Attach Ledger Board to House
Install the 2x10 or 2x12 ledger board with lag bolts, applying flashing tape first. Stagger lag bolts every 16 inches for a secure connection that will support your deck for decades.
Quick Summary
3-4 hours
16 inches O.C.
1/2" lag bolts
Proper flashing
Why Proper Ledger Installation is Critical
The #1 Cause of Deck Collapses
Improper ledger attachment is the leading cause of deck failures and collapses. When a ledger fails, the entire deck can separate from the house in seconds, often during events with many people on the deck. This is not just a structural concern - it's a serious safety issue. Taking time to install the ledger correctly is non-negotiable.
The ledger board is the connection point between your deck and your house. Half of your deck's weight (and everyone standing on it) transfers through this single board into your home's structure. A ledger that's improperly attached, or one that's rotted due to poor flashing, can fail catastrophically.
Water management is just as important as fasteners. Even properly installed lag bolts will fail if water gets behind the ledger and rots the house rim joist. The flashing details described in this guide are essential for long-term durability.
Many building departments now require special inspections for ledger connections, and some jurisdictions require engineered hold-down connectors in addition to lag bolts. Check your local code requirements before starting.
Materials You'll Need
Lumber and Fasteners
- Pressure-treated 2x10 or 2x12 - Length to span entire deck width
- 1/2" x 4" or 5" lag bolts - Hot-dipped galvanized or stainless
- Washers - 1/2" galvanized or stainless washers for each bolt
- Ledger spacers (optional) - Create drainage gap behind ledger
Flashing Materials
- Self-sealing flashing tape - 6" or wider, for behind ledger
- Metal drip cap flashing - Z-flashing or L-flashing for above ledger
- Polyurethane caulk - For sealing penetrations
- Joist tape - Apply to top of ledger where joists rest
Lag Bolt vs. Through-Bolt
Lag bolts are the standard for ledger attachment when you can't access the back of the rim joist. If you can access both sides (from the basement or crawlspace), through-bolts with nuts are even stronger. Check your local code - some jurisdictions require through-bolts or specialized connectors for elevated decks.
Step-by-Step Installation
Calculate Ledger Position
Determine where the top of your ledger should be based on your desired finished deck height. The top of the ledger should be at finished deck height minus the decking thickness (typically 1" for 5/4 decking).
Most codes require the deck surface to be 1-3 inches below the door threshold to prevent water and snow from entering the house. Measure down from the threshold and mark your ledger position accordingly.
Top of ledger = 8" - 2" - 1" = 5" above finished floor level
Remove Siding
Mark the area where siding needs to be removed - this should extend at least 2 inches beyond the ledger on all sides. For the top, extend high enough to install flashing behind the siding above (typically 6-8 inches above the ledger top).
Use a circular saw set to the siding depth to make cuts, being careful not to cut into the sheathing or house wrap beneath. Remove the cut siding carefully - you may be able to reuse pieces at the ends.
Install Flashing Tape
Apply self-sealing flashing tape to the exposed sheathing, starting at the bottom and working up (so upper pieces overlap lower pieces like shingles). The tape should cover the entire area behind where the ledger will sit and extend beyond it.
Press the tape firmly to ensure good adhesion, especially around any existing penetrations like hose bibs or dryer vents. This tape is your primary defense against water infiltration.
Mark and Snap Ledger Line
Using your calculated position, mark the top of the ledger on both ends. Use a long level or water level to ensure these marks are at exactly the same height. Snap a chalk line between the marks.
This line is critical - the ledger must be perfectly level for your deck to drain properly and look right. Double-check the level before proceeding.
Position and Temporarily Secure Ledger
Lift the ledger into position with the top edge aligned with your chalk line. This is a two-person job for long ledgers. Drive a few temporary screws to hold it in place while you drill for lag bolts.
If using ledger spacers (recommended by many builders), install these between the ledger and sheathing now. Spacers create a gap that allows water to drain rather than being trapped behind the ledger.
Mark and Drill Lag Bolt Holes
Mark lag bolt locations in a staggered zigzag pattern - 2 inches from top, then 2 inches from bottom, alternating every 16 inches. The first and last bolts should be within 2 inches of the ledger ends.
