DIY & Construction Glossary

Measurement & Estimating

Linear Foot

A measurement of length only — one foot along a straight line, ignoring width and thickness. Lumber trim, fencing, gutters, and countertops are often priced per linear foot, so a 12-foot baseboard is 12 linear feet no matter how tall the board is.

Square Foot vs. Square Yard

A square foot measures area one foot by one foot; a square yard is three feet by three feet, so 9 square feet = 1 square yard. Carpet is traditionally quoted in square yards while most other flooring uses square feet — our carpet calculator converts between the two for you.

Board Foot

The standard volume unit for hardwood lumber: a piece 1 inch thick, 12 inches wide, and 12 inches long (144 cubic inches). Multiply thickness (in) × width (in) × length (ft), then divide by 12 to get board feet.

Cubic Yard

The standard volume unit for concrete, mulch, soil, and gravel: a cube 3 feet on each side, or 27 cubic feet. Ready-mix trucks and bulk landscape materials are sold by the cubic yard — our concrete calculator converts your slab dimensions into yards automatically.

Square (Roofing)

In roofing, a "square" is 100 square feet of roof surface. Shingles are priced and ordered by the square (typically three bundles per square), which is why our roofing calculator reports your roof area in squares.

On-Center (OC) Spacing

The distance from the center of one framing member to the center of the next — not the gap between them. Studs and joists are typically spaced 16" or 24" on-center so that 4-foot-wide sheet goods land on a support at every edge.

Waste Factor

The extra percentage of material you buy beyond the exact measured amount to cover cuts, breakage, mistakes, and pattern matching. Typical waste factors run 5–10% for simple layouts and 15% or more for diagonal installs, complex roofs, or patterned materials.

Coverage Rate

How much area one unit of a product covers — a gallon of paint covers about 350 sq ft, a bag of thinset about 60–70 sq ft. Manufacturers print coverage rates on the label; we've collected the common ones in our material coverage rates reference.

Framing & Structure

Stud

A vertical framing board inside a wall, usually a 2×4 or 2×6 spaced 16" or 24" on-center. Studs carry the wall's weight down to the floor and give you something solid to screw drywall — and heavy shelves — into.

Joist

A horizontal framing board that supports a floor or ceiling, running parallel to its neighbors across the span. Floor joists carry everything above them, which is why their size and spacing are strictly dictated by span tables and code.

Rafter

A sloped framing board that runs from the ridge of a roof down to the exterior walls, supporting the roof deck and shingles. Rafters are cut and installed one at a time on site, unlike factory-built trusses.

Truss

A prefabricated triangular roof frame that combines rafters and ceiling joists into one engineered unit, connected with metal plates. Trusses install fast and span long distances, but you can't cut or drill them without an engineer's sign-off.

Header

A beam that spans the top of a door or window opening and carries the wall's load around the gap. The wider the opening, the deeper the header needs to be — undersized headers are why old doorframes sag.

Top / Bottom Plate

The horizontal boards that cap a framed wall: the bottom plate is nailed to the floor and the top plate (usually doubled) ties the studs together and supports the joists or rafters above. Every stud wall you frame — including a shed wall — starts with plates.

Stringer

The sloped, saw-toothed board that supports a staircase — treads sit on the notches and risers close off the fronts. Most stairs use three stringers, and laying out the notches correctly is the hard part; our deck stair calculator does the rise-and-run math for you.

Ledger Board

The horizontal board bolted to the side of a house that supports one edge of an attached deck. Ledger failures cause most deck collapses, so proper lag bolts or structural screws and flashing here are non-negotiable.

Span

The unsupported distance a joist, beam, or rafter crosses between its supports. Longer spans need deeper or stronger lumber — span tables in the building code tell you exactly what size board can cross what distance.

Load-Bearing

Describes a wall or beam that carries the weight of the structure above it — not just its own weight. Removing or cutting into a load-bearing wall without adding a properly sized beam can crack ceilings or worse, so identify it before demo day.

Frost Line

The depth to which the ground freezes in winter in your area — from a few inches in the South to 4+ feet in northern states. Footings must extend below the frost line so freezing soil can't heave the structure upward.

