Deck safety

Guards. The 36-inch minimum height and the 4-inch sphere rule get most of the attention, but the failure mode is almost always the post attachment, not the post. Under the prescriptive guide, guard posts must be at least 4x4 nominal with an adjusted bending design value of at least 1,100 psi, must not be notched, and where hold-down anchors are used they must have a minimum allowable tension load of 1,800 pounds for a 36-inch guard. A notched post is a known weak detail.

Stairs. Maximum riser height is 7 3/4 inches, minimum tread width 10 inches, and neither risers nor treads may vary from one another by more than 3/8 inch. Stairs must be at least 36 inches wide. Any stairway with four or more risers needs a handrail on at least one side, mounted 34 to 38 inches above the tread nosings, graspable, and returned at each end. If the total vertical stair height exceeds 12 feet, an intermediate landing is required. Openings in required stair guards must not pass a 4 3/8-inch sphere; triangular openings must not pass a 6-inch sphere.

The ledger. This is the connection between your deck and your house and it is the connection that kills people when it fails. Siding must be removed before the ledger goes on, approved corrosion-resistant flashing is required at the connection, and the ledger must be a minimum nominal 2x8. Older homes with thin band boards, metal-plate-connected wood trusses, or I-joist floor systems may not accept a standard ledger attachment at all — in those cases a freestanding deck or a full plan submission is required.

Lighting. Stairways must have a light source at the top landing that illuminates all stairs and landings, switched from inside the house, though motion or timed switches are acceptable. It is a code item and also the practical difference between a deck you use after dark and one you don't.

How to choose

Check guard posts, not guard height

Height is easy to eyeball and rarely the failure. Notched posts, missing through-bolts, and undersized rim joists are what give way.

Measure your risers

Risers over 7 3/4 inches or varying by more than 3/8 inch are a trip hazard and a code failure. Both are measurable in two minutes.

Inspect the ledger behind the siding

If nobody can tell you whether the ledger was flashed, assume it wasn't. Rot repair runs $300 to $5,000 and ledger failure is catastrophic.

Look at fasteners for corrosion

Hardware must be galvanized or stainless, and within 300 feet of a saltwater shoreline it must be stainless grade 304 or 316. Rust streaks are a warning.

Hot tubs are outside the standard rules

Decks supporting large concentrated loads like hot tubs are beyond the scope of prescriptive deck design and need engineered framing.