Drill pilot holes through the ledger and into the house rim joist. For 1/2" lag bolts, use a 5/16" pilot hole through the ledger and a 1/4" pilot hole into the rim joist. Drill deep enough for full bolt penetration.
Install Lag Bolts
Place a washer on each lag bolt and drive them into the pilot holes using a socket wrench or impact driver with a socket adapter. The bolt should be snug but not over-tightened - you want to compress the wood slightly without crushing it.
Apply polyurethane caulk around each bolt head after installation. This seals the penetration against water. Some builders apply caulk to the bolt threads before installation for even better protection.
Install Drip Cap Flashing
Slide metal Z-flashing or drip cap behind the siding above the ledger. The horizontal leg should extend over the top of the ledger by at least 1 inch. If siding is tight, use a flat pry bar to gently lift it.
The flashing should be continuous across the entire ledger length. If you need multiple pieces, overlap them at least 2 inches with the upper piece on top. Seal joints with caulk.
Lag Bolt Pattern Details
Staggered Zigzag Pattern
The staggered pattern distributes load across more wood grain and reduces the risk of splitting. Here's the standard pattern:
- - First bolt: 2" from end, 2" from top
- - Second bolt: 16" from first, 2" from bottom
- - Third bolt: 16" from second, 2" from top
- - Continue alternating every 16"
- - Add extra bolts at ledger joints (within 2" of each side)
- - End with bolt within 2" of ledger end
Bolt Penetration Requirements
- - Minimum 1.5" into rim joist
- - Through ledger (1.5") + sheathing (0.5-0.75") + rim joist
- - 4" bolts usually sufficient for 2x ledger
- - 5" bolts needed if using spacers
- - Never go through rim joist into house
At Ledger Joints
- - Joints should fall on a floor joist inside
- - Add lag bolts within 2" of joint on each side
- - Leave 1/8" gap between ledger boards for drainage
- - Flash joint with tape before installing second board
- - Seal joint with caulk after installation
Common Mistakes to Avoid
Skipping or Inadequate Flashing
This is the most common and most serious mistake. Without proper flashing, water will get behind the ledger, rot the rim joist, and cause eventual failure. Both tape flashing behind and drip cap above are essential.
Installing Over Siding
Ledgers installed over siding fail for multiple reasons: the siding compresses over time loosening bolts, there's no solid bearing surface, and water gets trapped behind. Always remove siding in the ledger area.
Using Screws Instead of Lag Bolts
Deck screws, even structural screws, don't have the shear strength of lag bolts for ledger attachment. Most codes specifically require lag bolts or through-bolts. Don't substitute.
Attaching to Sheathing Only
The ledger must be bolted through the sheathing into the house rim joist. OSB or plywood sheathing alone cannot support the loads. If you can't locate a rim joist, consult an engineer - you may need a different connection method.
Frequently Asked Questions
What size ledger board should I use for a deck?
The ledger board should match your joist size - typically 2x10 or 2x12 pressure-treated lumber. For most residential decks with joists spanning up to 12 feet, a 2x10 ledger is sufficient. Longer spans or heavy loads may require 2x12. The ledger must be the same depth as your joists since joists will attach directly to it.
How far apart should lag bolts be on a deck ledger?
Lag bolts should be installed every 16 inches on center in a staggered zigzag pattern - alternating between 2 inches from the top and 2 inches from the bottom of the ledger. This pattern distributes the load and prevents splitting. At ledger joints, add extra bolts within 2 inches of each side of the joint.
Do I need to remove siding to install a deck ledger?
Yes, you must remove siding where the ledger attaches. Installing over siding creates gaps that allow water infiltration and prevents solid contact with the house structure. The ledger must bear directly against the sheathing (with flashing between) and ultimately transfer loads to the house rim joist.
What causes deck ledger failures?
Most deck ledger failures result from water damage caused by improper or missing flashing. Water gets behind the ledger, rots the house rim joist, and the fasteners pull out. Other causes include inadequate fasteners (using screws instead of lag bolts), attaching to sheathing only instead of the rim joist, and corrosion from incompatible metals.