When Does a Deck Ledger Board Need Repair?

The ledger's job on an attached deck

The ledger is the board fastened to the side of the house that carries the house end of every joist on an attached deck. Roughly half the weight of the deck, the snow on it and the people standing on it goes through that one connection into the home's rim joist. If the ledger pulls away, there's nothing else holding that side of the deck up.

That's why the ledger gets more attention in the code than any other single part of a deck, and why it's the first thing to check on an older one. It's also a part older decks often got wrong: a ledger nailed to the house, with no flashing above it, was a common way to build before the current code details.

What are the signs of ledger failure?

Most ledger problems show up as a pattern of small signs rather than one obvious failure. Look from the yard, from under the deck, and from inside the house where the deck attaches.

From under the deck

• Rows of nail heads and no bolt heads or washers. A ledger held only by nails is not a code-compliant attachment.
• A gap opening between the ledger and the house, or a ledger that's rotated so its top edge leans out.
• Rust streaks running down from fasteners, or bolt heads that have lost much of their section to corrosion.
• Dark, soft or crumbling wood on the ledger or on the house rim joist behind it. Push an awl in; sound wood resists.
• No metal flashing visible above the ledger, or caulk smeared along the top edge in place of flashing.
• Joist hangers pulling away from the ledger face, or hanger nails backing out.
• The ledger fastened to stone or brick veneer instead of to the house framing.

From the deck surface

• The deck slopes away from the house more than it used to, or the first board has dropped below the door threshold.
• Extra bounce close to the house compared with the middle of the deck.
• Water pooling at the door because the deck has settled toward the wall.

From inside the house

• Water stains, mold or soft wood on the basement or crawlspace rim joist where the deck attaches.
• Swollen or stained flooring, trim or drywall just inside the door to the deck.
• Fastener tips or bolt ends visible inside with rust around them.

Any one of the structural signs, such as nails only, a gap, or rot behind the ledger, is reason to stop using the deck for gatherings until it's assessed. Our repair or replace checklist covers the rest of the frame.

Why ledger flashing fails so often

Because water has a direct path to the house at that joint, and it only takes one gap. Rain, snowmelt and sprinkler spray run across the deck boards toward the wall, drop through the board gaps, and land on the top of the ledger. Without flashing, that water sits between the ledger and the house, soaks the rim joist, and starts decay you can't see from outside.

The 2018 IRC as adopted in Idaho addresses this directly. Section R507.2.4 requires flashing to be corrosion-resistant metal at least 0.019 inch thick, or an approved nonmetallic material compatible with both the structure and the decking. The footnote to the ledger fastener table adds that ledgers shall be flashed in accordance with Section R703.4 to prevent water from contacting the house band joist. Caulk is not flashing. A bead of sealant along the top of a ledger has to survive sun, heat and constant movement, and it doesn't hold up for long.

Boise's climate is hard on a weak flashing detail. NOAA's 1991–2020 normals record 108 nights a year at or below 32°F, with only 16 days that stay frozen all day. Snow that piles against the house wall melts by day and refreezes at night, and water that gets behind a ledger goes through that cycle over and over. The deck outside a back-door slider is a typical spot: foot traffic, snowmelt and a door threshold all meet at the ledger.

What does the IRC require for ledger fasteners?

Idaho's residential code is the 2018 IRC with state amendments, and Boise, Meridian, Nampa and Eagle review deck plans to it. Section R507 sets the ledger rules. Here is what an inspector or a builder assessing your ledger is checking against:

The fastener table covers half-inch lag screws and half-inch bolts, with spacing set by the joist span. Through-bolts need access from inside the rim joist and a nut on the back; lag screws need a solid, full-depth band joist to bite into. Which one fits depends on what's behind the wall, which is a judgment made on site, often with the interior ceiling or rim insulation opened up. Boise sits inside the table's snow basis: the city's ground snow load is 20 psf, under the table's 40 psf snow limit, and a table note says snow isn't assumed to act at the same time as the 40 psf live load.

The American Wood Council's DCA 6 guide, which follows the IRC's prescriptive deck rules, illustrates the same details with drawings and is a useful reference if you want to see what a compliant ledger looks like before talking to a builder.

