How to build a deck: permit, footings, framing and boards
Get the design and permit first, then build the footings and posts, the ledger or a freestanding frame, the beams and joists, the decking with its maker’s gaps and fasteners, and last the stairs and railing, with an inspection at each stage your town asks for.
Footing, beam and joist sizes come from an approved plan. The American Wood Council’s free DCA 6 guide gives prescriptive details based on the 2015 IRC; the code your town has adopted decides what applies at your address.
Worked example
Example: a 16 × 12 ft deck, boards along the length, 5.5-inch faces, 1/8-inch gaps, 16 ft boards and 10% extra.
This example gives 29 deck surface boards.
- ceil((12 + 0.010417) ÷ (0.458333 + 0.010417)) = 26
- ceil(26 × 1 × (1 + 10/100)) = 29
Other calculators for this job
Every step of a deck project: measure, the list, what it costs and the quotes.
New deck, new boards or a repair
Replacing only the surface boards is a different job from repairing the frame or building new. Measure the footprint and height from a plan or from the ground, and note stairs, landings, railings and any heavy load such as a hot tub. If only the boards are being replaced, have the frame and ledger checked before the new decking hides them.
Get the design and permit
Under the model code a deck needs a permit unless it is small, low and freestanding: no more than 200 sq ft, no more than 30 inches above the ground at any point and not attached to the house. Your building department says which details it accepts. DCA 6 assumes set materials, spans and loads and leaves out heavy point loads such as hot tubs. Do not size beams, posts or footings by working back from the calculator’s joist spacing.
Attach it to the house, or let it stand alone
A ledger board bolts to the house’s rim joist, with flashing above it to keep water out of the wall. DCA 6 does not allow a ledger on brick or stone veneer or on a cantilevered floor overhang; there the deck stands on its own posts and beam. Tell the installer how your house wall is built and ask how the connection is inspected before it is covered.
Footings, posts, beams and joists
Footings go below the frost line where the ground freezes; the concrete calculator’s post-hole shape gives the bags. Joists usually sit 16 inches apart, and diagonal decking and some composite boards need 12. The deck framing calculator counts joists, beams and posts from your plan; their sizes come from the plan or local code.
Lay the decking
Plan the board direction and lengths so every end joint lands on a joist, and stagger the joints. Leave the gap the decking maker gives and use its fasteners: wood and composite boards differ, and composite brands have their own clips or screws. The deck calculator counts boards and screws from the board width, gap and length.
Stairs, railing and upkeep
A deck more than 30 inches above the ground needs a guard, at least 36 inches high under the model code, with gaps a 4-inch ball cannot pass through. The stair calculator divides the rise into equal steps; stringer size and landing support come from the plan. Keep the inspection sign-offs, product names and care instructions together, and check the deck each spring for loose connections, soft wood and blocked drainage.