Do you need flashing behind ledger board?

Whether or not you need flashing behind ledger board is a common question that comes up during home exterior projects. Ledger boards provide structural support for elements like decks, and proper moisture management is crucial to prevent rot and other damage. There are a few key factors to consider when deciding if flashing is needed behind your ledger board.

What is a ledger board?

A ledger board is a horizontal board that is bolted to the exterior wall of a home. It provides a sturdy surface to attach and support horizontal elements like a deck. Ledger boards transfer the weight and load of the deck to the home’s band joist and wall framing. They are typically made of pressure treated lumber for durability.

Purpose of flashing behind a ledger board

Flashing serves an important purpose behind a ledger board. It creates a moisture barrier between the ledger board and the home’s exterior wall. This prevents rain and water from getting behind the ledger and causing damage over time. Here are some key reasons flashing is important:

• Prevents rot: Trapped moisture can lead to rotting of the ledger board, band joist, and wall framing.
• Stops insect damage: Excess moisture attracts wood boring insects like termites and carpenter ants.
• Improves durability: Flashing protects structural connections and extends the lifespan of the deck.
• Avoids leaks: Stops water from penetrating behind the siding into the wall framing.

ledger board flashing code requirements

Most building codes and standards require flashing to be installed behind ledger boards attached to homes and structures. Here are some of the specific code requirements:

• International Residential Code (IRC): Section R507.2.2 requires flashing and a way to drain water to the exterior of the building.
• International Building Code (IBC): Section 1604.8.3 requires corrosion-resistant flashing with a drip edge be installed above ledger boards.
• AWC DCA 6: The American Wood Council standard requires flashing that extends up the wall at least 2″ above the ledger board.
• CertainTeed: Recommends self-adhered membrane or similar flashing behind the ledger per building codes.

It’s crucial to consult your local building codes for the exact specifications and flashing materials permitted in your area. Most jurisdictions require rigid, durable flashing like galvanized metal or adhesive membrane.

Are there any exceptions where flashing is not needed?

There are a few exceptions where building codes may not require flashing behind a ledger board:

• Interior ledger boards not exposed to weather.
• Cases where the existing house siding or exterior finish is removed prior to installing the ledger.
• If there is a moisture barrier in the wall framing behind the ledger location.
• On solid concrete or masonry exterior walls.

However, it is still a smart best practice to install flashing even in these situations when possible. The only time flashing would clearly not be needed is if the ledger board is completely interior and not exposed to the outdoors at all.

How to install flashing behind a ledger board

Here are some general guidelines on how to properly install flashing behind a ledger board:

1. Cut the ledger board to length and temporarily secure it in place on the wall. Make sure it is level.
2. Cut the flashing to overlap the wall siding by at least 2 inches above and below the ledger area.
3. Create a slit in the siding just above the ledger and slip the flashing underneath up to the 2″ point.
4. Apply primer then adhere the back of the flashing fully against the wall sheathing.
5. Secure the top of the flashing with house wrap tape for waterproofing.
6. Install the ledger board permanently with lag screws into the wall framing.
7. Seal the top edge of the flashing with caulk for added water protection.

Be sure to follow manufacturer instructions for proper flashing installation. Also consult your local building codes for any additional requirements in your area.

Flashing materials for ledger boards

There are several suitable flashing material options when installing behind a ledger board:

• Self-adhered flashing membrane – Composite material applied with primer, easy to form around ledger and siding.
• Aluminum flashing – Shapes easily around ledger, durable and corrosion resistant.
• Copper or galvanized steel – Long lasting metals that resist damage.
• Rubberized asphalt – Flexible, can seal around fasteners and irregular surfaces.
• EPDM – Rubber sheets that are weatherproof and handle expansion.

Always use flashing rated for exterior exposure and approved for use as code compliant ledger board flashing. Your climate and budget will help determine the ideal product.

Tips for proper ledger board flashing

Here are some additional tips for making sure your ledger board flashing is installed correctly:

• Extend the flashing 2 inches minimum beyond the ledger in both directions
• Make sure there are no gaps where moisture could penetrate
• Caulk the top edge and seams for extra leakage protection
• Use flashing compatible with your siding type
• Consider using an adhesive membrane for easier installation
• Place house wrap over the flashing for added water resistance
• Divert rainwater runoff from the ledger area if possible

Signs you need new ledger board flashing

Here are some signs that moisture is getting behind your existing ledger board and that you need new flashing installed:

• Visible water damage on siding near the ledger board
• Dark streaking on the ledger board
• Soft, decaying wood anywhere near the ledger
• Swollen, cracked, or warped ledger board
• Rust on lag screws, bolts, or metal parts
• Peeling paint near the ledger board
• Evidence of pests like termites or carpenter ants

Even a small gap or lack of adhesion in the existing flashing can allow moisture ingress. If you notice any of these warning signs, it’s best to have new flashing installed.

Conclusion

Proper moisture management is key to a long lasting deck. Flashing behind the ledger board provides important protection from water damage and deterioration. Building codes require it in most exterior ledger board applications. Make sure to install code compliant flashing, inspect regularly, and replace any compromised areas to protect your investment and prevent costly repairs down the road.