Joist & Substructure Repair
The deck that has flexed underfoot in the same three spots for two summers. The board near the steps that the homeowner has been stepping around since last spring. The joist hanger that has been rusting through quietly under the deck because the original installer used the wrong galvanization grade for ACQ-treated lumber. The rim joist behind the ledger that has been soaking water through reversed flashing for ten years and finally went soft at the corner. Joist and substructure repair is the trade for what is failing one layer below the surface — sister-up of rotted joists with matched dimension stock, Simpson ZMAX or stainless hanger replacement where the original hangers have rusted through, rim-joist inspection at the ledger, and beam and post check from below. From $1,500 for a single-joist sister-up to $6,000 for a multi-joist substructure rebuild with hanger replacement and rim inspection. Honest scope — when the failure crosses into full re-frame territory or the rim joist behind the ledger is involved (meaning the deck-to-house connection has to come apart), we route the structural portion to a licensed Washington L&I general contractor with engineer sign-off and a permit, and Handis returns for the finish carpentry after the structural work closes.
Service
How Joist & Substructure Repair Works
Seven sequential steps from the under-deck inspection through the sister-up, hanger replacement, rim check, and the finish carpentry — the sequence we follow on every joist and substructure repair.
Under-Deck Inspection from Below with Headlamp and Awl
We walk the full underside with a headlamp, awl probe every accessible joist for soft punky wood, take moisture meter readings on the rim joist and at every joist-to-ledger connection, visually inspect every joist hanger for rust-through, and check beam-to-post connections. Most joist failures start at the rim or the hanger and are invisible from the deck surface above.
Identify Failed Joists by Probe and Meter
Healthy pressure-treated joists read 8 to 14 percent moisture and bounce the awl. Failing joists read above 20 percent at the rim, are soft to the awl, and dark at the failed end. We map the failures — rim-end, hanger-zone, or mid-span over a chronic-moisture spot — and quote the sister-up scope before any tool comes off the truck.
Source Matched Dimension Stock and Structural Screws
Matched 2x8 or 2x10 pressure-treated to the existing joist, GRK RSS or FastenMaster LedgerLOK structural screws in the size matching the joist depth, Simpson ZMAX replacement hangers in the matching depth and joist width. Materials are sourced before the visit so the work is one trip, not two.
Sister-Up with Full-Span Bearing on Both Ends
The new sister joist fastens to the failing joist with structural screws in a staggered pattern, full-shank pre-drilled where the joist depth requires it. The sister spans 24 inches minimum beyond the visible rot in each direction, into solid bearing on both ends (typically ledger-to-beam or beam-to-rim). We do not stop short of the rot propagation zone.
Replace Failed Simpson Hangers with ZMAX or Stainless
Failed galvanized hangers come out (cut where the original nails are corroded beyond extraction), the joist gets supported temporarily, the new ZMAX or stainless hanger goes in with Simpson SDS structural screws driven through the new hanger into both the ledger and the joist. We do not re-use a rusted hanger or patch it with extra nails.
Rim-Joist Inspection at the Ledger Connection
We probe the rim joist through the ledger lag holes (or pull a small siding section directly when access allows), moisture-meter the rim wherever reachable, and document the condition. If the rim is sound, we close the inspection. If the rim has gone soft, we route to a licensed Washington L&I GC for rim-joist replacement and stay in the project for the finish work after.
Beam and Post Visual Check from Below
Every visible beam-to-post connection gets a visual check for splitting, rotation, or visible separation. Post bases checked for ground contact and bottom rot. Post tops checked for fastener integrity. Visibly failed beam or post routes to its own scope (post replacement, beam sistering, or full re-frame); we report and quote the follow-up.
Document the Work and Hand Off to Finish Carpentry
Photos before-and-after of every sister joist and every replaced hanger, written notes on the rim and beam condition, recommended sequence for any follow-up scope (board replacement above the repaired joists, staining once the carpentry has settled). One-year project warranty on the sister-up and hanger work.
