Structural deck repair fixes the parts that carry a deck’s weight: the footings, posts, beams and joists, the ledger that ties the deck to your house, and the metal connectors that join them. A deck that sags, bounces, sways or pulls away from the wall has a problem somewhere in that frame, and in Seattle the repair is held to a stricter standard than the national code: every deck has to be designed for 60 pounds per square foot.
If your deck moves under your feet or has opened a gap at the house, keep people off it and call (206) 202-8768 for a free inspection.
This guide covers how a deck frame carries its load, what makes a deck sag, bounce or sway, how each structural repair is done to Seattle’s code, and when the work needs a permit or an engineer. Rot is the most common cause of frame damage here; our guide to rotted and leaking decks shows where it starts and when a rotted deck is worth repairing.
How a Deck Frame Carries the Load
Every deck passes its weight down the same chain. The boards sit on joists. The joists rest on a beam or hang from the ledger on the house. The beam sits on posts, and the posts stand on concrete footings in the ground. Structural repair is work on any link in that chain, or on the connectors that tie one link to the next.
- Footings: concrete pads or piers in the ground, sized for the deck area each one carries.
- Posts: the vertical members between the footings and the beam.
- Beams: the heavy members that carry the joists between the posts.
- Joists: the framing the deck boards are fastened to.
- Ledger: the board fastened to the house that carries the house side of the deck.
- Connectors: joist hangers, post bases, post-to-beam connectors, hold-downs, bolts and screws.
When one link fails, its load moves to the parts around it, so a footing that settles at one corner can crack a beam or pull hangers loose over a few winters. Boards, railing infill and stain are not structural; replacing them is regular deck repair.
Seattle’s 60-Pound Standard and Why Older Decks Fall Short
The SDCI deck page says Seattle requires every deck to be designed for a live load of at least 60 pounds per square foot. The deck section of the 2021 International Residential Code is built around 40. Washington’s own version of that section, WAC 51-51-0507, replaces the national tables for footings, posts, beams and joists with tables built for 60 pounds, so the same lumber spans less here than in a national span chart.
| Joist size | Washington (60 psf) | National code (40 psf) |
|---|---|---|
| 2x6 | 7 ft 1 in | 8 ft 4 in |
| 2x8 | 9 ft 5 in | 11 ft 1 in |
| 2x10 | 11 ft 6 in | 13 ft 7 in |
| 2x12 | 13 ft 4 in | 15 ft 9 in |
A deck framed from a national chart can have joists about 1 to 2 1/2 feet longer than Washington allows, and that extra length is the most common reason a deck feels springy. When a repair adds or replaces framing, the new members are sized from the Washington tables, the same tables the permit inspector works from.
Why a Deck Sags and How the Fix Works
A sag means something under the deck has dropped or bent, and where the dip is points to the part that failed. Near one post, look at that post and its footing. Between two posts, look at the beam. Across the middle of the joists, look at the joists.
- A footing that settled or was never deep enough. Deck footings have to be placed at least 12 inches below the undisturbed ground surface (Section R507.3.2) and be sized for the deck area they carry. On soil rated at 1,500 pounds per square foot, Washington’s table calls for a footing at least 18 inches square, or 20 inches round, and 6 inches thick under a post that carries 40 square feet of deck. A block resting on the surface, or a small footing under a large section of deck, sinks.
- A post too slender for its height. Washington’s post table limits a Douglas fir or hem-fir 4×4 that carries 120 square feet of deck to 4 feet 1 inch, measured from the top of the footing to the underside of the beam, and does not allow a 4×4 at 140 square feet or more. A 6×6 carrying the same 120 square feet can stand 13 feet 3 inches.
- A beam that is too small or not built as one piece. A beam sags when it spans farther than the table allows or overhangs a post by more than a quarter of its span. The plies of a built-up beam have to be nailed together with two rows of 10d nails every 16 inches along each edge (Section R507.5), and each end needs at least 1 1/2 inches of bearing on a wood post (Section R507.5.1).
- Rot at a post base or in the beam. Wet wood loses strength before it looks bad; the rotted deck guide shows where to check.
