Deck Planning Basics — Size, Layout and Cost
A deck is the most popular DIY project in North America and the most common source of permit problems. Planning decisions made before you buy a single board determine whether the project goes smoothly.
Size it for the house
A deck should be large enough to be useful and small enough that the structure is affordable. The common rule for an attached deck is roughly one square foot of deck per square foot of interior floor area on the adjacent room. A 200 sq ft family room suggests a 200 sq ft deck. Going larger is possible but the framing cost rises faster than the usable area.
Avoid a deck so large it dominates the yard, and avoid one so small people step over it. Under 100 sq ft is rarely worth building; over 400 sq ft crosses into structural design territory in many jurisdictions.
Attached or detached
An attached deck bolts to the house with a ledger board. It is cheaper per square foot, requires a ledger flashing detail, and may need a building permit and engineering depending on height. A detached deck is a standalone structure — simpler to permit but larger, and it is your roof over the door.
Height matters more than size for permit requirements. Most jurisdictions require a permit for any attached deck above a threshold height (commonly 30 inches above grade). Beyond a certain size, a structural engineer's stamp is required — commonly over 500 sq ft or 20 feet high.
Height and footings
Deck height is set by the door threshold. Low decks (under 30 inches) can use simple pads. Taller decks need posts on concrete footings, and those footings must go below the local frost line — 30 to 42 inches in most of the northern US, as little as 15 inches in the south.
Check your frost depth before setting footings. A footing above the frost line will heave, and heaving lifts the whole frame.
Layout decisions to make early
- Where is the door? The deck starts there. Everything else follows.
- How many footings? Feasible spacing is 6 to 10 feet. Closer spacing means more digging but a stiffer frame.
- Railing or not? Railing on any deck over 30 inches above grade is usually code-required. Add it to the material list from the start.
- Stairs or not? A deck 30 inches or higher needs stairs. The run and rise determine the stringers.
- Where does water go? Grade away from the house, and plan for it before the frame goes up.
Material list basics
Beyond decking and joists, a deck needs: a ledger board and flashing, post bases, concrete, joist hangers or blocking at every bearing, structural screws or approved connectors, and a rim board around the perimeter. Post bases are the item most often forgotten, and they are the item that keeps the wood off the ground and out of the splash zone.
Post bases and proper ledger flashing are not optional. They are what prevent the two most common deck failures: wood-to-ground contact rot and ledger rot. Skipping them to save a few dollars costs you the deck in ten years.
Before you build
- Call your building department and ask what a deck permit requires.
- Check your property lines — decks often trigger setback requirements.
- Confirm the frost depth for your area.
- Check whether your homeowners association has rules.
- Verify utility locations before digging any footing.
Recommended for this project
Compare current pricing across major suppliers.
Related tools
WoodCalc is a free independent tool. We may earn a commission when you buy through links on this page. Our recommendations are not influenced by any manufacturer or retailer. See our affiliate disclosure.