Outdoor guide
Rotting deck boards: how to check for rot and when a deck is unsafe
By the Home Doctor team · Reviewed
Quick answer
Soft, spongy or crumbling wood on a deck is rot, and where it is matters more than how much. Push a screwdriver into the wood: if it sinks in more than about 1/4 inch or the wood comes out soft and crumbly, it's rotting. A few rotted deck boards are a DIY swap for $50 to $250. Rot in the ledger (where the deck attaches to the house), the posts or the joists is structural: keep people off and call a deck builder. Ledger failure is a leading cause of deck collapses. Gray, weathered wood that's still hard is fine.
- How urgent
- Fix soon
A few soft deck boards can wait a few weeks if you block them off, though rot spreads and a board can break underfoot. It becomes 'stop and call a pro now' if the ledger, posts, joists or railings are soft or loose, or the deck bounces, leans or pulls away from the house.
- DIY or pro
- DIY if handy
Probing for rot, cleaning and sealing, and replacing individual deck boards are handy-homeowner jobs. Joists, beams, posts, the ledger, stairs and railings hold people up: have a deck builder repair them, and expect a permit for structural work in many areas.
Stop and call a pro now if
- The ledger, a post, a beam or a joist is soft or rotting, or the deck is pulling away from the house: keep everyone off the deck and call a deck builder or structural engineer.
- The deck bounces, sways or leans, or a post is cracked or tilted: keep people off it until it's inspected.
- A railing or stair handrail is loose: don't lean on it, keep kids away from that side, and block it off until it's fixed.
Common causes and how to tell them apart
1. Rotting deck boards
- How to tell
- Soft or spongy spots underfoot, dark stains, deep cracks, or boards that flex or crumble at the ends and around screws. Worst in shade, under planters and where leaves pile up.
- What fixes it
- Replace the bad boards. If more than a handful are going, check the framing underneath before re-decking.
2. Rot in the joists or beams
- How to tell
- From underneath: dark, soft wood on the tops of joists under board seams, at joist ends, or where a beam sits on a post. A screwdriver sinks in easily.
- What fixes it
- A small rotted section can often be reinforced by sistering a new joist alongside it. Widespread rot means rebuilding the frame. A deck builder should judge which.
3. Rotting or loose ledger board
- How to tell
- The ledger is the board fastened to the house that the joists hang from. Soft wood, rust streaks or water stains on it or the house behind it, no metal flashing over the top, only nails instead of bolts, or a gap opening between the deck and the house.
- What fixes it
- A deck builder replaces the ledger with proper flashing and bolts or structural screws, and checks the house framing behind it. Ledger failure is a leading cause of deck collapses.
4. Rotting posts at ground level
- How to tell
- Soft, cracked or crumbling wood where posts meet the ground or sit in soil or concrete. The post may lean, or the deck may sag above it.
- What fixes it
- Replace the post with ground-contact rated lumber on a concrete footing, with a metal post base that keeps the wood off the ground. The deck has to be temporarily supported while it's done.
5. Loose or corroded fasteners and joist hangers
- How to tell
- Nails popping up, screws that spin, rust streaks, or metal joist hangers that are flaking, thinned by rust or missing nails. Common on older decks built with non-galvanized hardware.
- What fixes it
- Reset or replace popped fasteners. Replace corroded hangers and connectors with hot-dip galvanized or stainless steel ones rated for treated lumber, using the fasteners the hanger maker specifies.
6. Weathered but sound wood
- How to tell
- Gray, faded wood with fine cracks along the grain, but it feels hard and a screwdriver barely goes in.
- What fixes it
- Nothing structural. Clean it, let it dry, and apply a penetrating stain or sealer to slow cracking and water absorption.
Not sure which one you have?
Snap a photo. Home Doctor narrows it down, tells you how urgent it is, and prices the fix.
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What you can safely try first
- 1Keep people off any area that feels soft, bouncy or loose, and block it off.
- 2Do the screwdriver test: push a flat screwdriver or awl into the wood with firm hand pressure. Sound wood resists and splinters in long pieces. If the tip sinks in more than about 1/4 inch or the wood comes out soft and crumbly, it's rotting.
- 3Probe the deck boards, then go underneath with a flashlight and probe the ledger, the joist ends near the house, the tops of the joists under board seams, the beam, and each post at ground level.
- 4Check the ledger: look for bolts or lag screws rather than only nails, metal flashing over the top, and any gap between the deck and the house.
- 5Shake the railings and stair handrails, and look for posts that lean and joist hangers that are rusted or missing nails.
- 6Photograph what you find with something for scale, and note which areas are soft. A builder can quote faster from it.
When to call a pro
- Any soft or rotting wood in the ledger, posts, beams or joists.
- The deck bounces, sways, leans or has pulled away from the house.
- Railings or stairs are loose or wobbly.
- Joist hangers or other metal connectors are badly rusted.
- More than a handful of boards need replacing, or the deck is 20 or more years old.
What it costs
| Job | DIY parts | Pro, installed |
|---|---|---|
| Replace a few deck boards | $50–$250 | $300–$900 |
| Sister a rotted joist | Not recommended | $250–$800 per joist |
| Replace a rotted post (with new footing) | Not recommended | $300–$1,000 per post |
| Replace the ledger board (with flashing) | Not recommended | $1,000–$5,000+ |
| Replace the deck, pressure-treated wood | — | $30–$70 per sq ft |
| Replace the deck, composite | — | $50–$100 per sq ft |
Ballpark US ranges as of September 28, 2026. Your region, access and the specifics of your home can move these a lot. Get two or three quotes for anything over a few hundred dollars.
What to tell the pro
My [wood / composite] deck is about [age] years old and [height] off the ground. I found soft or rotting wood in [some deck boards / the joists / the ledger at the house / the posts at ground level], and the deck [feels solid / bounces / leans / has pulled away from the house]. The joist hangers are [fine / rusty], and the ledger is attached with [bolts / nails / I can't tell]. Is it worth repairing, or should it be replaced, and does your quote include the permit, haul-away of the old wood, and new flashing at the house?
Questions people ask
How do I know if my deck boards are rotting?
Push a flat screwdriver into the wood with firm hand pressure. Sound wood resists and splinters in long pieces. If the tip sinks in more than about 1/4 inch or the wood comes out soft and crumbly, it's rotting. Gray color and fine surface cracks on hard wood are normal weathering.
Is it safe to walk on a deck with rotting boards?
It depends where the rot is. A few soft deck boards can be blocked off until you replace them. If the ledger, posts, joists or beams are soft, or the deck bounces, leans or is pulling away from the house, keep everyone off it until a deck builder or structural engineer inspects it.
How much does it cost to replace rotted deck boards?
Replacing a few boards yourself usually costs $50 to $250 in lumber and screws, and a pro typically charges $300 to $900 for a small repair. Replacing a whole deck runs roughly $30 to $70 per square foot for pressure-treated wood and $50 to $100 per square foot for composite.
Can you replace deck boards without replacing the frame?
Yes, if the joists, beams, posts and ledger are sound. Probe them before you re-deck, because new boards on a rotting frame won't last. Many builders add joist tape over the tops of the joists when re-decking to help keep water out of the wood.
Get an answer for your house
Every house is different. A photo gets you the likely cause, how urgent it is, and a fair price, in about 30 seconds.
Diagnose it from a photoFirst diagnosis free. No account needed.
General guidance, not a substitute for a licensed professional who can see the problem in person. If you smell gas, see sparks or smoke, or anyone is hurt, leave the area and call 911.