The repair starts with temporary shoring that carries the deck while parts come out. A failed footing is dug out and poured again at the size and depth the table calls for. A new post of the size the table allows goes on a metal post base, because a post on a concrete footing has to be held against sliding, either by a manufactured connector or by 12 inches of embedment (Section R507.4.1). A beam that is too small is replaced, or a new beam and footings are added to shorten its span. Each beam is fastened to its posts with connectors sized for both pieces, with washers under every bolt head and nut (Section R507.5.2), and the deck comes off the shores level.
Why a Deck Bounces and How to Stiffen It
Bounce comes from the joists. The span tables limit how far a joist may bend under a full load to 1/360 of its span, so a joist that is longer than the table allows, spaced too far apart or free to roll will flex when people walk on it.
- Joists longer than the Washington table. The fix is a sister: a new full-length treated joist fastened alongside each weak one. Where the spans are far over, a new beam on its own posts and footings under the middle cuts every span in half.
- Joists that can roll. The code wants something at the ends and bearing points of every joist that stops it from rotating: joist hangers, blocking at least 60 percent as deep as the joist, or a rim joist fastened to each joist end with at least three 10d nails (Section R507.6.2). Rows of blocking are added where they are missing.
- Missing or loose hangers. A joist that frames into the side of a beam or the ledger has to sit in an approved joist hanger (Section R507.6.1). Toenailed joists get hangers, and hangers missing nails are refastened.
- Boards that need closer joists. Joist spacing is also limited by the decking (Table R507.7). Some composite and PVC boards need joists closer together than the wood boards they replace, so the spacing is checked before a composite resurfacing.
A Deck Pulling Away From the House
The ledger has two jobs: it holds up the house side of the deck, and it keeps the deck from moving away from the wall. Nails do neither for long, and the code does not allow an attached deck to depend on toenails or nails that can pull out (Section R507.8).
- The ledger itself: at least a 2×8 of treated or naturally durable lumber (Section R507.9.1.1), fastened to the house band joist with hot-dipped galvanized or stainless lag screws or bolts at the spacing the code tables set (Section R507.9.1.3). The band joist has to bear fully on the house structure.
- No beams on the ledger: a ledger is not allowed to carry the concentrated load of a beam or girder; a beam needs its own posts.
- Hold-downs: to keep the deck from pulling away, the code ties the deck to the house framing with hold-down devices, either at least two within 24 inches of each end of the deck, each rated for 1,500 pounds, or at least four, each rated for 750 pounds (Section R507.9.2). Washington’s version adds that a deck no more than 30 inches above grade at any point may be left unattached.
Seattle adds that the ledger has to stay attached in an earthquake: SDCI points to the code’s prescriptive ledger connection or a design by an engineer. A deck with a gap opening at the house, ledger bolts working loose or a ledger that was only nailed is shored and refastened with new lag screws or bolts and hold-downs. If the ledger or the wall behind it has rotted, that repair is covered in our rotted ledger section.
A Wobbly or Swaying Deck
A deck that sways when people move on it is short on the connections that keep its parts from shifting sideways. The usual causes are posts toenailed to the beam with no connector, posts that sit loose on their footings, posts too tall and slender for the load and no lateral connection at the house.
The repair ties the frame together: a post-to-beam connector sized for both pieces at the top of every post, a post base at the bottom, larger posts where the table calls for them and hold-downs at the ledger. A deck taller than the code tables cover, or one that still sways after those connections are in, gets a design from a structural engineer.
Rusted Hangers, Bolts and Flashing
Treated lumber corrodes plain steel, and a hanger or bolt that rusts through drops its load onto whatever is next to it. The code requires deck fasteners and connectors to be hot-dipped galvanized to ASTM A153 or made of stainless steel, silicon bronze or copper (Section R507.2.3), and the flashing at the house to be corrosion-resistant metal at least 0.019 inch thick or an approved nonmetallic material (Section R507.2.4).