Footing

The widened concrete base at the bottom of a foundation, post, or pier that spreads the structure's weight over enough soil to keep it from sinking. Footing size and depth are set by local code and the frost line.

Pier

A vertical concrete column (often poured in a cardboard tube form) that supports a post for a deck, shed, or porch. Piers transfer the load down to a footing below the frost line — a common alternative to a full slab foundation.

Concrete & Masonry

Aggregate

The sand, gravel, or crushed stone mixed with cement and water to make concrete — it's most of the volume and gives concrete its strength. "Exposed aggregate" finishes wash away the surface paste to show the stones for decorative effect.

Rebar

Steel reinforcing bar embedded in concrete to give it tensile strength — concrete is strong when squeezed but weak when pulled or bent. Slabs, footings, and walls use rebar (or wire mesh) to control cracking and hold cracked sections together.

Cure vs. Dry

Concrete doesn't harden by drying — it cures through a chemical reaction with water that continues for weeks. It reaches most of its strength in 7 days and its rated strength around 28 days, and keeping it damp early actually makes it stronger.

Slump

A measure of how wet and flowable fresh concrete is, tested by filling a cone with mix and measuring how far it sags when the cone is lifted. Higher slump pours easier but is weaker; adding water on site to make concrete "easier to work" costs you strength.

Mortar

The cement-lime-sand paste that bonds bricks, blocks, and stone together and seals the joints between them. It comes in strength grades (Type N for general use, Type S for structural work) and is softer than concrete by design.

Thinset

A cement-based adhesive troweled in a thin layer to bond tile to floors, walls, and shower pans. "Modified" thinset includes polymers for flexibility and stronger bonding; unmodified is required over some membranes — check both labels.

Deck Mud

A dry, crumbly sand-and-cement mortar (roughly 5:1 sand to cement) packed and screeded to form the sloped base of a tile shower pan. It should just hold a clump when squeezed — our deck mud calculator figures the sand and cement for your pan size.

Grout

The filler packed into the joints between tiles after the thinset cures. Sanded grout is for joints 1/8" and wider, unsanded for narrower joints, and epoxy grout resists stains but is less forgiving to work with.

Control Joint

A groove cut or tooled into a concrete slab that creates a deliberate weak line, so when the slab inevitably shrinks and cracks, it cracks neatly along the joint instead of randomly across the surface.

Mortar Joint

The layer of mortar between bricks or blocks, typically 3/8" thick. Joint thickness affects how many bricks you need per square foot — our brick calculator accounts for it automatically.

Roofing & Exterior

Pitch

The steepness of a roof, expressed as rise over run — a 6/12 pitch rises 6 inches for every 12 inches of horizontal distance. Steeper pitches mean more actual roof surface than the footprint suggests, which is why our roofing calculator asks for it.

Underlayment

The water-resistant layer (felt paper or synthetic sheet) installed over the roof deck before shingles go on. It's the backup defense that sheds any water that gets past the shingles.

Drip Edge

An L-shaped metal strip installed along roof edges that directs runoff away from the fascia and into the gutter instead of wicking back under the shingles. Required by code in most areas and cheap insurance either way.

Flashing

Thin metal (or flexible membrane) installed wherever a roof meets something that interrupts it — chimneys, walls, vents, valleys — to channel water over the joint. Most roof leaks are flashing failures, not shingle failures.

Ridge Cap

The row of specially cut or manufactured shingles that covers the peak of the roof, where the two slopes meet. It sheds water over the ridge line and often covers the ridge vent that lets attic air escape.

Fascia

The vertical board running along the edge of the roof, capping the rafter ends. It's what your gutters attach to, and it's usually the first exterior wood to rot when gutters overflow.

Soffit

The horizontal surface on the underside of the roof overhang, between the fascia and the house wall. Vented soffit panels let fresh air into the attic — a key half of the attic ventilation system.

Gable

The triangular section of wall at the end of a roof with two sloped sides. A "gable roof" is the classic A-shaped roof — the simplest and cheapest style to frame.

