Why do most deck collapses start at the ledger board?
Short answer
The ledger is the board that ties an attached deck to the house, and it is the one connection that carries half the deck's weight through a few fasteners into wood you cannot see. When those fasteners are nails instead of bolts, when the flashing is missing so the rim joist behind rots, or when there are no lateral ties, the ledger peels away from the house and the whole deck drops at once. Properly bolted, flashed and tied, it is one of the strongest parts of the deck.
What the ledger does
On an attached deck, the joists run from a beam on posts out in the yard back to the house. At the house they land on the ledger, a board fastened flat against the wall framing. Every joist hangs off it, so roughly half the weight of the deck, the furniture and everyone standing on it goes through the ledger into the house.
That makes it the most heavily loaded connection on the deck, and also the one with the least redundancy. A deck with six posts can lose one and sag. A deck with one ledger that lets go has nothing left to hold the house side up.
Three ways ledgers fail
The first is fasteners. For decades, ledgers were nailed. Nails hold well in shear when they are new, but they pull out as wood shrinks and swells through wet and dry seasons, and they corrode. A nailed ledger can hold for twenty years and then let go during a party, because that is the first time it has carried a full crowd. Current residential code calls for through-bolts or approved structural screws at a specified spacing, and the deck provisions in the International Residential Code, which California adopts as the California Residential Code, include tables for that.
The second is rot behind the ledger. Water running down the wall gets trapped between the ledger and the house. Without flashing that directs it out over the face of the ledger, it soaks the rim joist and sheathing behind. The ledger itself can look fine while the wood the bolts are threaded into has turned to mulch. Then the bolts simply pull through.
The third is lateral load. People moving on a deck push and pull it away from the house. Fasteners through a ledger are good at carrying weight downward and poor at resisting that outward pull. Newer code provisions add hold-down tension devices, often called lateral load connectors, that tie the deck joists back into the house floor framing.
Why coastal North County makes it worse
Marine air carries salt, and salt accelerates corrosion of ordinary galvanized nails and bolts. Morning fog wets exterior wood most days of the year even when it has not rained. Behind a ledger, that moisture has nowhere to go. Levi routinely finds the stucco or siding below a ledger streaked and the sheathing behind it soft on decks that otherwise look well kept. Hot-dip galvanized or stainless hardware and real flashing are not upgrades here. They are the baseline.
How to tell if your ledger is a risk
From below, look at how the ledger is fastened. Nail heads only, with no bolt heads or structural screw heads visible, is a red flag. Look for a gap between the ledger and the wall, or a ledger bowed outward between fasteners. Look for staining on the wall below. Probe the ledger's lower edge and, where you can reach it, the rim joist behind.
Look for flashing. There should be a metal or membrane flashing that comes down the wall, over the top of the ledger, and out past its face. If the ledger top is bare wood against stucco or siding, water has been getting in behind it since the day it was built.
Check whether the deck is tied back laterally. Hardware that connects a joist through the rim into the house floor framing is visible from below as a bracket and bolt near the house.
- Nails only, no bolts or structural screws
- Any gap or bow between ledger and wall
- No visible flashing over the ledger
- Staining or soft stucco below the ledger
- No lateral tie hardware near the house
What a proper ledger repair involves
The decking comes up along the house and the ledger comes off. That is the only way to see the rim joist and sheathing behind it. Rotted framing is cut back and replaced, then the wall is re-weatherproofed, the new ledger is bolted to sound framing at code spacing, flashing is installed over it, and lateral connectors are added. On the balcony project in Levi's portfolio, this was exactly the sequence, and it was the connection to the house that had been doing the most damage.
Some ledger conditions call for a structural engineer, especially on second-story balconies, where the wall framing itself is damaged, or where the deck was never designed to attach. Levi will say so when that is the case rather than guess.
Related questions
Is a freestanding deck safer than an attached one?
It removes the ledger as a failure point, which is why some builders prefer it. It needs its own beam and posts along the house side and must be stiff enough to resist sway on its own. Either approach is safe when built correctly.
My deck is nailed to the house but has never had a problem. Should I worry?
A nailed ledger has no reserve for the day the deck carries a crowd, and the nails are likely corroding. Having it retrofitted with bolts, flashing and lateral ties is a modest project compared with what a failure costs, and it does not require rebuilding the deck.
Does Carlsbad require a permit to replace a ledger?
Structural repairs to a deck generally fall under permit requirements. Check with the Carlsbad Building Division before the work begins. A permit also puts an inspector's eyes on the most important connection in the deck.
Sources and further reading
- International Residential Code (ICC) (codes.iccsafe.org)
- City of Carlsbad Building Division (www.carlsbadca.gov)