Wraparound Deck Calculator

Composite L-shape ~408 sqft (24×12 main + 12×10 wing) lands $20,000-30,000 installed nationally; same in PT lands $12,000-18,000; cedar lands $15,000-22,000. U-shape adds 30-40% more (additional wing + second corner). Multiply by 0.92× for South or 1.28× for West Coast labor.

The 90° join where the main deck meets a wing. This corner concentrates stress because it's the structural transition point between two independent framing systems. Reinforcement requires: doubled (sister) joists on both sides of the corner for at least 4 ft, midspan bridging, Simpson hurricane connectors at each joist-to-beam junction, and a corner post bearing on a dedicated 12″ Ø footing. Skipping reinforcement → diagonal sag visible within 5 years.

Aesthetically, mitered transitions (45° at corner) are cleaner and the most common high-end choice — but they add 10-15% waste and 20% labor over straight runs because every miter cut wastes ~4″ of board. Perpendicular rotation runs each segment parallel to its long edge, segments meet at 90° boundary line — lowest waste, simplest install, but visually breaks the deck into two distinct rooms. Picture-frame border is the premium third option that wraps a solid border around the entire perimeter and miters the field boards into it.

Yes — each house wall the deck attaches to gets its own 2×10 PT ledger with through-bolts every 16″ o.c. (per IRC R507.2). For an L-shape attached to a back wall + one side wall, that's 2 ledgers + flashing. For a U-shape attached to back + both sides, that's 3 ledgers. Each ledger needs Z-flashing + spacers behind for water drainage. Improperly flashed ledger is the #1 cause of deck collapse — the 2003 Chicago balcony collapse killed 13 people because of failed ledger attachment.

Possible but challenging. The framing geometry of an inner corner — getting beams to meet at 90° with proper hardware — typically defeats DIY builders. If you DIY, plan: (1) build the main segment first, fully complete framing + hardware, (2) attach wing framing to the main beam at the inner corner with through-bolts, (3) install corner posts on dedicated footings, (4) add sister joists + bridging. Allow 30-50% more time than a rectangle of equivalent total area.

Roughly 1 footing per 8 ft of outboard beam length. A 408 sqft L-shape (24×12 + 12×10) typically has 4-5 main footings + 3-4 wing footings + 1 corner-reinforcement footing = 8-10 total. U-shape adds 3-4 more. Compare to a single 20×20 (400 sqft) rectangle = 6 footings. Wraparound builds use 30-60% more footings.

Almost always — even when single-rectangle decks are exempt in your jurisdiction. Most building departments require structural review for any deck with corners, segments, or non-rectangular footprints because the prescriptive IRC tables assume rectangular framing. Budget $200-400 for permit + inspection. An engineered drawing may be required if total area > 600 sqft or attached to a 2-story house.

Diagonal decking (45° to the long edge) is technically possible on wraparound but adds significant complexity. Each segment runs decking at 45° in its own orientation — at the inner corner, you either (a) miter the diagonal boards to meet at the 90° join (creating a chevron pattern) or (b) install a divider board at the corner separating the two diagonal fields. Option (a) is high-end carpentry; option (b) is more common. Either way, plan for +20-25% waste vs straight diagonal.

U-shape is rare residential — typically requires the house to be a corner lot with no side-yard setbacks. Math: main + 2 wings + 2 inner corners. All the L-shape considerations apply, doubled. Common pattern: 24-ft main along back, 12-ft wings on both sides, totaling ~480 sqft. Project cost lands ~50% above an equivalent rectangle of same total area. Most U-shape builds use perpendicular-rotate corner strategy to keep labor manageable.