Stud walls: the plus-one that everyone forgets
A wall of length L at spacing S needs L/S + 1 studs — the +1 is the stud at the far end, and forgetting it is the single most common framing miscount. On top of that comes a stud at each corner, extra studs for T-intersections, king and jack studs at every opening, cripples above and below, and the header itself. Plates are simpler: one bottom plate and usually two top plates, so plate length is roughly three times the wall length, in whatever stock lengths your supplier sells. Standard spacings are 16 in (406 mm) on centre in North America and 400 mm or 600 mm in metric practice — and 24 in centres are legitimate for non-load-bearing walls, saving real money on a large job.
Stairs: get the rise right and the rest follows
Divide the total floor-to-floor rise by a target riser height of around 180–190 mm (7–7.5 in) and round to a whole number of risers — you cannot have a fractional step, and every riser in a flight must be within a few millimetres of the others or it becomes a trip hazard. The number of treads is always one fewer than the number of risers. Codes then bound the geometry: the IRC caps risers at 7¾ in and requires treads of at least 10 in; UK Building Regs Part K allow a maximum 220 mm rise with a minimum 220 mm going, and a pitch no steeper than 42°. A useful cross-check is the old rule 2 × rise + going ≈ 600–640 mm.
Board feet, nominal sizes and what you actually get
Hardwood is sold by the board foot: thickness × width × length in inches, divided by 144, or a cubic foot of wood expressed as a 12 × 12 × 1 in board. The catch is that lumber is priced on its nominal size and delivered at its actual size — a 2 × 4 measures 1½ × 3½ in once it is planed, a 20% loss in section you must not carry into a strength calculation. Hardwood is graded in quarters: 4/4 is one inch rough, 8/4 is two inches. Buy 15–20% more board feet than your cut list demands, because grain, knots and defects mean you will not get every piece out of every board.
Decks and fences: the ground is the expensive part
Deck and fence estimates are dominated by what happens below the surface. A fence needs a post every 6–8 ft (1.8–2.4 m), and the number of posts is the number of bays plus one; each post hole is typically dug to a third of the post's above-ground height, and takes one to two 20 kg bags of concrete depending on hole diameter. Deck framing follows joist spacing — 16 in centres for most decking, 12 in for a diagonal lay — with beams and footings sized to the span. Decking boards themselves are a coverage problem: divide the deck area by the coverage of one board including its gap, then add 10% for cuts, and price the fasteners separately because hidden clips add up faster than anyone expects.
