SIDING

Measure the gross exterior wall area of the house. The simplest approach: measure perimeter × wall height for the rectangular portions. For gable ends (the triangular wall portions under a roof slope), measure the gable height × half the wall width and add. For multi-story houses, measure each level separately and sum.

Subtract the area of windows and doors from the gross — a standard window is 12–15 ft², a 6-foot patio door is 42 ft², a single entry door is 21 ft². The calculator subtracts openings, applies a 10% waste factor, and returns squares (1 square = 100 ft²) — the standard unit siding is sold by at home centers and lumberyards.

For a 2-story 24 × 32 ft house with 9-foot wall heights, six 15 ft² windows, and one 21 ft² entry door:

Perimeter = 2 × (24 + 32) = 112 ft. Wall area = 112 × 9 × 2 (two stories) = 2,016 ft². Subtract gables and windows.

Gable area (4/12 pitch): for a 24-ft gable, peak height = 24 × (4/24) = 4 ft. Gable triangle area = ½ × 24 × 4 = 48 ft². Two gables = 96 ft². Total gross wall area = 2,016 + 96 = 2,112 ft².

Openings: 6 × 15 + 21 = 111 ft². Net wall area = 2,001 ft².

Squares with 10% waste: 2,001 ÷ 100 × 1.10 = 22 squares.

At $200–$400/square for vinyl or $500–$900/square for fiber cement, materials run $4,400–$19,800. Trim, j-channel, corner posts, and starter strip add another $500–$1,500.

Forgetting the gable ends. A typical house has 50–150 ft² of gable wall hidden in the slope — easy to miss when eyeballing from the ground.

Underordering trim. Vinyl trim (j-channel, corner posts, starter strip) is sold separately from the siding squares and adds 15–25% to the materials budget. Easy to forget when costing a project.

Skipping house wrap. Code requires a weather-resistant barrier behind siding. House wrap (Tyvek or equivalent) costs ~$0.20/ft² and is the cheapest insurance against bulk water intrusion.

Mixing siding lots on visible elevations. Vinyl color shifts slightly between lots. Order all your siding from a single batch at the start; if you need a partial reorder, save it for the back wall where mismatches are less visible.

1 square = 100 ft² of finished wall. All siding is sold by the square.

Standard window: 12–18 ft². Patio door: 40–50 ft². Entry door: 20–22 ft².

Gable area = ½ × wall width × peak height. Peak height = wall width × (pitch ÷ 12) for symmetric gables.

10% waste covers cuts and trim. Bump to 15% for staggered or shake-style profiles.

Vinyl runs $200–$400/square installed. Fiber cement (HardiePlank) runs $500–$900/square installed and lasts 2–3× longer.