Deck Project Planner

Three orders, one set of dimensions

A deck gets ordered in stages, and the stages have to match. The frame decides where the boards land. The board direction decides the joist spacing. The square footage decides the stain. Get the frame wrong and everything downstream is wrong with it.

Width and depth go in once. The joist count, hanger count and board count all come off them.

Sketch the frame before you count anything

The printed sheet has a grid for this and it is the most useful part of the page. Draw the ledger, the beam line, the post positions and the joist direction. Ten minutes here finds the problems — a post landing where a downpipe is, a beam that needs to be two spans rather than one, stairs coming off the wrong side.

Span is the number that matters

Joist size is not a preference. A 2 × 8 in southern pine spans 11 ft 10 in. at 16 in. centers; in hem-fir it is 10 ft 11 in. Go past it and the deck is bouncy at best. The deck framing calculator checks your depth against the code table and tells you whether the joist you picked reaches.

Work that out before you sketch anything, because it decides whether you need a beam part-way out.

Board direction changes the frame

Boards laid diagonally cross the joists at 45 degrees, so each board effectively spans about forty per cent further. That is why diagonal decking wants joists at 12 in. centers rather than 16 — a decking requirement, not a structural one, and one that adds a third more joists to the order.

Most composite boards specify 12 in. centers too. Check the decking manufacturer's instructions before you fix the frame spacing, not after.

The finish is part of the order

Stain is easy to leave until the end and then under-buy, because the railing is usually more surface than the deck itself. Forty feet of spindle railing is around 480 sq ft of actual surface against 320 sq ft of boards. The deck stain calculator works it out properly.