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A 20x24 deck covers 480 square feet and costs about $8,448 – $13,200 installed in pressure-treated pine, up to $18,432 – $28,800 in composite. It takes about 93 decking boards at 20 ft, 19 joists, 4 footings and 64 linear feet of railing.
| Material | Installed cost |
|---|---|
| Pressure-Treated Pine | $8,448 – $13,200 |
| Cedar | $12,288 – $19,200 |
| Redwood | $14,592 – $22,800 |
| Composite (Trex/TimberTech) | $18,432 – $28,800 |
| PVC / Cellular | $22,272 – $34,800 |
| Ipe / Tropical Hardwood | $24,960 – $39,000 |
A 20x24 deck is 480 square feet. In pressure-treated pine, expect roughly $8,448 – $13,200 installed. Cedar runs about $12,288 – $19,200 and composite about $18,432 – $28,800. Building it yourself typically removes 40 to 55 percent of those figures, because labour is around half of a finished deck price.
Laying boards across the 20 ft direction, you need 43 rows — that is 1032 linear feet of decking, or about 93 boards at 20 ft with a waste allowance. At 24 ft there is no stock length that crosses in one piece, so each row takes 2 boards with 1 butt joint that needs blocking beneath it.
About 4, one under each post, with posts at no more than 8 feet along the beam. That is roughly 0.49 cubic yards of concrete for 12 inch tubes poured 42 inches below grade — around 23 eighty-pound bags. Your own frost depth sets the real number and is not negotiable.