Glossary
Thirty deck terms, defined
Every word that turns up on a deck quote, in plain language, and what each part is there to do. Useful for reading a written price line by line rather than nodding along.
- Ledger
- The board bolted to the house that carries one end of the deck joists. It is the single most safety-critical connection on an attached deck, and it must be through-bolted or lag screwed into structure with corrosion resistant flashing over the top. Nailing a ledger to sheathing is the classic cause of a deck separating from a house.
- Rim joist
- The board that runs around the outside edge of a floor frame. On the house it is what a ledger bolts through to. On the deck it is the perimeter board that closes off the joist ends and that guard posts commonly anchor to.
- Joist
- The repeating framing members that span from ledger to beam and carry the decking. Size and spacing are set by span and by the decking material on top, not by habit.
- On center
- How joist spacing is measured and written on a framing plan: center of one board to center of the next, rather than the gap between them. It appears on a quote as "o.c.", and it is the line that tells you how much timber is going into the frame.
- Beam
- The horizontal member carried by the posts that supports the far ends of the joists. Usually two or three plies of dimensional lumber fastened together, sized by span and load.
- Post
- The vertical member carrying the beam down to a footing. On decks that are more than a step or two off the ground, post size and bracing become structural questions rather than cosmetic ones.
- Footing
- The concrete pad or pier under a post that spreads its load into the ground. It has to bear on undisturbed soil and to reach below the depth that freezes, and which of those two governs is found in the open hole rather than predicted from the surface.
- Frost line
- The depth to which ground can be expected to freeze in a given climate. It is a property of the place rather than of the yard, and anything bearing above it moves with the season.
- Frost heave
- The upward movement of soil as water in it freezes and expands. It is why a shallow footing pushes a post up over a winter and why stair stringers should not bear on a slab poured above the frost line.
- Flashing
- The corrosion resistant metal or membrane tucked under the siding and turned out over the ledger, sending water that runs down the wall out over the deck instead of into the joint. The absence of it is discovered during demolition, not before.
- Guard
- The barrier along the open edge of a deck, needed once the surface is high enough that leaving the edge would be a fall rather than a step. Not trim: the posts and their anchors are what make it work, and they are the part nobody looks at.
- Baluster
- The vertical infill members between guard posts and rails. They are spaced closely enough that a small child cannot get through the assembly, which is what sets how many of them a run needs.
- Handrail
- The graspable rail on a stair, and a different object from a guard. It is there to be held on the way down, so it has to be a shape a hand closes around, continuous the length of the flight, and returned into the guard at each end so nothing can hook on it.
- Stringer
- The sawtooth-cut or solid board carrying the stair treads. It bears on a footing rather than on soil or on an existing slab, for the same reason the deck posts do.
- Riser
- The vertical face between two stair treads, and the unit stairs are counted in. Risers on a flight are uniform, because a stair is walked in the dark and the foot expects the next one where the last one was.
- Nosing
- The front edge of a stair tread where it projects past the riser below. The sloped line touching successive nosings is the reference everything else on a flight is set from.
- Landing
- A flat platform at the end of a stair run, or partway down a long one. It gives somewhere to arrive, somewhere to turn, and on a tall flight it breaks the fall distance.
- Pressure treated lumber
- Softwood, usually southern yellow pine, infused with preservative under pressure to resist rot and insects. The default framing material for every deck regardless of what the surface is.
- KDAT
- Kiln dried after treatment. Pressure treated lumber that has been dried following treatment, so it moves less in its first season and accepts a finish sooner than standard wet treated stock.
- ACQ
- Alkaline copper quaternary, one of the common copper based wood preservatives. Its copper content is why aluminum flashing and fasteners should not sit in direct contact with treated lumber.
- Western red cedar
- A naturally rot resistant softwood used as decking and trim. Lighter and more dimensionally stable than treated pine, more pleasant underfoot in summer heat, and it takes a semi-transparent stain evenly.
- Capped composite
- Decking made from a wood flour and polymer core with a hard polymer cap bonded to the exposed faces. The cap is what resists fading, staining, and the surface degradation an uncapped board suffers.
- PVC decking
- Fully synthetic decking with no wood content. Lighter than composite, generally the best performer on heat gain and moisture, and the most expensive per square foot.
- Hidden fastener
- A clip or biscuit system that fixes grooved decking from the side rather than through the face, leaving no screw heads visible. Slower to install and standard on most composite work.
- Picture frame
- A border board running around the perimeter of a deck, with the field boards mitered or butted into it. It hides the cut ends of the field boards and reads as a finished edge.
- Fascia
- The trim board covering the outside face of the rim joist. Usually color matched to the decking, and the detail that separates a finished-looking deck from a framed one.
- Skirting
- Lattice, board, or panel infill closing the gap between the deck edge and the ground. Cosmetic, but it also keeps animals out from under the structure.
- Non-ledger deck
- A deck framed to stand free on its own posts and beams rather than attaching to the house. The standard answer where the wall construction is unknown or cannot be trusted to carry the load, common on older housing.
- Blocking
- Short pieces of timber fitted between the joists to stop them twisting and to give later work something solid to fix into. It is what a guard post anchor reaches for, and it is close to free while the frame is still open.
- Lateral load device
- A tension connector tying the deck frame back into the house floor framing. Standard on attached decks, because it resists the deck being pulled away from the house rather than pushed down.
These terms turn up throughout the build guides. The structural ones are worked through properly in the railing guide and the footings guide.
Thinking about a deck this season?
Call (208) 314-4914 or use the quote form for a free written price on any deck project in the Treasure Valley.