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A 12x18 deck covers 216 square feet and costs about $3,802 – $5,940 installed in pressure-treated pine, up to $8,294 – $12,960 in composite. It takes about 29 decking boards at 20 ft, 14 joists, 4 footings and 42 linear feet of railing.
| Material | Installed cost |
|---|---|
| Pressure-Treated Pine | $3,802 – $5,940 |
| Cedar | $5,530 – $8,640 |
| Redwood | $6,566 – $10,260 |
| Composite (Trex/TimberTech) | $8,294 – $12,960 |
| PVC / Cellular | $10,022 – $15,660 |
| Ipe / Tropical Hardwood | $11,232 – $17,550 |
A 12x18 deck is 216 square feet. In pressure-treated pine, expect roughly $3,802 – $5,940 installed. Cedar runs about $5,530 – $8,640 and composite about $8,294 – $12,960. 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 12 ft direction, you need 26 rows — that is 468 linear feet of decking, or about 29 boards at 20 ft with a waste allowance. A 20 ft board crosses the deck in one piece, so there are no butt joints.
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.