Builds stairs, decks and specialized structures
The final domain covers stairs, decks and structures outside standard framing. Questions test stair geometry, the connections and footings that keep a deck attached and frost-free, and code limits for guards and handrails.
Stair geometry
Total rise is measured finished floor to finished floor. Choose a unit rise inside the code, divide, round to a whole number of risers, then recompute the exact unit rise - every riser must be identical. Treads number one fewer than risers. The comfort rule, 2R + T, commonly falls between 550 and 700 mm. Nosing projects past the riser, headroom is kept clear, handrails sit about 865–965 mm above the nosing line, and guards near 1070 mm with openings that will not pass a 100 mm sphere.
Decks
Footings go below frost depth or onto engineered pads. The ledger is fastened to the rim board or blocking with the specified structural screws or through-bolts - not to siding and not with nails alone - and is flashed so water cannot sit behind it. Joists hang in hangers, lateral bracing resists the deck pulling away from the house, and guard posts connect to the framing, not just the decking.
Specialized structures
Ramps follow a slope near 1:12 with landings; curved and spiral stairs carry their own code limits on tread and rise; timber frames rely on joinery sized by design. Stringers are laid out by stepping off the unit rise and run with stair gauges on a framing square, and the stringer is dropped by one riser thickness so the top tread finishes level with the floor.
Worked example
Total rise 2.79 m, target unit rise about 185 mm. 2790 ÷ 185 = 15.08, so use 15 risers: 2790 ÷ 15 = 186 mm. With a 250 mm run there are 14 treads, so total run = 14 × 250 = 3500 mm. Check 2R + T = 2(186) + 250 = 622 mm, inside the 550–700 mm band. Stringer length = √(2790² + 3500²) = √20,034,100 ≈ 4476 mm, so 4.8 m stock is needed.
Traps
Counting treads as equal to risers; forgetting to drop the stringer by one riser; bolting a guard post only through the decking; and setting a footing above frost depth.