Construction Glossary: 100 Terms Every DIYer Should Know
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Concrete & Masonry
Admixture
Any material added to concrete other than water, cement, and aggregate. Includes plasticizers, air-entraining agents, accelerators, and retarders.
Air entrainment
Intentionally mixing tiny air bubbles into concrete to improve freeze-thaw durability. Required in cold climates (5–7% air).
Bleed water
Water that rises to the surface of fresh concrete as heavier particles settle. Do not add water to replace it — wait for it to evaporate before finishing.
Cold joint
A plane of weakness formed when fresh concrete is placed against concrete that has already begun to set. Avoidable by continuous pouring.
Control joint
A planned groove cut or formed into a slab to concentrate cracking in a straight line rather than letting it wander. Spaced at 8–10× slab thickness.
Curing
Maintaining adequate moisture and temperature in fresh concrete for 7–28 days to ensure complete cement hydration and full strength development.
Expansion joint
A full-depth separation between concrete sections that allows independent movement without cracking. Required at all fixed abutments.
Fly ash
Byproduct of coal combustion used as a partial cement replacement. Improves workability and long-term strength; reduces heat of hydration.
Footing
The below-grade widened base of a foundation or column that transfers structural loads into the soil. Must extend below frost line.
Frost line
The depth to which soil freezes in winter. Footings and posts must be below this depth to prevent frost heave. Ranges from 0 in (south Florida) to 60+ in (Minnesota).
Grout
A thin mortar used to fill joints in tile and masonry, and to fill spaces under posts and columns.
Mortar
A cement + sand + water mix (no aggregate) used for masonry joints, tile bedding, and stucco. Not the same as concrete.
PSI
Pounds per square inch — the compressive strength of concrete at 28 days. Most residential work specifies 3,000–4,000 PSI.
Rebar
Deformed steel reinforcing bar embedded in concrete to resist tensile forces. Common sizes: #3 (3/8 in), #4 (1/2 in), #5 (5/8 in).
Slump
A measure of concrete workability. A 4-in slump is typical for slabs. Higher slump = more water = lower strength.
Spalling
Flaking or chipping of the concrete surface, usually caused by freeze-thaw cycling in low-quality or improperly cured concrete.
W/C ratio
Water-to-cement ratio by weight. The single most important factor in concrete strength. Lower is stronger (0.35–0.50 is the residential range).
WWF
Welded wire fabric — a grid of steel wires used as slab reinforcement. Common spec: 6×6 W1.4/W1.4 for residential slabs.
Framing & Structure
Board foot
Unit of lumber volume: 1 ft × 1 ft × 1 in (144 cubic inches). Used to price dimensional lumber.
Bearing wall
A wall that carries structural loads from above down to the foundation. Cannot be removed without temporary shoring and structural replacement.
Blocking
Short pieces of lumber installed between studs, joists, or rafters for fire stopping, lateral bracing, or to provide nailing surface.
Cantilever
A structural member that extends beyond its support without a post at the end. Decks often cantilever 2 ft beyond the beam.
Header
A horizontal structural member spanning a door or window opening to carry the load of the wall above.
Joist
Horizontal structural member supporting a floor or ceiling. Sized by depth (2×8, 2×10, 2×12) — deeper = longer span possible.
King stud
Full-height stud on either side of a door or window opening. The header rests on trimmer studs attached to the king studs.
Ledger
A horizontal structural member bolted to the house to support one end of deck joists. The most critical connection on a deck — ledger failures cause collapses.
Live load
Temporary or moving load: people, furniture, snow. Residential decks designed for 40 psf (pounds per square foot) live load.
LVL
Laminated veneer lumber — engineered structural beam made from thin wood layers glued with the grain parallel. Stronger and straighter than sawn lumber.
Nominal vs. actual
Lumber sizes are sold by nominal name but are smaller when dried and planed. A "2×4" is actually 1.5 in × 3.5 in.
On-center (O.C.)
Measurement from the center of one framing member to the center of the next. Standard stud spacing is 16 in O.C.
Rim joist
The outer joist that frames the perimeter of a floor or deck, to which other joists attach.
Sheathing
Panel material (plywood, OSB) nailed to studs or rafters to provide a nailing base for cladding and to resist racking forces.
Span
The unsupported horizontal distance a beam or joist must bridge. Span tables in code books give allowable spans by lumber species, size, and spacing.
Stud
Vertical framing member in a wall. Standard spacing is 16 in O.C. for most residential walls; 24 in O.C. for some energy-efficient framing.
Roofing
Bundle
A package of asphalt shingles. Standard architectural shingles come 3 bundles per square (100 sq ft).
Dead valley
A low-slope roof section that drains slowly. Requires extra waterproofing (I&W shield).
Drip edge
Metal flashing installed at the eaves and rakes to direct water off the fascia and into the gutter.
Eave
The lower edge of a roof that overhangs the wall below.
Felt / underlayment
Water-resistant layer installed over the deck and under shingles. 15-lb and 30-lb felt are common; synthetic underlayment has replaced felt in many applications.
Flashing
Metal pieces installed at roof penetrations and intersections to prevent water entry. Includes step, counter, base, and cap flashing.
Hip
A roof design with slopes on all four sides meeting at a ridge. More wind-resistant than a gable roof.
Ice & water shield (I&W)
Self-adhering waterproofing membrane applied at eaves, valleys, and penetrations. Required by code in most cold climates.
Pitch
Roof slope expressed as rise-over-run: "4/12" means 4 in of rise per 12 in of horizontal run. Affects shingle selection, safety, and material quantities.
Rake
The sloped edge of a gable roof, running from eave to ridge.
Ridge
The highest horizontal line of a roof, where two sloping surfaces meet.
Square
Roofing unit equal to 100 sq ft of roof surface. A 2,000 sq ft house with a 5/12 pitch roof is approximately 24 squares.
Valley
The internal angle where two roof slopes meet, forming a channel for water runoff.
Paint & Finishes
Coverage rate
How much surface area one gallon of paint will cover. Manufacturers typically state 350–400 sq ft/gallon on bare surfaces; expect 300–350 on textured walls.
Cut-in
Painting a precise edge along corners, trim, or ceilings using a brush before rolling the field.
MIL
Unit of paint film thickness (1 mil = 0.001 inch). Wet mil vs. dry mil differ because solvent evaporates during cure.
Primer
First coat applied to a bare or repaired surface to seal, promote adhesion, and block stains. Never skip primer on new drywall.
Sheen
The glossiness level of paint: matte/flat, eggshell, satin, semi-gloss, high-gloss. Higher sheen = more washable but shows surface imperfections more.
VOC
Volatile organic compounds — chemicals that off-gas from paint. Low-VOC (<50 g/L) and zero-VOC paints are safer for indoor air quality.