Free Deck Builder & Materials Estimator
Build your deck from parts: trace your house wall so the deck attaches in the right place, add one or more rectangular sections to make an L, T, or wrap-around shape, then drop in railings and steps wherever you need them. Pick your decking and railing material — the most basic is chosen for you, and pricier options update the cost live. The joists, beams, posts, footings, and decking generate automatically into a framing plan, a section, and a full materials list. Free, no sign-up. This is a planning & estimating aid, not an engineered design or permit set; sizes are conservative DCA 6-based guidance to confirm with your building department.
How to plan a deck that passes inspection
A deck is really two projects: the frame that carries the load and the surface you walk on. Start with the frame. Add a deck section, set its width and depth and how high it sits above the ground, choose attached-to-the-house (a ledger) or freestanding, and the builder sizes the joists, spaces them, drops in a beam and posts, and sizes the footings for you — then lays your decking on top. Not a plain rectangle? Add another section beside it for an L, T, or wrap-around shape; each section is framed on its own. Then add railings and steps as separate pieces you can move, resize, and delete.
The three things inspectors look hardest at are the ledger attachment (the #1 cause of deck collapses — it must be bolted to a solid rim with flashing, never nailed through siding), the footings (below your frost line, sized for your soil), and the guard rail (36 inches high with gaps under 4 inches whenever the deck is more than 30 inches off the ground). The builder flags these, but always confirm the specifics with your local building department.
Standard deck dimensions to design around
Decks are built from standard, buyable lumber and hardware. The builder sizes and counts these for you:
| Element | Standard size | Notes |
|---|---|---|
| Joists | 2×8 / 2×10 / 2×12 PT | Auto-sized to the span; 16" o.c. typical |
| Joist spacing | 16" o.c. (12" for composite/diagonal) | Composite decking needs tighter framing |
| Beam | Built-up 2×10 / 2×12 | Posts about 6–8 ft apart |
| Posts | 6×6 (4×4 for low decks) | On footings below the frost line |
| Footings | 8–16" diameter, ≥ 12" deep | Sized for your soil; below frost |
| Guard rail | 36" high, < 4" gaps | Required when the deck is over 30" up |
| Decking | 5/4×6 PT or composite | Butted with a small gap for drainage |
Frequently asked questions
Is the deck builder really free?
Yes — completely free with no account and no email. Designing the deck, the framing plan, the materials list, the cost estimate, and the CSV/PNG exports are all free.
Can I plan an L-shaped or wrap-around deck?
Yes. Add more than one rectangular section and place them side by side to build L, T, or wrap-around shapes — each section gets its own joists, beam, posts, and footings, and the materials list totals them all together. Railings and steps are separate pieces you add, move, and delete wherever you need them.
How do I attach the deck to my house?
Use “Draw house wall” to trace your house — click each corner of the wall (or the whole footprint) so the plan shows exactly where the house is. Then drag a deck section against a wall and it snaps on as an attached (ledger) deck, with the ledger board and the joist direction set to that wall — so you can even wrap the deck around a corner. The ledger is the #1 deck-failure point, so always confirm the attachment and flashing with your building department.
Which decking and railing material should I pick?
The builder pre-selects the most basic option — pressure-treated decking and a wood railing — so you get a working estimate immediately. Switch decking to composite or the railing to a composite kit or metal balusters and the cost updates live. Each railing can use its own material.
What size joists do I need and how far apart?
It depends on the span (how far the joists reach) and the wood species. The builder auto-suggests a conservative size — for example a 12-foot span often calls for 2×10 joists at 16 inches on-center in Southern pine — but these are prescriptive guidance based on the AWC DCA 6 deck guide; always confirm the size and spacing with your building department, which may adopt a different code.
How are the footings sized, and how much concrete?
Footing diameter comes from the load each post carries and your soil bearing, and the depth must go below your local frost line (which the tool cannot know — you set it). The builder totals the 80-lb bags of concrete for the tube-form footings. Confirm footing size, depth, and frost line with your building department.
Can I use composite decking like Trex?
Yes — pick composite and the builder keeps the framing pressure-treated (composite is a surface only) and tightens the joist spacing to 16 inches, which most composite boards require. Follow your board brand's published span and fastener instructions.
Do I need a permit?
Almost always for an attached deck, and usually for any deck over 30 inches high or above a certain size — plus the ledger, footings, and guard are all inspected items. Check with your local building department before you build, and call 811 before you dig. This tool is a planning aid, not a permit set or engineered design.
Keep planning
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