8' x 20' Deck Material Calculator
A 160-square-foot elongated deck ideal for wrap-around designs or narrow side yards. Provides enough length for distinct dining and lounging zones arranged in a linear fashion. This 160 sq ft deck requires approximately 32 standard 5.5" x 12' pressure-treated boards, 7 joists, and 8 support posts.
Material Cost Comparison by Decking Type
The table below compares total material costs for a 8' x 20' deck across eight popular decking materials. All estimates use 16-inch joist spacing, perpendicular board pattern, railing on three sides, and one set of stairs. The structural framing (joists, beams, posts, concrete, hardware) is the same regardless of the surface decking material; only the board cost varies between options.
| Decking Material | Boards | Board Cost | Total Materials |
|---|---|---|---|
| Pressure-Treated Pine | 32 | $768 | $4,141 |
| Composite | 32 | $1,728 | $5,101 |
| Composite | 32 | $2,688 | $6,061 |
| Western Red Cedar | 32 | $1,728 | $5,101 |
| Redwood | 32 | $3,072 | $6,445 |
| Ipe Hardwood | 32 | $3,456 | $6,829 |
| Mahogany | 32 | $2,496 | $5,869 |
| PVC | 32 | $2,304 | $5,677 |
Complete Material Breakdown (Pressure-Treated Pine)
The following table provides a complete bill of materials for a 8' x 20' deck using pressure-treated pine 5.5" x 12' decking boards. This represents the most common and affordable configuration for residential decks of this size. Each line item includes the quantity needed and estimated cost at current retail pricing.
| Material | Specification | Quantity | Est. Cost |
|---|---|---|---|
| Decking Boards | 5.5" x 12' PT Pine | 32 boards (384 lf) | $768 |
| Joists | 2x10 pressure-treated | 7 joists (140 lf) | $224 |
| Beams | 2x10 doubled pressure-treated | 4 beams (64 lf) | $102 |
| Posts | 4x4 x 8' pressure-treated | 8 posts | $960 |
| Concrete | 60lb bags for footings | 16 bags | $96 |
| Deck Screws | #10 x 3" coated | 2 boxes (560 screws) | $110 |
| Hardware | Joist hangers & bolts | 7 hangers, 16 bolts | $66 |
| Railing | Posts, rails, balusters | 48 lf (9 posts) | $1,680 |
| Stairs | Stringers & treads | 3 stringers, 4 treads | $135 |
| Total Material Cost | $4,141 | ||
| Professional Labor Estimate (~$25/sq ft) | $4,000 | ||
Board Pattern Comparison
The board-laying pattern affects both the visual appearance of your deck and the amount of material needed. More complex patterns require additional waste allowance due to the angled and mitered cuts involved. The table below shows how pattern choice affects board count and decking cost for a 8' x 20' deck using pressure-treated pine.
| Pattern | Boards Needed | Linear Feet | Board Cost |
|---|---|---|---|
| Perpendicular (10% waste) | 32 | 384 lf | $768 |
| Diagonal (15% waste) | 33 | 396 lf | $792 |
| Herringbone (20% waste) | 35 | 420 lf | $840 |
Planning a 8' x 20' Deck
A 8' x 20' deck provides 160 sq ft of outdoor living space. At this size, you have room for a dining table that seats four to six people plus a separate seating area or grill station. Consider how traffic will flow between the house door and the primary seating area. Leaving a 3-foot-wide path for circulation prevents the deck from feeling cramped even when fully furnished.
For a deck of this size, the structural framework requires 7 joists (2x10 lumber, 140 linear feet total), 4 doubled beams spanning the 8-foot width, and 8 support posts set in concrete footings. Because the joist span is 20 feet, which exceeds 12 feet, 2x10 joists are recommended to prevent deflection and ensure a solid feel underfoot.
The total material cost for this deck ranges from approximately $4,141 using pressure-treated pine to $5,677 with premium decking materials. Professional installation adds approximately $4,000 at a typical rate of $25 per square foot. Many homeowners choose to DIY the construction to save on labor costs, which is feasible for experienced builders with this size deck, though permits and inspections may still be required by your local jurisdiction.
Frequently Asked Questions
How many boards do I need for a 8' x 20' deck?
For a 8' x 20' deck (160 sq ft), you need approximately 32 boards using standard 5.5" x 12' pressure-treated lumber with a perpendicular pattern (10% waste factor). If you choose a diagonal pattern, increase that to about 33 boards, or 35 boards for a herringbone pattern. The exact count varies by board length and width; longer boards mean fewer pieces but potentially more waste on cuts.
How much does a 8' x 20' deck cost to build?
Material costs for a 8' x 20' deck range from approximately $4,141 with pressure-treated pine to $5,677 with premium materials like ipe or PVC, including framing, hardware, railing, and stairs. Adding professional labor at approximately $25 per square foot brings the total installed cost to between $8,141 and $9,677 depending on material choice and local labor rates.
What joist size should I use for a 8' x 20' deck?
For a 8' x 20' deck with joists spanning 20 feet, use 2x10 joists at 16 inches on center. 2x10 joists are recommended because the span exceeds 12 feet. You will need 7 joists totaling 140 linear feet. Always use pressure-treated lumber for structural components and verify your local building code requirements.