Deck Stair Stringer Replacement — Rotted or Undersized Stringers
The deck is fine. The stairs off it bounce, the bottom of the stringers is black and soft, and the top has pulled a gap from the rim. The stringers need to go; the rest can mostly stay.
Deck stair stringer replacement swaps the rotted or undersized sawtooth boards under your deck steps for new treated stringers, hung from the deck with hardware and landed on a pad or footings instead of dirt. JMB Builders does it across the Twin Cities metro, reusing sound treads and rails or replacing them, and adding a center stringer where the old spacing let composite treads sag. Priced per project, quoted from your photos within one business day.
- Priced per project; stringers, hangers and pad together
- Treads and rail reused when sound, replaced when not
- Center stringer added for composite or wide treads
- Quote from photos in 1 business day
- Licensed MN contractor BC809005
Stringers are the part of a deck stair nobody looks at until it fails. On most decks they were cut from treated 2x12, notched for the treads, nailed to the rim joist at the top and set on the grass at the bottom. Two things go wrong. The bottom rots because it is sitting in wet soil and frost moves it every year. And the notched stringers were spaced for wood treads, so when the deck got composite treads later, or the treads were long to begin with, the middle sags and the stairs bounce. Sometimes the cut left so little wood at the throat of each notch that the stringer was undersized the day it was built.
The good news is the stringers are usually the only thing wrong. The treads can be unscrewed and set aside. The rail posts and rail can be braced and kept, or taken off in one piece and put back. The deck rim they hang from is checked, because a stringer nailed to a rotted rim is the other half of this failure. Then new stringers go in with the parts the old ones were missing.
That means a solid attachment at the top, stringer hangers or a hanger board fastened to blocking behind the rim, not nails into the face. It means a landing that does not move: a poured concrete pad, precast pad blocks on compacted base, or frost footings with a post base on a tall stair, with the stringers held up off it. It means one more stringer than the old stairs had when the treads are composite or the stair is wide. The treads go back on, the rail goes back on with its posts anchored to the new stringers, and the stairs are solid underfoot again.
What you supply
- A photo of the stairs from the side showing the stringers, the bottom and what they sit on
- A close-up of where the stringers meet the deck, from underneath if you can get there
- The number of steps, the stair width, and whether the treads are wood or composite
- Whether you want to reuse the treads and rail or replace them at the same time
- Stain color if we are finishing new wood; staining is quoted as a separate line, or do it yourself once it dries
What JMB supplies
- Treads and rail removed and set aside, or hauled away when they are being replaced
- Check of the deck rim joist and blocking behind it, repaired or replaced where the old stringers let water in
- New treated stringers laid out for the existing rise and run, with a center stringer added for composite or wide treads
- Stringer hangers or a hanger board fastened to solid blocking at the deck, with hardware rated for treated lumber
- A poured pad, precast pad blocks on compacted base, or frost footings with post bases at the bottom, stringers held off the surface
- Treads and risers reinstalled with new fasteners, or new treads in the material you choose
- Rail posts anchored through the stringers and rim, rail reset so it does not move
- Cut ends and notches sealed before assembly
- Photos of the new framing in your job folder
- Staining of new wood on a return visit when you want it done, quoted as its own line
How it is priced: per project
Quoted in writing from your photos within one business day. What moves the number:
- Number of steps and width of the stair, which sets how many stringers
- Reusing treads and rail vs. replacing them
- Pad blocks vs. a poured pad vs. frost footings at the bottom
- Rot in the deck rim or blocking at the top that has to be repaired first
- Adding a center stringer or going to solid stringers with cleats for composite treads
- Stairs off a second-story deck, which are longer and need a landing
- Whether the stair has to be rerouted because the old bottom landed on a slope or a sidewalk
Count the steps and measure the stair width. With the side photo we can lay out the new stringers before we arrive and the quote is firm.
How long it takes
Stringers under a typical three-to-six-step deck stair, treads and rail reused: one day, plus a day for a poured pad to cure if that is the base. Add a day when the rim is rotted or the treads are being replaced too.
