Deck framing calculator

How it is worked out

• Joists are 2×8s, 16 in on centre, between a 2×8 rim round the deck.
• Against a house wall, the side along the wall is a ledger fixed to that wall. The joists hang from it, so the house carries that side.
• A deck 19½ in off the ground or more has dropped beams. Each is two 2×10s under the joists, set in from the edge so the joists run on past it by up to 2 ft, or a sixth of the deck’s depth where that is less.
• A lower deck carries its joists on a doubled rim, in the joists’ own depth.
• Where a joist would span more than 12 ft, another beam is added across the deck.
• Posts are 6×6s at most 8 ft apart under each beam, each on a 16 in square concrete footing a foot into the ground.
• Blocking runs across the joists in lines at most 8 ft apart. Planks are 5/4×6, laid ⅛ in apart and jointed on a joist.

We lay out and count the sizes you pick, close enough to plan a weekend and price the lumber. Span tables, your local code and, on a bigger job, an engineer settle what size each board has to be.

Questions

How far apart are deck joists?

They are set 16 in on centre, the usual spacing under 5/4 decking laid square to the joists.

How many footings does my deck need?

One under each post. Posts stand at most 8 ft apart along each beam, with the end ones about a foot in from the beam’s ends. The list counts them.

Does it include stairs or a railing?

It frames the deck itself. Stairs, guards and the bracing a tall deck needs are yours to add.