How to Inspect Your Deck for Rot and Loose Fasteners (2024)

TL;DR: Push a screwdriver into your deck's ledger board, posts, and joists — if it sinks in more than a quarter inch without much resistance, you likely have rot. Check every fastener at the ledger board connection (the most common failure point in deck collapses) and tighten or replace anything loose. Do this once a year, ideally in spring before heavy summer use.

_Last reviewed: July 2026 · 7 min read_

You step out onto the deck for the first cookout of the year and wonder if that soft spot near the stairs is anything to worry about. It probably is. Deck failures are rarely sudden — they're the end result of moisture sitting in the same spot for years while nobody checked.

Okoniq Property Hub lets you log each year's deck inspection with photos and notes, so you can track whether that soft spot is getting worse or holding steady.

Where does deck rot actually start?

Deck rot almost always starts where wood meets moisture that can't escape — the ledger board (where the deck attaches to the house), post bases touching concrete or soil, and any spot where two pieces of wood sandwich together and trap water.

The ledger board deserves the most attention because it's structural and it's bolted directly to your house's rim joist. Water gets behind it through a failed or missing flashing, then soaks into both the ledger and the house framing without ever being visible from above. The Consumer Product Safety Commission has tracked deck collapses for years, and ledger board failure is the single most common cause. If your deck was built before 2000, there's a good chance it doesn't have proper flashing at all, since many older building codes didn't require it.

Post bases are the second trouble spot. Wood posts set directly in concrete, or resting on concrete without a metal standoff, wick up moisture constantly. Look for discoloration, a crumbly texture, or gaps where the post has shrunk away from its base connector. This is the same wicking behavior that shows up in downspout drainage problems near your foundation — water finds the path of least resistance and stays there until something rots or cracks.

How do you test for rot without tearing anything apart?

The screwdriver test is the standard method, and it costs nothing. Take a flathead screwdriver or an awl and press it firmly into the wood at a low angle, focusing on the ledger board, the base of every post, joist ends, and any spot with visible discoloration or mildew.

Solid wood resists the tool and you'll feel it stop after an eighth of an inch or so. Rotted wood lets the screwdriver sink in easily, sometimes an inch or more, with a soft or spongy feel instead of resistance. Do this test at least every foot along the ledger board and at the base of each post — rot doesn't spread evenly, so a solid spot six inches away doesn't mean the whole board is fine.

Pay extra attention after a wet spring or a winter with a lot of snow sitting on the deck. Moisture exposure is cumulative, and a deck that tested fine two years ago can have hidden rot now if drainage nearby has gotten worse. This is the same seasonal logic behind roofs aging faster than they should — sustained moisture exposure does more damage than any single storm.

What's the fastest way to check every fastener?

Walk the deck with a cordless drill or a wrench and physically test every bolt, lag screw, and structural screw you can reach, rather than just looking at them. A fastener can look fine and still be backed out a quarter turn, which is enough to let a board shift under weight.

Start at the ledger board bolts — these should be lag screws or through-bolts, never just nails, and every one should be snug against the wood with no gap. Move to the joist hangers next; each hanger should have every hole filled with the correct joist hanger nail or screw (not a random deck screw, which isn't rated for shear load). Then check the post-to-beam connections and the railing posts, since loose railing bolts are one of the more common injury-causing failures on older decks.

| Fastener Type | What to Check | Red Flag | |---|---|---| | Ledger board bolts | Snug, no gap, corrosion-resistant | Rust streaks, movement when pushed | | Joist hangers | Correct nails filling every hole | Missing nails, bent hanger | | Railing posts | Bolted through, not just screwed | Wobble when pushed sideways | | Deck boards | Screws flush, not popped up | Screw heads raised above board |

Any fastener showing rust streaks running down the wood below it is telling you moisture has been sitting there long enough to corrode metal, which usually means the wood underneath is compromised too.

When is loose or rotted enough to call a professional?

Call a licensed contractor if the screwdriver sinks in more than half an inch anywhere on the ledger board, a support post, or a beam — these are structural members and DIY patching isn't a safe fix. A single rotted deck board is a weekend repair; a rotted ledger board or post is not.

Also bring in a pro if you find the ledger board was attached with nails instead of lag bolts or structural screws, since this was common practice decades ago and is now considered inadequate by most current building codes. Same goes for decks over 10 feet high, decks that regularly hold more than a handful of people, or any deck attached to a house with visible gaps or water staining on the siding near the connection. The questions worth asking before you hire someone are similar across trades — the same due diligence covered in questions to ask before hiring a roofer applies here: ask about licensing, ask for references, and get the scope in writing before work starts.

If the issue is isolated to a couple of loose fasteners or one soft board, tightening or swapping in matching hardware is a same-day fix most owner-operators can handle with basic tools.

How does water end up under the deck in the first place?

Most deck moisture problems trace back to drainage, not the deck itself. Gutters and downspouts that empty near the deck's foundation posts keep the soil around them constantly wet, and that moisture travels up through end grain faster than most people expect. The same downspout mistakes that flood basements are often the reason a deck post rots from the bottom up years before the rest of the structure shows wear.

Check that downspouts discharge at least 5 feet from any deck support, and that the grade around posts slopes away rather than pooling. Fixing drainage is often cheaper than replacing a post, and it stops the rot from coming back after repair.

FAQ

How often should I inspect my deck for rot?

Once a year is the general standard, ideally in early spring before summer use ramps up. Decks over 15 years old or in wet climates benefit from a check twice a year, spring and fall.

Can I fix deck rot myself, or do I need a contractor?

A single rotted board or a loose railing bolt is a reasonable DIY fix with basic tools. Rot in the ledger board, support posts, or beams is structural and should go to a licensed contractor, since a mistake there affects the whole deck's safety.

What does deck rot look like before it's obvious?

Early rot often shows as slight discoloration, a dull or grayish patch, or a spot that feels slightly spongy underfoot before it's visibly crumbling. The screwdriver test catches this stage well before it's visible to the eye.

How long does a wood deck typically last before rot becomes a real issue?

Pressure-treated wood decks typically last 15 to 20 years before rot risk climbs significantly, though poor drainage or missing flashing can cut that in half. Composite decking resists rot in the boards themselves but the underlying wood frame still needs the same annual check.

Is it normal for deck screws to pop up over time?

Yes, this happens as wood expands and contracts with seasons, and it's usually cosmetic rather than structural. Re-drive or replace popped screws when you notice them so water doesn't collect in the resulting gap.

This is educational information, not engineering or safety advice. Call a licensed contractor or structural engineer if you find rot in a ledger board, support post, or beam, or if you're unsure whether your deck is safe to use.