How your project works
- 1
Send photos, get a written quote
Send three photos of the space and a sentence about what you want. You get a clear, itemized quote within one business day. We only come out to measure first when the job needs a tape measure — no pressure, no games.
- 2
Pick materials, or bring your own
We help you choose profiles and materials that fit the house and the budget, or match your existing millwork exactly — or you buy the door or trim yourself and we install it. Everything is confirmed before the crew is scheduled.
- 3
Clean, precise installation
The crew shows up on time, protects floors and furniture, and installs with tight joints and consistent reveals. Photos of the finished work go in your job folder.
- 4
Walkthrough and invoice
We walk the finished work with you. If anything is not right, we fix it before we call the job done. Then one invoice, paid by check or direct deposit — no card fees, no payment links.
Situations and options
Stringers only, treads and rail reused
The treads and rail are sound. We take them off, replace the stringers, set a proper base and hang the top with hardware, then put everything back with new fasteners. The least expensive version and the most common.
Add a center stringer for composite treads
Composite treads on stringers spaced for wood sag in the middle and feel spongy. We add a stringer in the center, or replace all of them with closer spacing per the tread manufacturer, so the treads are solid end to end.
Stringers and new treads
The stringers are rotted and the treads are grey and checked or cupped. New stringers plus new treated, cedar or composite treads and risers, matched to the deck boards, with the rail reset.
Rotted rim at the top
The stringers were nailed to the rim and water ran down behind them for years. We cut out the soft section of rim, sister or replace it, add blocking, and hang the new stringers from it with hangers so the connection does not fail again.
Deck Stair Stringer Replacement — Rotted or Undersized Stringers: questions, answered
How do I know if my deck stair stringers need to be replaced?
Look at the bottom of each stringer where it meets the ground. Black, soft wood you can push a screwdriver into means the stringer is rotting from the base up. Stairs that bounce in the middle, treads that flex, or a gap opening between the top of the stairs and the deck rim are the other signs. Any one of those is a stringer problem, not a tread problem.
Can I keep the treads and railing when the stringers are replaced?
Yes, if they are sound. We unscrew the treads and set them aside, brace or remove the rail in one piece, replace the stringers, and put the treads and rail back with new fasteners. Composite treads almost always survive this. Old wood treads that are cupped or checked are worth replacing while the stairs are apart.
What should deck stair stringers sit on?
Something that does not hold water or move with frost: a poured concrete pad, precast pad blocks on a compacted gravel base, or frost footings with a post base on a taller stair. The stringers are held up off the surface on a treated kicker or post bases so the end grain stays dry. Grass and soil are what rotted the old ones.
How are deck stairs supposed to attach to the deck?
With hardware into solid framing: stringer hangers or a hanger board fastened to blocking behind the rim joist, not nails through the face of the stringer into the rim. Nails work loose as frost moves the bottom of the stairs, and that is why stairs pull away from decks. We add the blocking and hangers as part of every stringer replacement.
Why do my composite deck stairs feel spongy?
Composite treads need stringers spaced closer together than wood treads, and most older stairs were built for wood. When the treads were swapped to composite the middle started to sag. Adding a center stringer, or replacing the stringers with closer spacing per the tread manufacturer, fixes it. Rotted stringers can also cause it, so we check both.
Do you fix the deck railing on the stairs too?
We reset the existing stair rail and anchor the posts through the new stringers and the rim. If the rail itself is loose, rotted or missing balusters, that is its own repair and we quote it alongside; see the deck railing repair page. Staining new wood is a separate line for a return visit once it has dried.
Recent JMB work, from our job log
59 installs recorded across 30 Twin Cities communities since Dec 2025. Window and door installs for homeowners and for the builders and dealers we sub for. Counts come straight from our job log; no customer names.
Get a written quote for this job
Three photos and a sentence is enough. You hear back within one business day. Or text the photos to 763-204-2099.
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Read morePage reviewed September 27, 2026 · JMB Builders LLC, MN license BC809005 · All exterior trim pages
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