Eave

The lower edge of a roof where it overhangs the wall. Eaves keep rain off the siding and windows, and they're where ice dams form in cold climates when attic heat melts snow unevenly.

Sealcoat

A protective liquid coating applied over an asphalt driveway every few years to shield it from sun, water, and chemicals. One 5-gallon pail covers roughly 250–500 sq ft depending on surface condition — size your driveway with our sealcoat calculator.

Lap Siding

Horizontal siding boards installed so each course overlaps the one below it, shedding water like shingles. The overlap means each board covers less than its full width — our siding calculator handles the exposure math.

House Wrap

The synthetic fabric (Tyvek is the famous brand) stapled over wall sheathing before siding goes on. It blocks wind and liquid water from getting into the walls while still letting trapped moisture vapor escape outward.

Interior & Finishing

Drywall Mud / Joint Compound

The spreadable paste used to cover drywall seams, screw heads, and corner bead, sanded smooth between coats. A typical job takes three progressively wider coats — estimate sheets, mud, and tape with our drywall calculator.

Primer

A preparatory coating that seals the surface and gives paint something uniform to grip. You need it over bare drywall, bare wood, stains, and glossy surfaces — skipping it there means more topcoats and worse adhesion.

Cutting In

Painting a clean freehand edge with a brush along corners, ceilings, and trim before rolling the open wall areas. Good cutting in is what separates a crisp paint job from a taped-and-prayed one.

VOC

Volatile organic compounds — the solvents in paints, stains, and adhesives that evaporate as the product dries and cause that "fresh paint" smell. Low- and zero-VOC paints are now standard for interior work and matter for indoor air quality.

Sheen

How shiny a paint finish is, running from flat (no shine, hides flaws, hard to clean) through eggshell and satin to semi-gloss and gloss (durable, wipeable, shows every wall imperfection). Rule of thumb: flatter on ceilings and low-traffic walls, glossier on trim, kitchens, and baths.

Wainscoting

Decorative paneling applied to the lower portion of a wall — typically the bottom 32–42 inches — capped with a rail. Styles include beadboard, raised panel, and board-and-batten; plan the layout with our wainscoting calculator.

Chair Rail

A horizontal trim molding installed around a room at roughly 32–36 inches off the floor — originally to protect walls from chair backs, now mostly to cap wainscoting or visually divide a wall.

Crown Molding

Decorative trim installed at an angle where the wall meets the ceiling, bridging the corner. It's installed "sprung" — leaning between wall and ceiling — which is why its corner cuts are notoriously tricky.

Baseboard

The trim board running along the bottom of a wall where it meets the floor, covering the gap left by flooring and protecting the drywall from vacuum cleaners and feet.

Quarter Round

A small molding shaped like a quarter of a circle, nailed at the bottom of baseboard to cover the expansion gap around the edge of a floor. Its slimmer cousin is called shoe molding.

Miter Cut

An angled cut across the face of a board — most commonly 45 degrees — so two pieces meet in a clean corner, like a picture frame. Outside corners on trim are almost always mitered.

Coping

A trim-carpentry technique for inside corners: instead of mitering both pieces, you cut one piece's end to match the molded profile of the other, so they nest together. Coped joints stay tight when wood shrinks; mitered inside corners open up.

Pattern Repeat

The vertical distance before a wallpaper pattern repeats itself. Larger repeats waste more paper because each strip must be shifted to align the design — our wallpaper calculator factors the repeat into your roll count.

Insulation & HVAC

R-Value

A measure of how well a material resists heat flow — higher R means better insulation. Attics in most of the US should be insulated to R-38 to R-60; see what that means in inches with our attic insulation calculator.

Batt

Insulation manufactured in pre-cut blanket sections sized to fit snugly between studs or joists at standard spacing. Fiberglass batts are the familiar pink or yellow rolls; mineral wool batts are the denser gray-green ones.

Blown-In / Loose-Fill

Insulation (usually cellulose or fiberglass) delivered as loose fluff and blown into place through a hose. It's the fastest way to insulate an open attic and fills irregular spaces batts can't.

