How To Attach a Deck to a House

The joint between your deck and your house is a crucial feature to get right. Failing to properly secure the deck can lead to water intrusion into your home—or even collapse. This video and guide will walk you through attaching a deck to your house, highlighting the proper techniques and safety measures with This Old House general contractor Tom Silva.

Pro Tip: Tom Silva, general contractor on This Old House, warns against running lag bolts in a straight line when attaching a ledger board: “I don’t want to run a straight line with the lag bolts because I could actually split this with the weight of the joist.” Staggering your fasteners protects the structural integrity of both the ledger and the rim joist.

Preparing for Deck Attachment

Before attaching the deck, thoroughly inspect the area where it will connect to the house. Check for any signs of rot or damage in the existing structure. An inspection can also reveal hidden issues, such as structural weaknesses or water damage, that might jeopardize your deck’s stability. Addressing these issues beforehand helps your deck remain secure.

Pro Tip: This Old House contractor Tom Silva pays particular attention to the beam that connects the deck to the house. “It’s where 99 percent of mistakes are made,” he says. To prevent moisture from getting trapped between the deck and the house—which can encourage rot—Tom creates a gap for air using spacers cut from scraps of pressure-treated wood.

Confirm the house’s framing can support the additional load of the deck. If you’re unsure, a structural engineer should be able to help.

Finally, identify the location of the house’s sill plate, as this is where you’ll attach the ledger board.

How you connect the ledger to the house depends on the house’s framing. According to This Old House Magazine, older houses often have a thick timber mudsill rather than a rim joist, which requires driving lag screws in a zigzag pattern every 2 feet. Houses of more recent vintage generally have a thinner 2x rim joist resting on top of a 2x sill plate, which calls for lag screws into the sill plate and through bolts into the rim joist. For attaching a ledger directly to the foundation, masonry expansion bolts are the preferred option.

Tools You’ll Need

You’ll only need a few basic carpentry tools for this job.

Installing Proper Flashing for a Deck

Waterproof flashing is vitally important for preventing moisture damage. This is typically metal sheeting that will sit between the deck and house. Here’s how to install it:

1. Remove any existing siding in the attachment area.
2. Apply a layer of flexible adhesive-backed flashing over the sheathing.
3. Install a second layer of flashing as counterflashing for added protection.

Use galvanized flashing rather than aluminum. Copper-laden runoff from pressure-treated wood will corrode aluminum over time. Also, be careful not to penetrate the flashing with long nails when attaching metal joist hangers—either attach the hangers and hammer over the nail tips before bolting the ledger to the house, or switch to short, thick hanger nails and reduce the load on each hanger as directed by the manufacturer.

If You’re Installing a New Deck

If your new deck will be replacing a set of outdoor stairs, remove the old flashing from behind the ledger board and inspect plywood sheathing for rot. If necessary, patch the sheathing before continuing. Then:

1. Fasten metal L-brackets to the end of the rim joists with hanger screws. Set the ends of the rim joists against the house and screw the L-brackets into the sheathing. If necessary, create spacers by attaching pieces of decking to the top side of the frame that goes against the house.
2. Install the ledger between the rim joists and fasten it to the house with 3-inch decking screws.
3. Use an impact wrench to drive 1/2-inch-diameter galvanized lag screws with washers through the ledger and into the sill of the house.

If You’re Reattaching an Existing Deck

Reattaching an existing deck can be a little more involved. You’ll want to make sure everything is restored to proper alignment.

1. Temporarily brace the deck against the house with 2-by-4-foot stakes and 2-by-6-foot diagonal braces. If necessary, raise the deck to its original height by temporarily installing 2-by-6-foot support posts beneath the deck. Tap the posts into place with a sledgehammer.
2. Drill a 1/2-inch-diameter screw-shank clearance hole through the ledger board but not into the sill plate. Position the hole 3 inches below the upper edge of the ledger and at a slightly upward angle.
3. Place a 1/2-inch by 10-inch galvanized lag screw with a washer into the hole, then use an impact wrench to drive the screw into the sill plate. Repeat to install one lag screw in each joist bay.
4. If there’s a gap between the ledger and the house foundation, use filler pieces of pressure-treated wood to fit snugly into the space. The filler pieces will prevent the ledger from splitting when it’s bolted into the foundation.
5. Use a hammer drill fitted with a 1/2-inch-diameter masonry bit to bore holes through the ledger, in through the filler pieces, and into the foundation; then use a hammer to tap 1/2-inch by 10-inch masonry wedge anchors into the holes.
6. Tighten the hex nut on the wedge anchor with the impact wrench. Continue to install masonry anchors, spacing them 36 to 48 inches apart.
7. If the existing joist hangers are undersized or corroded, reinforce each one with an engineered lumber joist hanger. Slip the engineered lumber joist hanger over the existing hanger and secure it with galvanized hanger nails.

Addressing Common Attachment Issues

Identifying and resolving attachment issues early can save you from costly repairs down the line.

Gaps Between Ledger and Foundation

If you encounter a gap between the ledger board and the house foundation, cut pressure-treated wood filler pieces to fit snugly in the space. Install the filler pieces before securing the ledger to prevent splitting. Use longer masonry anchors to accommodate the additional thickness.

Filling these gaps appropriately helps the ledger board stay securely fastened, creating a stable connection between your home and the deck.

Undersized or Corroded Joist Hangers

Inspect all existing hangers for signs of corrosion or improper sizing. Replace any damaged or undersized hangers with new, appropriately sized ones. Consider using engineered lumber joist hangers for added strength and durability.

Inadequate or damaged hangers can compromise the entire structure, so addressing these issues promptly is recommended.

Tom Silva, This Old House general contractor, explains that in 2003 the chemical makeup of pressure-treated wood changed to remove arsenic, and the new formulation can cause a galvanic reaction with certain metals. “You want to make sure that the fastener is rated for the material,” Tom advises. Always use fasteners and hangers rated for use with modern pressure-treated lumber—typically hot-dipped galvanized or stainless steel—to prevent premature corrosion that can lead to connection failure.

Long-Term Deck Stability

To maintain your deck’s stability over time:

• Conduct regular inspections of the attachment points and fasteners.
• Check for signs of water damage or rot, especially around the ledger board.
• Tighten any loose bolts or screws as needed.
• Reapply waterproof sealant to exposed wood surfaces every few years.

Routine maintenance is imperative for the long-term stability and safety of your deck. 

Our Conclusion

Attaching a deck to your house requires careful planning and execution. Using proper materials, following correct installation techniques, and regularly maintaining the structure can create a secure and enjoyable outdoor living space that will last.

Conduct regular inspections of the attachment points and fasteners, and check for signs of water damage or rot, especially around the ledger board. Tighten any loose bolts or screws as needed, and reapply waterproof sealant to exposed wood surfaces every few years.