Joist & Substructure Repair Pricing
Final pricing depends on the number of failed joists, the joist depth, the number of failed hangers, the rim-joist condition, and whether the scope crosses into permit-required full re-frame territory. Rim-joist replacement at the ledger requires a licensed Washington L&I GC with engineer sign-off; that portion is quoted as a pass-through with the GC and engineer fees named line by line. Request a free estimate for an accurate quote.
Send us photos from under the deck (flashlight on the joist hangers and the rim) — we will quote the sister-up.
Why Handis for Joist & Substructure Repair
Most deck joist failures we find started ten or twelve years ago and only became visible last summer. The original builder used the wrong galvanization grade for ACQ-treated lumber (a known issue since the post-2004 standard change but routinely missed by deck builders well into the 2010s) — the joist hangers have been quietly rusting through ever since. The ledger flashing was installed reversed or never installed at all — the rim joist behind the ledger has been wicking water for a decade. The joist over the chronic-shade north corner never dried out after winter — the rot has propagated 3 feet inward from the rim. None of this shows up on the deck surface until a board flexes underfoot. The inspection from below is the only honest way to know what stage the substructure is actually in.
Estimate
Tell us where the deck is flexing (specific spots, near the rail, near the stairs, near the ledger), how long it has been happening, what you can see from the deck surface (board sag, separation, fastener pop), and what you can see from below if you have looked (visible rot, rusted hangers, soft spots). Flashlight phone photos from underneath are gold — joist hangers, the rim, beam tops, post bases. We will tell you on the response whether the visit is a single-joist sister-up, a multi-joist rebuild, or a scope that crosses into permit-GC territory, and quote each portion line by line.
Customer Reviews
Recent joist and substructure repair reviews from verified Handis customers.
12-year-old pressure-treated deck off our Renton split-level had two soft spots and the surface boards near the steps flexed underfoot. Handis tech went under with a headlamp, found three joists had gone soft at the rim end and 11 hangers had rusted through. Sistered up three joists with matched 2x10, replaced the failed hangers with Simpson ZMAX, was honest that the rim was still solid (which saved us a much bigger scope). Two visits. Deck has not flexed since.
Cedar deck on our 1998 Bellevue craftsman had a chronic soft spot in the north-shade corner. Tech awl-probed every joist in the bay, found the corner joist was soft for about 5 feet in from the rim. Sistered up a fresh pressure-treated 2x8 extending well past the visible rot, replaced two hangers, and explained that the chronic shade was driving the rot and a gutter extension above might help slow the next failure. Honest, surface-deep work.
We bought a 2003 house with a deck the inspector flagged as questionable. Handis came for the inspection visit, went under with a headlamp, identified the original deck builder had used the wrong galvanization for ACQ lumber and 14 hangers were rusting through. Did the hanger-only visit — replaced all 14 with ZMAX, also tightened a couple of beam-to-post bolts that had loosened. Deck has held three years since with no further issues.
Big multi-joist scope on a 2005 deck off our Kirkland house. Rim-joist inspection at the ledger came back showing the rim had gone soft behind the flashing for about 6 feet. Handis was honest that the rim replacement crossed into permit-GC territory, named a licensed Washington L&I GC, the GC came in for the rim and the engineer-stamped sign-off, then Handis returned to sister up four joists and replace nine hangers. Took five weeks total. Coordinated cleanly.
Smaller scope on our 2010 pressure-treated deck — one joist had failed at the mid-span over a chronic-moisture zone (we had a roof leak above the deck that was fixed years ago but the joist never recovered). Tech sistered up the failed joist with matched 2x10 fully spanning the rot into solid bearing on both ends, replaced two hangers in the affected bay. Honest, focused work — did not try to upsell anything outside the scope.
Frequently Asked Questions
Common questions about Handis joist and substructure repair — pricing, sister-up scope, hanger replacement, rim inspection, and the GC handoff for re-frame work.