# Deck joist spacing and how far deck joists can span Joist spacing from Trex, TimberTech, and Fiberon, DCA 6 Table 2 joist spans and overhangs, angled decking, blocking, and a joist lumber count. Guide page: (published 2026-10-06, updated 2026-10-06). This Markdown version has the guide's key points, outline, FAQs and sources; the full article, with its worked examples and diagrams, is on the page. ## Key takeaways - With boards square to the joists, Trex, TimberTech, and Fiberon all list 16 in on center for residential decks; Trex's 2×6 boards and TimberTech's Advanced PVC MAX boards allow 24 in. - Angled boards need closer joists: TimberTech requires 12 in on center for all angled installations, Fiberon lists 12 in for diagonals up to 45°, and Trex takes 4 in off its chart at 45°. - In DCA 6 Table 2 (40 psf live load, No. 2 grade), a 2×8 at 16 in on center spans up to 11 ft 10 in in Southern Pine and 11 ft 1 in in Douglas fir-larch, hem-fir, or spruce-pine-fir. - Span is measured between the faces of the supports and does not include the overhang, which is limited to the lesser of the table's overhang and a quarter of the actual span; DCA 6 limits joist length to 18 ft. - Closer spacing costs lumber: along a 16 ft ledger, joists at 12 in on center take 17 joists instead of 13. ## In this guide 1. [Joist spacing vs. joist span](https://www.howmanyyardsdoineed.com/guides/deck-joist-spacing-and-spans/#spacing-vs-span) 2. [Joist spacing by decking type](https://www.howmanyyardsdoineed.com/guides/deck-joist-spacing-and-spans/#spacing-by-decking) 3. [Diagonal decking needs closer joists](https://www.howmanyyardsdoineed.com/guides/deck-joist-spacing-and-spans/#diagonal-decking) 4. [How far deck joists can span (DCA 6 Table 2)](https://www.howmanyyardsdoineed.com/guides/deck-joist-spacing-and-spans/#span-table) 5. [Blocking between joists](https://www.howmanyyardsdoineed.com/guides/deck-joist-spacing-and-spans/#blocking) 6. [Worked example: joists for a 16 × 12 ft deck](https://www.howmanyyardsdoineed.com/guides/deck-joist-spacing-and-spans/#worked-example) 7. [Before you build or order](https://www.howmanyyardsdoineed.com/guides/deck-joist-spacing-and-spans/#before-you-build) ## Frequently asked questions ### How far apart should deck joists be? It depends on the decking. For residential decks with the boards square to the joists, Trex lists 16 in on center for its 1 in boards and 24 in for its 2×6 boards, TimberTech says never more than 16 in (24 in for its Advanced PVC MAX boards), and Fiberon lists 16 in for its composite boards. ### How far can a 2x8 deck joist span? In the American Wood Council's DCA 6 Table 2, a No. 2 Southern Pine 2×8 spans up to 13 ft 1 in at 12 in on center, 11 ft 10 in at 16 in, and 9 ft 8 in at 24 in. Douglas fir-larch, hem-fir, and spruce-pine-fir 2×8s span 12 ft 6 in, 11 ft 1 in, and 9 ft 1 in. Your local code has the final say. ### How far can a 2x10 deck joist span? DCA 6 Table 2 lists 16 ft 2 in, 14 ft, and 11 ft 5 in for a No. 2 Southern Pine 2×10 at 12, 16, and 24 in on center, and 15 ft 8 in, 13 ft 7 in, and 11 ft 1 in for Douglas fir-larch, hem-fir, and spruce-pine-fir. The span is measured between the faces of the supports, not including any overhang. ### What joist spacing do I need for diagonal decking? Use your decking maker's rule. TimberTech says all angled installations need joists 12 in on center at most and that more severe angles may need closer spacing; Fiberon lists 12 in for diagonals up to 45 degrees; Trex takes 2 in off its chart at 60 degrees and 4 in at 45 degrees, and halves it at 30 degrees. ### How far can deck joists overhang the beam? Under DCA 6, joists may extend past the beam face by the lesser of the Table 2 overhang and one quarter of the actual joist span, with blocking between the joists at the beam. For a Southern Pine 2×10 at 16 in on center, the Table 2 overhang is 3 ft 5 in. ### Do deck joists need blocking? DCA 6 requires blocking between joists at the beam where joists overhang it. Some decking makers want more: TimberTech's Advanced PVC guide requires rows of solid wood blocking between joists at most every 4 to 6 ft, and Fiberon recommends ladder-style blocking rather than blocking laid flat. ## Related calculators and guides ### Calculators - [Deck Calculator](https://www.howmanyyardsdoineed.com/deck-calculator/) — Decking board count from deck size, actual board width, gap, and board length, with the cutting assumptions shown. - [Board Foot Calculator](https://www.howmanyyardsdoineed.com/board-foot-calculator/) — Board feet per piece and in total from thickness, width, length, and quantity, with optional cost at your price per board foot. ### Guides - [Deck