When building a deck onto your home it is imperative that deck flashing be installed on the deck ledger boards. Without deck flashing, your deck, home and personal wellbeing are at risk. Deck flashing prevents deck water run-off from seeping behind the deck ledger board and behind the home siding. If water were to seep in behind the home siding, rot, insect, and mold and mildew problems will quickly arise. Decks have also been known to detach and fall off homes when deck flashing has not been installed or installed improperly over the deck ledger boards.

What is Deck Flashing?

Deck flashing is a thin strip of metal, which slides up under the first row of clapboard siding that sits just above the surface of the finished deck, and wraps over and partially down the side of the deck’s ledger board.

Until January 1, 2004 you could use aluminum or galvanized flashing with pressure treated decks. Up until January 2004, pressure treated wood used a preservative known as chromated copper arsenate (CCA) for protecting the wood. This product is now banned.

New pressure treated lumber uses alkaline copper quat (ACQ) as a preservative, which is less harmful to the environment and to you. The problem with this new pressure treated lumber, however, is that the ACQ product contains much higher levels of copper. Copper is not a safety issue by itself, however it is more corrosive when put in contact with steel and other metals. In time this corrosive action could lead to deck flashing failure if aluminum or galvanized flashing were used with this newly treated lumber.

Make sure when installing the decking that you do not punch nails or screws into the deck flashing as this will enable water to seep through the nail holes into the deck flashing and behind the deck ledger board.

At deck flashing junctions, overlap the sections of deck flashing by 6-10 inches and apply a bead of silicone caulk.