Materials for a 16×20 Deck
Free calculator with pre-filled dimensions • Updated March 2026
A 16×20 deck (320 sq ft) is a large project needing ~95 decking boards (5.5" wide, 12 ft long with 10% waste), 13 joists, and 8 posts — $1,800–$3,500+ in materials.
Open calculator with these dimensions →16×20 Deck: Large Deck Material Guide
A 16×20 deck provides 320 square feet of outdoor living space — room for a full outdoor kitchen, dining set, lounge furniture, and circulation space. This is a significant construction project that typically requires a building permit and may benefit from professional help.
Material Summary
| Component | Qty | PT Pine | Composite (Trex) |
|---|---|---|---|
| Decking (5/4×6×20') | 28 | $560–$840 | $1,400–$2,100 |
| Joists (2×10×16') | 16 (16" OC) | $320–$448 | $320–$448 |
| Beam (LVL or 3-ply 2×12) | 20 ft | $120–$200 | $120–$200 |
| Posts (6×6×8') | 6 | $120–$180 | $120–$180 |
| Hardware + screws | — | $250–$375 | $350–$500 |
| Footings (sono tubes) | 6 | $120–$240 | $120–$240 |
| Railing (36" code) | 52 linear ft | $500–$800 | $1,000–$2,000 |
PT pine with railing: $1,990–$3,080. Composite with railing: $3,430–$5,670.
Pro Tips
- An engineer may be required. At 320 sq ft, many jurisdictions require engineered drawings for the permit. Budget $300–$500 for stamped deck plans — they ensure proper footing sizes and beam specifications.
- Sono tube footings are required at this scale. Deck blocks are not sufficient for a 16×20 structure. Pour concrete footings below frost depth with Simpson post bases. Footing diameter is typically 16–18 inches.
- Consider composite at this investment level. The additional $1,500–$2,500 for composite decking is easier to justify on a $5,000+ project. Composite requires zero staining/sealing and lasts 25–50 years vs. 10–15 for untreated wood.
Frequently Asked Questions
How much does a 16×20 deck cost?
DIY with PT pine and railing: $2,000–$3,100 in materials. Composite: $3,400–$5,700. Professional build with composite: $8,000–$15,000+ depending on height, railing style, and features.
Do I need an engineer for a 16×20 deck?
Many jurisdictions require engineered drawings for decks over 200 sq ft. Even where not required, an engineered plan ($300–$500) ensures proper footing, beam, and joist sizing and expedites permit approval.