Deck inspection checklist
An inspection is not a general assessment. It is a sequence of specific measurements and probes, done in a fixed order, against a fixed list. Knowing the order tells you what to fix first — and most failures are found in the first two items.
The order matters
- Permit and plans. What was approved versus what was built. Any change in size, height, or attachment is the first question.
- Ledger and flashing. Fastener type, diameter, spacing and pattern; flashing present and lapping correctly; siding held clear.
- Framing connections. Joist hangers with the correct nails, beam-to-post connection, blocking, rim joists.
- Footings and posts. Post base, wood-to-soil clearance, concrete visible, post size.
- Guard and stair dimensions. The tape-and-sphere part, which is where most failures happen.
- Decking and fasteners. Gaps, spacing, protruding fasteners, board condition.
- Lateral load. Whether the deck resists racking, and how.
The measurements, with the tolerance
| Check | Requirement | How it is measured |
|---|---|---|
| Guard height | 36″ min | Vertical from deck surface to top of guard |
| Guard openings | 4″ sphere | A 4″ ball tried at every opening, including corners |
| Stair triangular opening | 6″ sphere | Between tread, riser and bottom rail |
| Riser height | 7¾″ max | Every riser; variation between them is also checked |
| Riser consistency | ⅜″ max difference | Largest riser minus smallest, across the flight |
| Tread depth | 10″ min | Nose to nose, not including nosing overhang |
| Handrail height | 34–38″ | Above the nosing line |
| Handrail graspability | 1¼–2″ circle | Profile, by eye and by tape |
| Post clearance from grade | 6″ typical | Wood to soil, at the base |
| Deck board gap | ⅛″ min typical | Between boards, for drainage |
The riser consistency check is the one homeowners are most often surprised by. Four risers at 7″, 7″, 7¼″ and 7½″ all pass the individual maximum, but the ½″ variation between the first and last is a trip hazard and fails the ⅜″ rule.
What fails a deck that looks fine
- Hanger nails replaced with deck screws. Visible on inspection, and it voids the hanger's rating. Look at every hanger, not a sample.
- No flashing, or caulk instead of flashing. Not always visible from above, which is why the inspector looks at the siding line and probes the ledger's top edge.
- A guard attached to decking only. A post bolted through boards rather than into the frame moves under a 200 lb push, which is the test.
- Notching and hole drilling in joists. A notch in the middle third of a joist, or a hole near the top or bottom edge, can cut capacity by a third or more.
- Decay at the post base. A probe with a screwdriver at the soil line finds it long before it is visible.
- Missing lateral resistance. A deck with no diagonal bracing and no rated connection to the house can rack; some inspectors ask for the detail explicitly.
Walking an existing deck, in ten minutes
- Stand at the middle and bounce. A springy deck has an undersized joist or a long span.
- Push hard on a corner guard post. Movement at the base means the post is not connected to the frame.
- Look along the ledger from the end. A sag or a gap at the top edge means water has been getting in.
- Probe every post at the soil line with a screwdriver. Soft wood means replace, not repair.
- Try a 4″ ball at three or four guard openings, including any that were modified.
- Check the bottom of the stair stringers where they meet the ground.
- Look up at the joist hangers from underneath — this is where substituted fasteners show.
What a walk-around cannot find
- It does not replace your jurisdiction's checklist. Many building departments publish their own deck inspection form, and that is the document that matters.
- It does not cover structural evaluation. Whether a 20-year-old deck can take a hot tub is an engineering question, not a checklist item.
- It does not cover electrical or gas. Deck receptacles, lighting circuits and gas connections for grills are separate inspections with their own requirements.
Questions people actually ask
What do inspectors look for on a deck?
In order: the permit and what changed, the ledger and its flashing, hanger fasteners, post bases and wood-to-soil clearance, guard height and the 4″ sphere, stair riser consistency, and handrail graspability.
How much can riser heights vary?
A maximum of ⅜″ between the largest and smallest riser in a flight. Each riser must also be under 7¾″, so a flight can pass on height and still fail on consistency.
Can a deck fail inspection for using screws in hangers?
Yes. Hangers are rated with specific fasteners, and a deck screw has no published capacity in that connection. It is one of the most common failures because it is invisible from above.
How much clearance between wood and the ground?
Six inches is the common requirement at the base of a post, and girders and joists need more. The point is to keep the wood out of the splash zone, which is where decay starts.
How often should a deck be inspected?
Annually for a wood deck, and after any event that loads it unusually — a heavy snow, a flood, or a summer with a hot tub added. Most of the serious failures develop over years and are visible long before they fail.