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Deck Flashing

The Connection between the House and Deck Must be Protected from Water Intrusion with Deck Flashing

By Mark J. Donovan

Deck flashing installation is an extremely important part of deck construction. As a matter of fact, the leading cause of catastrophic deck collapses is the failure in the connection between the deck ledger and the house. Failure between the deck ledger and house connection is typically caused by either the lack of deck flashing or the improper installation of it.

Deck flashing plays a major role in protecting your deck and home from water damage. Deck flashing’s main purpose is to prevent water intrusion behind the deck ledger board and eventually into the home.


Water that can get behind the deck ledger board can lead to sill and band joist dry rot as well as connector corrosion. In addition, mold and mildew growth can also occur. All of these issues can eventually cause the deck to pull away from the home leading to catastrophic deck failure. Unfortunately, the catastrophic deck failure often occurs when extra weight is placed on the deck, such as when the deck is holding several people. As a result, it is critical to prevent water intrusion behind the deck ledger by properly installing deck flashing.


Equally important to installing deck flashing when constructing a deck is to install the right type of flashing. Deck flashing is available in galvanized, copper, aluminum and stainless steel, as well as PVC. Deck flashing is most commonly sold in roll form that can be shaped, or in Z or L pre-shaped sections. A waterproof membrane is also frequently used in conjunction with the deck flashing to provide extra protection against water leaks and to isolate certain deck flashing types from ACQ (Alkaline Copper Quaternary) treated lumber.


When fastening metal deck flashing to house siding and ledger boards, use fasteners of the same type of metal. Using fasteners that are of dissimilar metals can lead to chemical reactions and corrosion between the metal deck flashing and fasteners. The chemical reaction between the two dissimilar metals can eventually lead to catastrophic deck failure. In addition, aluminum or electro-galvanized deck flashing should not be used with ACQ treated lumber as it contains copper. Again, the chemical reaction between the dissimilar metals can cause deck failure.


Perimeter deck flashing should be installed where the deck attaches to the house.

G185 galvanized flashing, stainless steel or PVC flashing should be used when the deck flashing is to be in contact with ACQ treated lumber.

Photos by Mark Donovan

This said, hot dipped galvanized (G185) perimeter and ledger deck flashing is specifically designed to be used with ACQ treated lumber. The company Everflashing sells this type of specialty deck flashing product as well as many other types of unique perimeter flashing products.

PVC, Stainless steel, and Copper deck flashing can also be used with ACQ treated lumber. Stainless steel flashing is also the perfect type of deck flashing for salt water environments. Aluminum deck flashing can often be found in various colors and is limited for use with L3 and Micropro lumber applications, or with a membrane barrier. Again, Everflashing offers a unique Aluminum deck flashing product that is available in a variety of colors.

It is also important to use the proper width deck flashing. Deck flashing should tuck up at least 2 to 3 inches behind the house siding to ensure the prevention of water intrusion.

So if you have plans to build a deck, make sure to include deck flashing, use the right type, and install it per the manufacturer’s recommendations.

For help on building a new Deck, see HomeAdditionPlus.com's Deck Installation Bid Sheet. The Deck Installation Bid Sheet will teach your how to hire the right deck contractor, and help to ensure that your deck project is completed on time and budget.

How to Finance your Deck Project -  can help provide funds for your new home improvement project if financing is required.

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