Construction Terminology: 50+ Essential Terms
Speaking the Language
Every job site has its own shorthand. If you're new to construction, the jargon can be overwhelming. Here are 50+ terms you'll hear on Canadian construction sites, organized by category.
Layout & Measurement
O.C. (On Centre): Spacing measured from the centre of one member to the centre of the next. Standard stud spacing is 16" O.C.
Plumb: Perfectly vertical. Checked with a level or plumb bob.
Level: Perfectly horizontal.
Square: At a 90-degree angle. A framing square or 3-4-5 method verifies square.
Layout: Marking positions for framing members, fixtures, or equipment on the floor, walls, or ceiling.
Chalk line: A string coated in chalk dust snapped against a surface to create a straight reference line.
Dead on: Exactly the right measurement. "That cut is dead on."
Framing
Stud: Vertical framing member in a wall, typically 2×4 or 2×6.
Plate: Horizontal framing member at top (top plate, double plate) or bottom (sole plate) of a wall.
Joist: Horizontal framing member supporting a floor or ceiling.
Header: Beam above a window or door opening that carries the load around it.
Cripple: Short stud above or below an opening.
King stud: Full-length stud beside a window/door opening supporting the header.
Jack stud (trimmer): Shortened stud directly under the header.
Sheathing: Panels (plywood or OSB) covering the framing to add structural rigidity.
Blocking: Short pieces of lumber installed between framing members for support or fire stopping.
Concrete
Formwork: Temporary moulds that hold wet concrete in shape until it cures.
Rebar: Steel reinforcing bars placed inside concrete for tensile strength.
Pour: The act of placing concrete. "We're doing a pour Thursday."
Slump: A measure of concrete workability — how much the cone of concrete settles.
Cure: The chemical process where concrete hardens and gains strength over time (28 days for full strength).
Snap ties: Hardware used to hold concrete forms at the correct spacing.
General Site Terms
Rough-in: First phase of mechanical/electrical installation before walls are closed up.
Trim-out: Final installation of visible fixtures and finish materials.
Punch list: A list of items to fix or complete before a project is considered done.
Change order: A formal modification to the original contract scope or price.
RFI (Request for Information): A formal question to the architect or engineer about plans.
Spec (Specification): Detailed description of materials, methods, or quality standards.
GC (General Contractor): The main contractor responsible for the entire project.
Sub (Subcontractor): A specialized contractor hired by the GC for specific work.
Millwright: A tradesperson who installs, maintains, and repairs industrial machinery.
Tools & Equipment
Skilsaw (circular saw): Handheld power saw for cutting lumber and sheet goods.
Sawzall (reciprocating saw): Power saw for demolition and rough cutting.
Impact driver: Power tool for driving screws quickly — the clicking sound you hear on every site.
Laser level: Projects a level line using a laser beam. Replaced string lines for many tasks.
Transit / Total station: Surveying instruments for establishing points and elevations.
Cat's paw: A small pry bar with a nail-pulling claw on one end.
Safety Terms
Tailgate talk / Toolbox talk: Brief safety meeting at the start of a shift.
LOTO (Lockout/Tagout): Procedure to ensure equipment is de-energized during maintenance.
SDS (Safety Data Sheet): Document detailing hazards of a chemical product (part of WHMIS).
Near miss: An incident that could have caused injury but didn't. Must be reported.
PPE: Personal Protective Equipment — hard hat, boots, glasses, vest, gloves.
JHA (Job Hazard Analysis): Assessment of risks before starting a task.
Keep Learning
The best way to learn construction language is on the job. Don't be afraid to ask what a term means — every veteran was new once. Check the OnSite Pathway for required certifications and training resources.