Georgia enforces the 2024 International Residential Code with state amendments for one- and two-family homes, and Section R311.7 of that code sets the dimensions a set of deck stairs must meet before an inspector signs off. The numbers below are what building inspectors in Forsyth County and the surrounding counties check with a tape measure at the final inspection.
Riser Height And Tread Depth
The code caps riser height at 7 3/4 inches and requires a tread depth of at least 10 inches, measured from the nosing of one tread to the nosing of the next. The tolerance between the tallest and shortest riser in a single flight is 3/8 inch, and the same 3/8 inch limit applies to tread depth. Inspectors measure every riser because an uneven step is the most common cause of a trip on exterior stairs.
The total rise from the landing pad to the deck surface determines how many risers the stair needs. A deck that sits 36 inches above grade cannot be served by four risers, because 36 divided by 4 is 9 inches. It needs five risers at 7.2 inches each. A deck 48 inches off the ground needs seven risers, not six.
When tread depth is less than 11 inches, the code also requires a nosing that projects between 3/4 inch and 1 1/4 inches past the riser below it. Open risers are allowed on decks, but if the stair's walking surface is more than 30 inches above grade, the opening between treads cannot let a 4 inch sphere pass through.
Stair Width And Headroom
A deck stair needs a clear width of 36 inches measured above the handrail height. Below the handrail, the clear width can narrow to 31 1/2 inches with one handrail or 27 inches with handrails on both sides. Headroom is 6 feet 8 inches, measured vertically from a line connecting the tread nosings. Headroom rarely comes up on an open deck, but it matters on stairs that pass under a covered porch roof or a second-story deck.
Handrails And Guards
Handrails and guards are separate items in the code, and a deck stair usually needs both. A guard keeps people from falling off the side. A handrail gives them something to grip. The requirements inspectors check are:
- A handrail is required on at least one side of any stair with four or more risers
- Handrail height is 34 to 38 inches, measured vertically from the tread nosing
- The handrail must be graspable, either a round profile between 1 1/4 and 2 inches in diameter or a shaped profile with a finger recess, and it must run continuously from the top riser to the bottom riser with ends that return to a post or wall
- Guards are required wherever the deck or stair surface is more than 30 inches above grade measured within 36 inches horizontally, and guards along stairs must be at least 34 inches tall measured from the nosing
- Guard infill cannot allow a 4 inch sphere to pass through, and the triangle formed by the tread, riser, and bottom guard rail cannot allow a 6 inch sphere to pass through
A common failure is a 2x4 cap rail on top of the guard posts. It meets the guard height but is too wide to grip, so it does not count as a handrail. The stair still needs a separate graspable rail mounted below it.
Landings At The Top And Bottom
A landing is required at the top and bottom of every flight. The landing must be at least as wide as the stair and at least 36 inches deep in the direction of travel. On a deck, the deck surface itself serves as the top landing. The bottom landing is the part homeowners miss. Bare dirt or a single loose paver does not pass. A poured concrete pad or a properly set paver landing is the standard, and in North Georgia's red clay, a pad set on compacted gravel holds up better than one poured directly on soil that heaves and settles with rain.
The code limits a single flight to 12 feet 7 inches of vertical rise between landings. Second-story decks on sloped lots, which are common in Cumming and the lake neighborhoods around Lanier, often exceed that and need an intermediate landing. That landing has its own footings, posts, and guards.
Stringers, Footings, And Attachment
Stringers are the sawtooth-cut boards that carry the treads. They are cut from 2x12 pressure-treated lumber, and once the notches are cut, the remaining throat of the board is what carries the load. The prescriptive deck guide that Georgia inspectors reference limits a cut stringer to roughly 6 feet of horizontal span between supports. A longer run needs a post and beam under the middle of the stair.
Stringer spacing depends on the tread material. Pressure-treated 2x treads can span stringers set 16 inches apart. Composite stair treads cannot. Most composite manufacturers, Trex included, require stringers no more than 12 inches on center under stair treads, and some call for 9 inches when treads run on a diagonal. A composite deck with stairs framed at 16 inches will flex underfoot and will not meet the manufacturer's installation requirements.
The bottom of the stringers needs to bear on a footing or the concrete landing pad, not sit on grade. The top of the stringers attaches to the deck rim with metal stringer hangers or a ledger strip, not toe nails alone. Toe-nailed stringers are a frequent finding on decks that were built without a permit.
Lighting And Permits
The code requires exterior stairs to be lit at the top landing, with the switch inside the house. On a deck, that usually means a wall-mounted fixture at the door or a post cap light at the head of the stairs on a switched circuit.
Decks that attach to the house or stand more than 30 inches above grade require a building permit in Forsyth County and in the other metro counties. The inspection sequence covers footings before concrete is poured, framing before decking goes down, and a final inspection where the stair dimensions, handrails, guards, and landing are all measured. Local jurisdictions can adopt amendments on top of the state code, so the county or city building department is the authority on any specific project.
Deck Stairs Built To Pass Inspection
Forsyth Exteriors designs, builds, and repairs custom wood and composite decks in Cumming and across Forsyth County, and every stair the crew builds is laid out to the riser, tread, handrail, and landing dimensions above. Homeowners planning a multi-level deck or a raised deck on a sloped lot can schedule a free consultation with the custom deck builders at Forsyth Exteriors, and the team serving Cumming, GA will walk the site and plan the stair run before framing begins.
