Whether to repair or replace a rotted or leaking deck in Seattle depends on where the rot is, not on how the boards look. Rot in a few boards, one railing post or one set of stairs calls for rotted deck repair, from $199. Rot in the joists, the posts or the ledger board that ties the deck to your house is a different job, and that is where many repairs turn into a deck rebuild.
Below: how to check your deck, what each sign means, how damaged deck repair compares with replacement on price, what leaking deck repair involves over a room or garage, when Seattle asks for a permit and how to keep rot away. The inspection is free with your on-site estimate.
Start With a 15-Minute Self-Check
You need a flashlight, a screwdriver and a phone camera. Backyard deck repair often starts with one soft board, so look past it to the frame underneath.
- Probe the wood. Push the screwdriver into boards, joists, posts and the ledger. If the tip sinks 1/4 to 1/2 inch with little effort, a sliver lifts out without splintering or the wood feels spongy, decay may be present.
- Look underneath. Shine the light on joist tops, the ledger, post bases and beam-to-post joints. Brown or bleached patches, wood that stays wet and wood cracked across the grain into small cubes are signs of rot.
- Check the ledger. Its bolts or screws should be tight and rust-free. Nails alone, or a gap opening between the ledger and the house, need attention.
- Walk the deck. It should look even and should not sag, sway or bounce.
- Shake the railing and stairs. Posts, rails and stair stringers should feel solid.
- Look for water. Stains on the wall or ceiling below, or wet siding at the ledger, point to a leak.
Gray boards, mildew and light moss on wood that is still hard are usually surface wear, not rot. Photograph anything soft, stained or loose before the visit. The North American Deck and Railing Association’s homeowner checklist covers the same points, and a professional deck inspection checks what you cannot reach.
Where Seattle Decks Rot First
Rot is a fungus, and it needs water. Forest Service research shows serious decay only happens when wood is wetted by rain or condensation or sits on wet ground; humid air alone is not enough. Seattle’s wet season keeps decks damp from fall into spring. Rot shows up first where water sits:
- The tops of joists, where water gets in through fastener holes under the boards and works down.
- Board ends and the joints where two boards meet over a joist.
- Post bases, especially posts set in concrete or wet soil, where water collects against the wood.
- The ledger, and the house wall behind it, when the flashing is missing or too short.
- Spots under downspouts and sprinklers, and shaded corners that never dry.
Repair or Replace a Rotted Deck: What Each Sign Means
In a deck repair or replace decision, each sign points to one of four outcomes: restore, repair one part, resurface on the kept frame, or rebuild.
| What you find | Usually | Starting price |
|---|---|---|
| Gray boards, mildew or moss on hard wood | Restore | Cleaning from $100; restoration from $600 |
| One or two soft, split or cracked boards | Repair | From $125 per board |
| Loose railing post or wobbly rail | Repair | Repairs from $199; new railing from $20 per linear ft |
| Loose or soft stair treads | Repair | From $25 per step |
| Many worn boards on a solid frame | Repair: resurface on the kept frame | From $125 per board |
| Rot in one joist or one post base | Repair | Repairs from $199 |
| Water stains on the wall or ceiling below | Repair the flashing or membrane | Priced after the free inspection |
| Rot in several joists, beams or posts; sag or bounce | Replace | Wood from $18 per sq ft; composite from $28 |
| Soft or loose ledger with rot that reached the joists | Replace | Wood from $18 per sq ft; tear-out from $3 |
| Same spots failing every year on an older deck | Replace | Wood from $18 per sq ft |
Worn finish on sound wood is a deck restoration job. Once rot reaches the frame, the on-site frame check decides between a repair and a rebuild.
Rotted Boards vs Rotted Framing: When a Repair Becomes a Deck Rebuild
Rotted boards are the easy case. A soft or split board comes out, a matching one goes in, and the joist under it gets checked. If the joists, beams, posts and ledger are solid, you keep the frame and pay only for what failed, the work our deck repair service handles.
