34 jobsite terms

Construction Glossary

This construction glossary defines the measurements, members, and geometry used across BuildMath tools. Each definition uses plain jobsite language and links to a calculator, chart, or code page where the term affects a numerical result. The complete term list is rendered in HTML and can be read without JavaScript.

Actual dimension: The measured finished size of a dressed lumber member, which is smaller than its nominal trade name.
Baluster: A vertical guard infill member placed between posts or rails.
Birdsmouth: The seat and heel notch that lets a rafter bear on a wall plate.
Board foot: A lumber volume equal to 144 cubic inches.
Bottom chord: The lower horizontal or sloped member of a roof truss.
Clear span: The unsupported distance between the inside faces of bearings.
Common rafter: A rafter running perpendicular from a wall plate to a ridge.
Dead load: The permanent weight of the structure, finishes, and fixed components.
Deflection: The amount a member bends under load.
Gable: The triangular wall end between two sloping roof planes.
Going: The horizontal tread distance used in stair geometry and code checks.
Header: A beam over an opening that transfers load to supporting studs or posts.
Headroom: The vertical clear distance above stairs or walking surfaces.
Hip rafter: The diagonal rafter at the external intersection of two roof planes.
Jack rafter: A shortened rafter that runs between a wall plate and a hip or valley.
Joist: A repeated horizontal framing member supporting a floor, ceiling, or deck.
Landing: A level platform at the top, bottom, or between stair flights.
Live load: Variable load from occupants, movable objects, snow, or use conditions.
Nominal dimension: The trade name used for a lumber size before dressing and finishing.
On center: Spacing measured from the centerline of one repeated member to the next.
Pitch: Roof rise compared with horizontal run, commonly written as rise per 12.
Plumb cut: A vertical cut line on a sloped rafter or stringer.
Rafter: A sloped roof framing member carrying roof sheathing and loads.
Rise: The vertical component of a stair step or roof triangle.
Run: The horizontal component of a stair or roof triangle.
Seat cut: The horizontal bearing cut in a birdsmouth notch.
Slope factor: The multiplier that converts horizontal run or plan area to sloped length or area.
Span: The unsupported distance a structural member crosses between bearings.
Stringer: The inclined stair member supporting treads and risers.
Stud: A repeated vertical wall-framing member.
Tread: The horizontal surface of a stair step.
Valley rafter: The diagonal rafter at the internal intersection of two roof planes.
Waste allowance: Extra material added for cuts, breakage, selection, and field changes.
Winder: A tapered stair tread used to turn a flight without a full landing.