Deck glossary

Joist — horizontal framing under the decking. Span is measured face of support to face of support and does not include overhang. Beam — the member the joists bear on, carried by posts. Rim joist — the continuous joist attached across the ends of the other joists; guard posts often attach to it, which is why it must be at least 2x8 nominal.

Ledger board — the framing member fastened to the house that supports the deck's inner edge. Minimum nominal 2x8, must be flashed with approved corrosion-resistant material, and siding must come off before it's installed. Flashing — corrosion-resistant metal of minimum 0.019 inch nominal thickness (or approved non-metallic material) that keeps water out of the ledger connection.

Cantilever / overhang — joist length extending past the beam. Maximum allowable overhang cannot exceed one quarter of the actual main span. Post footing — the concrete pad under a post, bearing on undisturbed soil at least 12 inches below grade or below the frost line, whichever is deeper. Load path — the chain from decking to joist to beam to post to footing to soil; a deck fails at the weakest link in that chain.

Guard — the barrier required where the walking surface is more than 30 inches above grade, minimum 36 inches high, openings no larger than will pass a 4-inch sphere. Baluster — the vertical infill members of a guard. Rise and run — stair geometry; maximum riser 7 3/4 inches, minimum tread 10 inches, with variation between them limited to 3/8 inch. Stringer — the sloped board carrying the treads; must be minimum 2x12, with cut stringers limited to a 6-foot span and solid stringers to 13 feet 3 inches. Hidden fastener — a clip system that secures decking through the board edge instead of the face. Pressure treated — lumber treated with an approved preservative; all field cuts must be treated with an approved preservative such as copper naphthenate.

How to choose

Learn 'ledger' if you learn nothing else

It's the connection to your house, it's the one that fails catastrophically, and it's the one you can't see after the siding goes back.

'Span' has a precise meaning

Face of support to face of support, excluding overhang. Contractors and homeowners often mean different things by it.

'Composite' is a category, not a product

Installed cost ranges $28 to $40 per square foot across very different products. Get the exact product line named in the contract.

Watch for 'per square foot' vs 'installed'

Composite material is $8 to $20 per square foot; installed it's $28 to $40. Those are the same board and very different bills.

'Up to code' is not a specification

Ask for numbers: joist size and spacing, footing depth, guard height. Numbers can be checked.