Published August 13, 2026 · Updated August 23, 2026 · By Tupep
The difference is not price, it is flexibility
Comparisons between composite and wood usually stop at cost per foot and maintenance. When we are actually placing an order, the difference that matters is that wood forgives a bad number and composite does not. You can rip a wood board narrow, cut it anywhere and screw it anywhere. Composite comes in fixed lengths, often has a machined groove you destroy the moment you rip it, moves noticeably with temperature, and frequently wants closer joist spacing. Every one of those changes the takeoff.
Where the waste comes from
Waste percent = (lineal feet purchased minus lineal feet installed) / lineal feet installed x 100. Run that for each candidate stock length and the right order jumps out.
Worked example: 14 ft deep x 20 ft wide deck
Boards run the 20 ft direction, so each row is 20 ft long and the rows have to cover 14 ft, which is 168 in.
Grooved composite sets its own gap through the hidden fastener clip, commonly around 3/16 in. Board face is 5.5 in, so the module is 5.6875 in. Solve n x 5.5 + (n-1) x 0.1875 = 168: 5.6875n = 168.1875, so n = 29.57. Not a whole number.
- 29 rows = 29 x 5.5 + 28 x 0.1875 = 159.5 + 5.25 = 164.75 in, which is 3.25 in narrow.
- 30 rows = 30 x 5.5 + 29 x 0.1875 = 165 + 5.4375 = 170.44 in, which is 2.44 in wide.
With wood you rip the last board and move on. With grooved composite you cannot: the groove is what the clip grabs, so a ripped board needs face screws and a plug at the perimeter. The answer is to frame the deck to the board module. Build the frame at 164.75 in of deck surface, or 170.44 in, and the decking lands perfect with no rip anywhere. Deciding board width before framing width is the biggest planning difference between the two materials.
| Behavior | Wood decking | Composite decking |
|---|---|---|
| Rip to width | Anywhere, takes a screw fine | Loses the groove, needs face screw and plug |
| Stock lengths | 8, 10, 12, 16, sometimes 20 ft | Usually 12, 16, 20 ft only |
| Gap across the board | You choose, based on moisture | Set by the clip, typically about 3/16 in |
| Gap at butt ends | Small, wood shrinks in length very little | Per manufacturer chart, varies with install temperature |
| Joist spacing | Per code span tables | Per the product instructions, often tighter |
| Diagonal layout | Same joists, more cutting waste | Usually requires closer joist spacing |
Length choice and butt joints
With 29 rows at 20 ft each, you need 580 lineal feet installed.
- 20 ft stock: 29 boards, 580 ft purchased, zero waste, zero butt joints.
- 16 ft stock: each row is 16 + 4. Twenty nine 16-footers plus eight more cut into four 4 ft pieces each gives 37 boards, 592 ft purchased. Waste is 12 ft, or 2.1 percent, but you now own 29 butt joints.
On wood, 29 butt joints means 29 blocking locations. On composite it means 29 blocking locations and 29 thermal gaps to get right. Composite expands and contracts along its length far more than wood, so the gap at a butt end depends on board length and on how warm it is the day you install. Manufacturers publish a table for this as part of the installation instructions the warranty and code approval hang on. Use their number. We buy the 20 ft boards and delete the problem.
Joist spacing changes the framing order too
This is the one that catches people mid-project. Many composite products require joists at 16 in on center for a perpendicular layout and 12 in on center for a 45 degree diagonal layout, because a diagonal board spans a longer distance between bearing points. Some products want 12 in on center even perpendicular. Wood decking spacing comes out of code span tables; composite spacing comes out of the manufacturer’s instructions, which are typically referenced by the product’s code approval.
On our 20 ft wide deck, that is not a small change. At 16 in on center, 240 / 16 = 15 spaces, so 16 joists. At 12 in on center, 240 / 12 = 20 spaces, so 21 joists. That is five extra 14 ft joists, plus five more sets of hangers and hanger fasteners, plus another row of blocking. If you decide on diagonal composite after the frame is built, you are adding joists into an existing frame, which is miserable work.
Waste allowances by pattern
These are planning allowances to add to your net lineal footage, not precise figures.
| Pattern | Typical waste allowance | Why |
|---|---|---|
| Straight, stock length matches the run | 3 to 5 percent | Culls, splits, a bad end or two |
| Straight, stock length does not match | 8 to 12 percent | Cutoffs too short to reuse |
| Picture frame border | 10 to 15 percent | Miter cuts plus shortened field boards |
| 45 degree diagonal | 15 to 20 percent | Corner rows are short offcuts |
| Herringbone or inlay | 20 to 25 percent | Every board is a two-cut piece |
On the diagonal, the longest row across a 14 by 20 deck is the diagonal itself, the square root of (196 + 400), which is 24.4 ft. That is longer than any stock composite board, so the longest rows need a butt joint no matter what, right where the deck is most visible.
Two field notes
Composite is heavier and floppier than wood, and it takes a set. Do not leave a bundle on uneven ground in the sun for a week before install or you will fight a bow in every board. Stack it flat and supported.
Cut composite with a fine-tooth blade. Wood tolerates a framing blade and a rough cut hidden under a fascia. A rough cut in composite shows every time, because color goes all the way through on some products and only partway on others.
Related guides
- Deck Framing Lumber List for a 10×12 Deck
- How Many Deck Boards for a 12×16 Deck
- Picture Frame Border: Extra Boards and Blocking
- Fence Materials for a Quarter-Acre Backyard
Sources and Further Reading
Run your own numbers with the Deck Board Calculator, or browse every tool on the calculators index. Coverage figures and material constants are cross-checked against manufacturer technical data sheets before publication. See our Methodology page for how figures are selected and verified.
Planning estimate only. Results assume standard conditions and are intended for material planning. Verify against your product’s technical data sheet and your local building code before purchasing. Structural, electrical, and gas work should be specified by a licensed professional.
Last updated: August 23, 2026
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