Long Live the Ledger Preventing Deck Failure and Extending the Life of a Deck

By Dave Kile

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WORKMANSHIP and wayward water are two of the biggest threats to a deck’s longevity. Unfortunately, those dangers often intersect at the ledger board, which anchors the deck to the building. It happens because builders either neglect to install ledger flashing or settle for substandard methods, such as caulking. Without adequate protection against water infiltration, the ledger traps moisture and rots. The rim joist is also in jeopardy of rot. As a result, the risk of catastrophic deck failure increases. It’s a more common occurrence than many people know—and very avoidable.

Building code requirements

The requirements for deck flashing are outlined in section R703.4 of the International Residential Code (IRC). It calls for flashing “where exterior porches, decks, or stairs attach to a wall or floor assembly of wood-frame construction.” The flashing must be “approved corrosion-resistant flashing” that is “applied shingle-fashion in a manner to prevent entry of water into the wall cavity.” The flashing must also “extend to the surface of the exterior wall finish.” Using this general guidance, it’s up to the builder to select the appropriate deck flashing materials and methods.

Flashing options – pros and cons

Code-compliant flashing materials include aluminum, galvanized steel, stainless steel, copper, vinyl, and self-adhered membranes that comply with AAMA 711. While copper pairs well with pressure-treated lumber, it can react with (corrode) galvanized steel fasteners and hardware. Stainless steel is an inert (nonreactive) flashing material, but costs more than other options. Aluminum and galvanized steel are the least expensive metal flashing options and the most widely available.

Common metal flashing is typically shaped like an “L” or “Z,” with the wall-side leg tall enough to slip under the building’s water-resistive barrier (WRB)— usually house wrap or felt—and the siding. The horizontal lower leg caps the ledger and, in the case of Z flashing, extends down the ledger face about half an inch. The American Wood Council recommends using “L” flashing that extends beyond the joist hangers. See Figure 14 in “Design for Code Acceptance No. 6 (DCA6), Prescriptive Residential Wood Deck Construction Guide.”

One common complaint about metal flashing is that it requires bending, which can be time consuming and potentially dangerous due to the sharp edges. Metal also requires nails or screws for installation, which creates opportunities for moisture penetration. While it may divert water away, it doesn’t seal water out. Moisture can still find its way to the wood and migrate to the building walls through nail holes. With that moisture comes rot and decay. Plus, aluminum and galvanized steel flashing corrode faster when they’re in contact with pressure-treated wood.

While the IRC is silent on accelerated corrosion, some building authorities restrict the use of these metal flashings because they are so prone to leaks. The common work-around is to install a membrane barrier between the metal flashing and the pressure-treated wood. But the better solution is to omit the metal flashing and apply a flexible self-adhered membrane instead. It’s an approach that more builders are adopting since new and better flashing membranes have reached the market.

Advantages of flashing tape

Of all the flashing options available, only flashing tapes have the ability to create a waterproof seal around the ledger board. Self-adhered flashing membranes also eliminate the need for mechanical fasteners that create holes, and they don’t corrode. Membrane flashing might cost a bit more than aluminum or galvanized steel, but it protects the ledger better and is much less expensive than copper and stainless steel.

The primary types of self-adhered membranes used as deck flashing are asphalt-based, acrylic, and butyl-based.

• Asphalt-based membranes. Originally used as an ice and water shield on roofs, this peel-and-stick underlayment is now also sold as deck flashing. It’s fairly inexpensive, but tends to ooze excessively in hot weather. It’s also difficult to handle without making a mess and doesn’t adhere well in cold weather. Brand names include WiseWrap and Vycor Deck Protector.

• Acrylic membranes. This type of membrane is thin, stays flexible in cold weather, tears by hand, and unsticks easily if you make a mistake. It’s also the most expensive of the self-adhered membranes and isn’t readily available in sizes or formats conducive to ledger flashing. Plus, it needs 24 to 72 hours to fully set. Nichigo G-Tape is one example.

• Butyl-based membranes. This type of membrane is very tacky, but doesn’t ooze like bitumen at elevated temperatures. It also adheres better than asphalt membranes and sets faster than acrylic tapes. When applied in cold weather, tack-stapling might be required to hold it in place, but the membrane will self-seal around such penetrations. Trex Seal aluminum-lined flashing tape is the newest generation of butyl-based membranes. Specifically designed for protecting ledgers and compatible with all decking materials, this 11”-wide butyl-based tape combines the best performance features of metal and tape flashing to create a waterproof barrier that provides complete coverage of the ledger board. It also seals any gaps between the ledger and the substructure for optimal protection. Featuring a convenient 5-1/2” double-release liner, Trex Seal is easy to apply for accurate installation and is Code AAMA711 compliant.

Additionally, the aluminum lining reduces or eliminates the need for stapling because it holds its shape better than unlined tapes, and tapes that use a PET lining. Not only does the aluminum lining minimize flex back and slumping, but it allows builders to pre-bend the tape to fit the inside corner formed by the ledger and building wall. In short, Trex Seal remains tacky and flexible, but the aluminum liner makes it more “obedient” than other flashing tapes.

Flashing tapes are proven to preserve a deck’s integrity and longevity. And, with the selection of easy-to-apply options now available, there’s no reason for any deck to be left vulnerable to the elements and premature failure. DS

Dave Kile is the founder and North American sales mgr. for Trex RainEscape, manufactured and sold by IBP, LLC under a Trademark License Agreement with Trex Company, Inc. RainEscape is a federally registered trademark of IBP, LLC (TrexRainEscape.com).

By Sara Graves