Guertin’s favorite material for flashing deck ledgers. In his coastal New England environment, stainless steel holds up very well on homes near salt water. It does the same on decks that receive salt during the winter to melt ice.
15⁄8-in. by 8-ft. panel: $30

Aluminum was the most common flashing material until CA and ACQ replaced CCA for treating lumber. Both chemicals contain more copper than CCA, which means that they corrode aluminum flashing. Separating the aluminum from the lumber with a peel-and-stick membrane is one way around this problem, but it adds a step to the installation process, not to mention an additional cost. Still, aluminum is inexpensive and readily available, so for some builders, particularly those in regions that receive little rainfall, this extra step may be worth it.
14-in. by 10-ft. roll: $6.50 15⁄8-in. by 8-ft. panel (painted): $21

From Fine Homebuilding228 , pp. 34
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