Deck safety inspection checklist

What you need

A flathead screwdriver, a torch, a tape measure and twenty minutes. The screwdriver is the important one: sound wood resists the tip pushed firmly into it, and wood that has begun to rot internally takes it with almost no resistance long before the surface looks wrong.

1. The ledger — check this first

The connection to the house is where most collapses start, so it gets checked first and most carefully.

• Is there flashing visible above the ledger? If you cannot see any, assume water has been getting behind it.
• What is it fastened with? Hex heads in two staggered rows is right. A row of screw heads, nail heads, or fasteners in a single line is not.
• Probe the ledger, and the siding directly above it, with the screwdriver. Any give is serious.
• What is it fastened to? A ledger on brick veneer, stucco over foam, or a cantilevered floor is not attached to structure.

Any soft wood at the ledger, or a ledger fastened with screws or nails, means stop using the deck until it is assessed. The ledger guide covers what a correct connection looks like.

2. Posts at ground level

Probe each post at grade and for six inches above it, and look at what the post sits on. A standoff base holding the end grain clear of the concrete is right; a post sitting directly on concrete, or set into soil, is wicking water into its end grain permanently.

Also check that posts are plumb and that none has shifted off its footing. A post leaning even slightly means the footing has moved or the connection has failed.

3. Joists, beam and hardware

From underneath with the torch, look for dark staining along the tops of the joists, which means water has been sitting in the board gaps above. Look for any joist that has dropped out of line with its neighbours.

Then look at the metal. Rust streaks running down from a hanger mean the fasteners are corroding — commonly because plain zinc-plated fasteners were used against modern copper-based preservative treatment. Check that every hanger has a fastener in every hole; half-nailed hangers are extremely common and carry a fraction of their rated load.

Finally, check the beam sits on top of the posts on a rated cap rather than being bolted to their sides. Side-bolted beams are not wrong everywhere, but they depend entirely on the bolts and are far more sensitive to corrosion.

4. Railings and guards

Push hard on the top rail at every post — genuinely hard, because the code load is 200 pounds applied in any direction. Any flex at the base means the post connection is not doing its job, and railing post failures are a common cause of falls from decks.

Then measure. The guard should be at least 36 inches tall on a residential deck, and a 4 inch sphere should not pass through any opening in it. At the bottom of a stair guard, the triangular opening should not pass a 6 inch sphere.

5. Stairs

• Measure every riser. They should all be within three eighths of an inch of each other, and the bottom one is the usual offender.
• Check the stringers for cracks, particularly at the back of the notches where the throat is narrowest.
• Check what the bottom of the flight bears on. A concrete pad or footing is right; soil or a couple of loose pavers is not.
• Check the handrail: present on four or more risers, 34 to 38 inches above the nosings, continuous, graspable and returned at both ends.

6. The walking surface

Walk the middle of every span and feel for bounce, particularly anywhere that has changed since last year. Look for boards that are soft, split through, or cupped enough to hold water. Check the gaps are clear — packed gaps are the mechanism that rots the joists you just inspected.

If anything on this list came back soft, loose or measurably wrong, work out whether you are looking at a repair, a resurface or a rebuild using the repair or replace guide.