Rust streaks under hangers, bolts you can turn by hand and connectors that flake are replaced one connection at a time with the frame shored, so no part of the deck hangs on failing hardware while the work goes on.
Permits and Engineers for Structural Deck Repair in Seattle
Seattle lets small repairs go without a permit when the work costs no more than $6,000 within six months, counting labor and parts at fair market value even if you do the work yourself. Structural repairs are the exception: the SDCI permit guidance says any work on load-bearing supports needs a permit no matter how small, and none of these exemptions covers a property in an environmentally critical area. Replacing a footing, post, beam, joist or ledger is work on load-bearing supports.
Most structural repairs follow the code tables, and SDCI notes that deck drawings rarely need an architect’s or engineer’s stamp. An engineer comes in when a repair goes past the tables, such as a ledger connection that does not fit the prescriptive detail or posts taller than the table allows. A deck with beams 14 feet or longer is on Seattle’s list for the full addition or alteration permit rather than the simpler one; our Seattle deck permit guide lists all the thresholds.
When a Structural Repair Turns Into a New Frame
One footing, one post or a few joists is a contained repair. When the joists across the whole deck are over the Washington spans, several posts and footings are undersized and the ledger has no lateral connection, the repair reaches most of the frame, and building a new frame to the 60-pound tables is often the simpler job.
Deck repairs start at $199, and structural repairs are priced in writing after the free inspection. Our repair-or-replace guide walks through the decision, the Seattle deck cost guide has the price lines for a full deck replacement, and qualifying projects get up to 25% off.
What Happens During a Structural Deck Repair
- Free inspection. We check the footings, posts, beams, joists, ledger and hardware, and measure spans and post heights against the Washington tables.
- Written estimate. What failed, what the repair includes and who handles the permit.
- Permit. Filed before work starts when the repair touches load-bearing supports.
- Shoring. Temporary supports carry the deck while footings, posts or beams are replaced.
- Repair. New framing and code-rated connectors, then the boards and railing go back on.
- Inspection. When the work is permitted, the city inspects it before it is closed up.
Structural Deck Repair: Common Questions
What is structural deck repair?
Repair of the parts that carry a deck’s weight: the footings, posts, beams and joists, the ledger fastened to the house, and the hangers, post bases, bolts and hold-downs that connect them. Boards, railing infill and stain are surface work, not structural.
Why is my deck bouncy?
Usually because the joists span farther than Washington’s 60-pound tables allow, sit too far apart for the boards, or can roll because blocking or hangers are missing. Sistering new joists, adding blocking and hangers, or adding a beam under the middle stiffens the deck.
How do you fix a sagging deck?
Shore the deck, find the part that dropped or bent and replace it to the table: a deeper, larger footing, a heavier post on a metal base, or a larger beam or an added beam that shortens the span. Each beam is bolted to its posts with sized connectors before the shores come out.
Is a deck safe if it sways or is pulling away from the house?
Treat it as unsafe. Keep everyone off a deck that sways, has a gap opening at the house, or has a soft, leaning or loose post until the frame is checked. A deck inspection tells you which parts can stay and what has to be fixed first.
Do I need a permit for structural deck repair in Seattle?
Yes. Seattle exempts small repairs up to $6,000 within six months, but SDCI says any work on load-bearing supports needs a permit no matter how small, and the exemptions never cover a property in an environmentally critical area. Replacing a footing, post, beam, joist or ledger is that kind of work.
How deep do deck footings have to be in Seattle?
At least 12 inches below undisturbed ground (Section R507.3.2), and sized from Washington’s footing table for the deck area the post carries and the soil. On soil rated at 1,500 pounds per square foot, a post carrying 40 square feet of deck needs a footing at least 18 inches square or 20 inches round, and 6 inches thick.
Get Your Deck Frame Checked
Call our Seattle deck builders and tell us what you see: a dip, a bounce, a gap at the house or a post that has moved, and send photos if you have them. At the free on-site inspection we check the frame from the footings to the ledger, measure it against Washington’s tables and give you a written price for the repair before the work begins. Up to 25% off your deck project. Free on-site estimate, no obligation.