board spacing and layout: gaps, direction, and joints](https://www.howmanyyardsdoineed.com/guides/deck-board-spacing-and-layout/) — Side and end gaps, board direction, joint placement, and last-board planning from Trex and American Wood Council guides. - [Nominal vs. Actual Lumber Sizes](https://www.howmanyyardsdoineed.com/guides/nominal-vs-actual-lumber-sizes/) — A chart of real lumber dimensions from the national standard, dry versus green sizes, lengths, and board feet. ### Buying guides - [Best Cordless Circular Saws for Decking and Framing (2026)](https://www.howmanyyardsdoineed.com/best/cordless-circular-saws-for-decking/) — Six cordless circular saws ranked on published cut depth, bevel, brake and battery for cutting deck boards, joists, posts and stair stringers. - [DEWALT vs Milwaukee Drill/Driver Kits Compared (2026)](https://www.howmanyyardsdoineed.com/best/dewalt-vs-milwaukee-drill-driver-kits/) — Seven 20V MAX and M18 drill/driver kits side by side on their makers' published specs, ranked for deck, drywall and fence work, with screw counts per job. ## Sources - [DCA 6: Prescriptive Residential Wood Deck Construction Guide (based on the 2015 IRC): joist size, Table 2 spans and overhangs](https://web-media.awc.org/wp-content/uploads/2022/02/17210514/AWC-DCA62015-DeckGuide-1804.pdf) — American Wood Council. Used for: Table 2 spans and overhangs for No. 2 2x6–2x12 at 12, 16 and 24 in on center; overhang ≤ lesser of LO or L/4; joist length limited to 18'-0". Checked 2026-10-06. - [DCA 6: Prescriptive Residential Wood Deck Construction Guide (based on the 2015 IRC): decking requirements](https://web-media.awc.org/wp-content/uploads/2022/02/17210514/AWC-DCA62015-DeckGuide-1804.pdf) — American Wood Council. Used for: 2 in nominal dimension lumber or span-rated decking (usually rated 16 or 24 in); 2-8d threaded nails or 2-#8 screws per joist; perpendicular to 45° to the joists; at least 3 joists. Checked 2026-10-06. - [Trex Decking Installation Guide (2024): joist spanning for decking](https://images.trex.com/is/content/trexcompany/2024_Trex_Decking_Installation_Guide(update)pdf) — Trex Company. Used for: Residential: 16 in on center for 1 in and .875 in Select boards, 24 in for 2x6 boards; 2 in less at 60°, 4 in less at 45°, half at 30°; at least 3 joists. Checked 2026-10-06. - [TimberTech Composite and Specialty Decking: Decking Installation & Maintenance Guide](https://assets.timbertech.com/content/dam/document-library/TimberTech/installation-guides/decking/TimberTech-Composite-Installation-Guide-ENG.pdf) — TimberTech (AZEK Building Products). Used for: Joists 16 in on center maximum; 12 in maximum for all angled or commercial installations; blocking between joists every 4–6 ft for best results; 6–8 in maximum near glass and high heat. Checked 2026-10-06. - [TimberTech Advanced PVC Decking: Decking Installation & Maintenance Guide (rev. 07/26)](https://assets.timbertech.com/content/dam/wp-content/TimberTech-Advanced-PVC-Decking-Installation-Guide_ENG.pdf) — TimberTech (AZEK Building Products). Used for: Joists 16 in on center maximum (24 in for MAX boards); 12 in maximum for all angled or commercial installations; solid wood blocking required in rows at most every 4–6 ft. Checked 2026-10-06. - [Fiberon PE Decking Installation Instructions](https://fiberon.widen.net/s/c2schrfsv5/fib_pe_decking--fastener-instructions) — Fiberon. Used for: Residential: 16 in on center perpendicular, 12 in diagonal (up to 45°), 12 in stairs; commercial 12 / 8 / 8 in; ladder-style blocking. Checked 2026-10-06. - [Voluntary Product Standard PS 20-25, American Softwood Lumber Standard: nominal and dressed sizes](https://www.nist.gov/system/files/documents/2024/12/11/PS%2020-25%20Final.pdf) — National Institute of Standards and Technology. Used for: Dry dressed: 1 → 3/4 in; 2 → 1-1/2; 4 → 3-1/2; 6 → 5-1/2; 8 → 7-1/4; 10 → 9-1/4; 12 → 11-1/4. Green: 2 → 1-9/16; 4 → 3-9/16; 6 → 5-5/8; 8 → 7-1/2. Timbers 5–6 in: 1/2 in off. Dry ≤ 19% moisture. Lengths in 1 or 2 ft multiples, trimmed 0 to 3 in over nominal. Checked 2026-10-05. - [Voluntary Product Standard PS 20-25, American Softwood Lumber Standard: definition of board measure](https://www.nist.gov/system/files/documents/2024/12/11/PS%2020-25%20Final.pdf) — National Institute of Standards and Technology. Used for: Board feet = nominal thickness (in) × nominal width (ft) × length (ft). Checked 2026-10-05. **Estimate only.** Results are planning estimates computed from the numbers you enter. They are not engineering, structural, or code advice. Confirm quantities, product yields, and installation requirements with your supplier, the product label, and your local building authority before you order or build.