Rotted framing is different, because rot weakens wood before you can see it. Forest Products Laboratory tests found decay can cut wood strength by more than half while it is still invisible. Framing that already shows visible decay, soft, crumbling or cracked into cubes, has lost much of its strength.
- One rotted joist is often sistered: a new treated joist is bolted alongside the old one.
- A soft post base is replaced, not patched: the deck is shored up and a new post goes on a metal base that keeps it off the concrete.
That is why new boards on a decayed frame fail again. Deck rebuilds that keep a sound frame and replace only the boards and railing save on framing labor, which Angi lists at $11 to $15 per square foot in Seattle. When the frame is done, a full deck replacement resets the clock. A deck that sags, bounces or pulls away for reasons other than rot is covered in our structural deck repair guide.
A Rotted or Loose Ledger Board
The ledger is the board bolted to your house that carries one side of the deck, and the North American Deck and Railing Association calls it a common source of deck failure. Water gets behind it when the flashing is missing, too short or laid over the house wrap instead of tucked behind it, and the rot can spread into the wall sheathing and the house rim joist.
Seattle’s code requires an attached deck to be positively anchored to the house, never with nails alone, using hot-dipped galvanized or stainless fasteners, with flashing where the deck meets the wall. The SDCI deck guidance adds that the ledger must not pull away in an earthquake. A ledger cannot hang on brick, stone or masonry veneer; those decks stand on their own posts.
The repair opens the boards next to the house and the siding at the ledger, replaces rotted sheathing or rim joist, installs a new ledger or new fasteners and flashes it up the wall behind the house wrap. If the rot reached the joists, replacing the deck is usually the better spend.
Stay off the deck if the ledger is pulling away, the deck sways, a post is soft at the base or a railing moves when you lean on it. Have it checked before anyone uses it again.
Leaking Deck Repair and Waterproof Decks Over a Room or Garage
Leaking deck repair starts with finding where the water gets in. On a standard deck the usual culprit is the ledger flashing, and the leak shows as stains on the wall, in the basement or on the ceiling below. The fix is the ledger repair above.
A deck over a living space or a garage has a waterproof membrane, either as the walking surface or under it, laid on plywood sloped at least 1/4 inch per foot and turned up the wall behind the building paper, usually 4 to 8 inches depending on the product and local code. Door thresholds, edges and anything that passes through the membrane, such as posts, are the weak points where leaks usually start. Our rooftop deck page shows how these decks are built.
Waterproof deck repair cost depends on how far the water got. The work opens the leak area, replaces wet sheathing or framing and re-seals the membrane, flashing and threshold, so it is priced after the free inspection. Our deck leak repair page shows what that inspection covers.
Rotted Deck Repair Cost vs Replacement Cost in Seattle
A single deck repair in Seattle starts at $199, and a rotted board is replaced from $125 per board. In Angi’s Seattle figures the average deck repair comes to $3,248, most jobs land between $1,276 and $5,231, and the low and high ends sit near $400 and $12,000. The Seattle deck cost guide breaks down the rest of the price lines.
The cost of a structural rot repair follows the damage, not the board count. Sistering a joist or swapping a post base is a contained job; a ledger, the sheathing behind it and several joists cost more.
To decide, set the repair quote next to the price of a new deck. A 12×16 deck covers 192 square feet: rebuilt in wood, from $18 per square foot plus tear-out from $3, it starts at about $4,030, and in composite, from $28, at about $5,950. When a repair quote gets close to that figure, a rebuild is usually the better spend, and the written estimate can show both prices.
You get up to 25% off qualifying projects, and your exact price comes in writing after the free on-site estimate.
Permits for Deck Repair and Replacement in Seattle
For a repair-or-replace decision the permit question splits in two: repairs follow Seattle’s minor-repair exemption, and a rebuild follows the same rules as a new deck.
For repairs, the city’s permit guidance says minor repairs or alterations that cost $6,000 or less in any six-month period need no permit, but any work on load-bearing supports needs one no matter how small, and the usual exemptions do not apply in an environmentally critical area.