Dense-Pack

A technique where loose-fill insulation is blown into closed wall cavities at high density so it can't settle and leave gaps. It's the standard way to retrofit insulation into existing walls without tearing off drywall.

Vapor Barrier

A plastic sheet or coated facing that blocks water vapor from migrating into walls, floors, or crawl spaces where it could condense. Which side of the insulation it belongs on depends on your climate — in cold climates it goes on the warm (interior) side.

BTU

British thermal unit — the energy needed to raise one pound of water one degree Fahrenheit. Heating and cooling equipment is rated in BTUs per hour; find how many your room needs with our BTU calculator.

Tonnage

Air conditioner capacity measured in "tons," where 1 ton = 12,000 BTU per hour of cooling. A typical house needs 2–5 tons; the term comes from the cooling power of melting a ton of ice per day.

SEER2

Seasonal Energy Efficiency Ratio 2 — the current federal efficiency rating for air conditioners and heat pumps, measuring cooling output per unit of electricity over a season. The 2023 minimum is 13.4–14.3 depending on region; higher numbers cost more upfront but less to run.

AFUE

Annual Fuel Utilization Efficiency — the percentage of a furnace's fuel that becomes usable heat. An 80% AFUE furnace sends 20 cents of every fuel dollar up the flue; high-efficiency condensing furnaces reach 90–98%.

Heat Pump

An electric HVAC system that moves heat rather than generating it — pulling warmth from outdoor air in winter and reversing to cool in summer. Modern cold-climate models work well below freezing; see how the economics compare in our heat pump vs. furnace guide.

Mini Split

A ductless heat pump system pairing a small outdoor unit with one or more wall-mounted indoor heads, connected only by refrigerant lines. Ideal for additions, garages, and homes without ductwork — size one with our mini split calculator.

Short Cycling

When a furnace or AC turns on and off in rapid bursts instead of running steady cycles — usually a sign the equipment is oversized for the space. It wastes energy, wears out components, and leaves rooms clammy because the system never runs long enough to dehumidify.

Landscaping

Grade / Grading

The slope of the ground, and the work of reshaping it. Proper grading slopes soil away from the house — about 6 inches of drop over the first 10 feet — so rainwater drains away from the foundation instead of into the basement.

Swale

A shallow, gently sloped ditch — often grassed over and barely visible — that collects surface water and steers it where you want it to go. The low-tech cousin of the French drain.

French Drain

A gravel-filled trench containing a perforated pipe that collects groundwater and carries it away from foundations and soggy spots. Estimate the pipe, gravel, and fabric for your run with our French drain calculator.

Sod vs. Seed

The two ways to start a lawn: sod is farm-grown grass installed as instant carpet-like rolls, while seed is sown and grown in place over weeks. Sod costs 5–10x more but works almost immediately — the full trade-off is in our sod vs. seed comparison.

N-P-K

The three numbers on every fertilizer bag — the percentage by weight of nitrogen (leaf growth), phosphorus (roots), and potassium (overall hardiness). A 24-0-6 bag is 24% nitrogen, 0% phosphorus, 6% potassium; our fertilizer calculator turns those numbers into pounds per 1,000 sq ft.

Overseeding

Spreading grass seed over an existing lawn — without tearing it up — to thicken thin turf and fill bare patches. Best done in early fall for cool-season grasses, right after aerating so seed contacts soil.

Hardscape

The non-living, built parts of a landscape: patios, walkways, retaining walls, fire pits, and driveways. The counterpart to "softscape" — the plants, turf, and soil.

Paver Base

The compacted layer of crushed stone (typically 4–6 inches) under a paver patio or walkway that provides drainage and a stable, frost-resistant foundation, topped with about an inch of bedding sand. Skimping here is why patios heave and wave — get the depths right with our paver calculator.

Surcharge

Any extra weight pushing on the soil behind a retaining wall beyond the soil itself — a driveway, parked car, slope, or building above the wall. Surcharge loads are a key reason taller or loaded walls need engineering and often a permit.

Missing a Term?

If you hit a term in one of our project guides that isn't defined here, it's usually explained in context right where it appears — and every guide links to the calculators that do the math behind it. We add terms to this glossary as new calculators and guides go live.