Lateral load connections and when a deck needs them

The ledger bolts resist the deck pushing down. The lateral connection resists the deck pulling away from the house horizontally, the motion that turns a crowded deck into a collapse when the ledger lets go. Section R507.8 requires an attached deck to be designed for lateral loads, and R507.9.2 says those loads have to be transferred to the ground or to a structure capable of carrying them there.

R507.9.2 gives two prescriptive ways to meet that. One uses hold-down tension devices in at least two locations per deck, each within 24 inches of an end of the deck and each rated at not less than 1,500 pounds allowable stress design capacity. The other uses at least four devices rated at not less than 750 pounds each. Both tie the deck joists through the ledger and band joist into the house floor framing.

Many decks built before these details became standard have no lateral hardware at all. On an older deck with a sound, bolted, flashed ledger, adding lateral hold-downs can be a contained repair. On a deck where the ledger itself is failing, they're part of a full reattachment.

Can the ledger be repaired, or should the deck be freestanding?

It depends on what's behind the ledger. There are three common outcomes:

1. Reattach on sound framing. If the house rim joist is dry and solid and the house wall is framed, not veneered, the ledger can be replaced or refastened with code-compliant bolts or lags, new flashing integrated with the house wrap, and lateral hold-downs.
2. Repair the house first. If water has already rotted the rim joist or floor framing behind the ledger, that wood has to be repaired before anything bolts to it. That is house structure, and depending on the extent it can call for an engineer.
3. Make the deck self-supporting. If the wall is stone or brick veneer, or a positive connection can't be verified, R507.8 and R507.9.1.1 point to a freestanding deck: a new beam on posts near the house, on footings that reach at least 24 inches deep in Boise, with no reliance on the ledger. Our footing depth guide covers that sizing.

Sometimes the right answer is none of these. If the ledger, joists and footings are all at the end of their life, a full deck replacement is cheaper than rebuilding the connection on a frame that's failing everywhere else.

Why is ledger repair permitted structural work in Boise?

Because the ledger is the primary structural connection on an attached deck, and the city reviews it as one. Boise requires a permit for any deck more than 12 inches above grade, a stricter trigger than the 30 inches in the model code's deck exemption. Boise's #402 submittal checklist asks for the deck's construction details and its ledger connection detail, and the #406 checklist for additions and alterations asks for a framing plan, elevations and a footing-to-rail section, with stamped engineering for decks more than 6 feet above grade.

Replacing or reattaching a ledger on a deck more than 12 inches up changes the structure the city permits and inspects, so plan on a permit and an inspection. Boise's building division can confirm the exact scope for your deck at 208-608-7070; our Boise permit guide has the details. Elsewhere in the valley, Meridian's handout lists any deck attached to the house among the decks that need a permit, Nampa requires a permit for decks more than 12 inches high, and Eagle's residential checklist asks for ledger details. See the Meridian deck permit page for that city's trigger.

The permit protects you as much as the city. An inspection record showing a code-compliant ledger connection is the document a future buyer's inspector will ask about, and an unpermitted structural repair can come up at sale.

Why shouldn't you treat ledger repair as a weekend project?

This page deliberately doesn't give step-by-step repair instructions, for three reasons. First, the deck has to be temporarily supported while the ledger is off, and a mistake there drops the deck. Second, the job opens the house's weather barrier at the rim joist, and getting the flashing and house wrap lapped correctly is what keeps the next ledger from rotting. Third, the condition of the framing behind the ledger is unknown until it's opened, and what you find decides which of the three outcomes above applies.

If you're doing work on your own primary residence, Boise does allow homeowners to pull their own permit, and the inspection is your check. For most people, though, ledger work is the place to hire. Our guide to hiring a deck builder covers registration, insurance and how to write the scope.

How a ledger inspection works

A useful ledger assessment starts under the deck and inside the house. It covers what the ledger is fastened to, the fastener type, size and pattern against Table R507.9.1.3(1), the flashing detail, the condition of the rim joist behind it, the joist hangers, and whether any lateral hardware exists. Ask whoever does it to tie each finding to the IRC section it relates to and to sort the list into safety items, durability items and cosmetic ones, so you can decide what to fix with the facts in front of you.

Ledger repair cost depends on what's found behind the ledger and whether the house framing needs work; the deck repair cost guide has sourced ranges for common repairs. To have a ledger looked at, start with our deck repair service in Boise or request an estimate.