- Swapping boards, railing parts or stair treads: usually no permit.
- Replacing rotted joists, beams, posts or a ledger: this is work on load-bearing supports, so plan on a permit.
- Tearing out and rebuilding the deck: a permit applies as for a new deck, which Seattle requires above 18 inches, on a roof or in an environmentally critical area; SDCI’s deck page lists the full thresholds.
Heights, setbacks and the permit steps are in our Seattle deck permit guide. The written estimate states who handles the permit.
How to Keep Rot From Coming Back
A repair lasts when the water source is fixed with it:
- Keep the gaps between boards open, and clear leaves and needles from them and from where the deck meets the house.
- Flash the ledger with corrosion-resistant flashing that laps over it and runs up the wall behind the house wrap.
- Tape joist and beam tops before new boards go down, so fastener holes do not funnel water in.
- Use ground-contact treated lumber for posts, joists and beams, and brush wood preservative onto every field cut, which Seattle’s code requires for treated wood.
- Set posts on metal bases above concrete footings that sit at least 12 inches below undisturbed ground.
- Recoat wood every one to three years, depending on sun and wear, and check the finish every fall.
Professional deck staining starts at $1 per square foot, a small cost next to a frame repair after another wet winter.
Rotted Deck Repair or Replace: Common Questions
Can a rotted deck be repaired, or does it have to be replaced?
Yes, a rotted deck can be repaired when the rot stays in the boards, one railing, the stairs, one joist or one post base and the rest of the frame is solid. When rot has spread into several joists or a beam, ledger rot has reached the joists, or the deck sags or sways, a rebuild usually beats patching the same frame again.
How much does it cost to repair a rotted deck in Seattle?
Rotted deck repair in Seattle starts at $199 for a single fix, and a rotted board is replaced from $125 per board. Rot that stays in the boards, a stair or one joist is a contained repair. Rot in the joists, posts or ledger is structural work priced after the free inspection, and Angi’s Seattle figures put the average deck repair at $3,248.
Is it safe to use a deck with rot?
A deck with rot is not safe to use when the rot is structural: the ledger is pulling away from the house, the deck sways or bounces, a post is soft at the base or a railing moves when you lean on it. Keep everyone off it until the frame is checked. A free deck inspection tells you which parts are safe and which need work first.
Do I need a permit to repair my deck in Seattle?
Most surface deck repairs in Seattle need no permit: the city exempts minor repairs or alterations that cost $6,000 or less in any six-month period, such as swapping boards, railing parts or stair treads. Joist, beam, post and ledger repairs are work on load-bearing supports, which SDCI says needs a permit no matter how small the job, and the usual exemptions do not apply in an environmentally critical area.
How much does waterproof deck repair cost?
Waterproof deck repair cost depends on how far the water got. Resealing a membrane seam, a door threshold or the ledger flashing is a contained repair, and deck repairs start at $199. If water has rotted the sheathing or framing under the membrane, that wood is replaced before the deck is re-sealed, so the job is priced in writing after the free inspection.
Why is my deck leaking into the room or garage below?
On a standard deck, most leaks come from ledger flashing that is missing, too short or laid over the house wrap instead of tucked behind it, so water runs behind the ledger and into the wall. On a deck over a living space or a garage, the membrane usually fails first at door thresholds, edges and posts that pass through it. Leaking deck repair opens that spot, replaces wet wood and re-seals it.
Get a Free Deck Inspection and Estimate
Call with what you found and have your photos ready. We check the boards, frame, posts and ledger on site for free and tell you whether a Seattle deck repair will hold or the deck needs a rebuild, with a written price before any work starts. Up to 25% off your deck project. Free on-site estimate, no obligation.
At the visit we probe the boards, joists, posts and ledger, check the flashing where the deck meets the house and tell you which parts of the frame can stay. When both a repair and a rebuild would work, we walk you through each option so the choice is yours. Talk to our deck contractors in Seattle before you decide.