DIY & Construction Glossary
Plain-English definitions for the construction and DIY terms our calculators use. Each entry links to the calculator that most directly uses it. Bookmark or share individual entries with the anchor link.
Concrete
- 28-day strength
- The compressive strength a concrete mix is designed to reach 28 days after placement, typically 3,000-5,000 PSI. Used as the standard reference point because concrete gains most of its strength in the first 28 days.
- aggregate
- The sand and crushed stone mixed with cement to make concrete. Larger aggregate (3/4") is used in structural concrete; finer (pea gravel or sand) in decorative or topping layers.
- cement vs concrete
- Cement is the binder — a fine powder that reacts with water to harden. Concrete is the full mix: cement + sand + aggregate + water. When someone says "cement driveway" they almost always mean concrete.
- frost line
- The depth in soil where ground temperature stays above freezing year-round. Footings must extend below the frost line to prevent heave damage — 36-48" in northern US, 12-18" in southern.
- monolithic slab
- A slab poured in a single operation with a thickened perimeter that also serves as the foundation footing — common for sheds, garages, and additions in frost-free or well-drained areas.
- slump
- A measure of concrete workability, tested by filling a cone, inverting it, and measuring how far the concrete collapses. Normal slab mix is 4-5"; stiffer (2-3") for footings, wetter (6"+) for pumped walls.
Drywall
- type X drywall
- Fire-rated 5/8" gypsum board with glass fiber reinforcement. Required by code on garage ceilings under habitable rooms, shared walls in multi-family, and specified fire-rated assemblies.
- green board
- Moisture-resistant drywall with a green paper facing. Used on bathroom walls (not showers), laundry rooms, and other humid areas. Not waterproof — use cement board (CBU) in actual wet zones.
- joint compound
- The finishing material used to embed tape over drywall seams and screw dimples. Comes as pre-mixed all-purpose (blue/green lid) or setting-type powder (20/45/90 minute). Rule of thumb: 1 gallon covers ~100 sq ft of drywall across all 3 coats.
- corner bead
- A metal or plastic strip installed on outside (convex) corners to create a straight, durable edge for finishing. Comes in 8, 9, and 10 ft lengths.
Paint
- paint coverage
- Square feet of surface one gallon of paint covers in a single coat. Industry standard is 350 sq ft/gal on smooth interior drywall; drops to 250-280 on textured, 200-250 on exterior siding, and 150-200 on masonry.
- primer
- A preparatory coating applied before finish paint. Required on new drywall, bare wood, over stains, and when changing from dark to light colors. Covers ~300 sq ft/gal. Modern paint-and-primer products can skip separate primer on repaints of similar colors.
- sheen
- The light-reflective quality of a paint finish. Flat/matte hides imperfections (ceilings, low-traffic walls); eggshell and satin add scrub-resistance (living areas); semi-gloss and gloss are most durable and cleanable (trim, doors, baths).
Lumber / Deck
- on-center (OC) spacing
- Distance between the centerlines of two framing members. "16" OC" means joists are centered 16 inches apart. Standard residential deck joist spacing is 16" OC; composite often needs 12" for diagonal lay.
- joist span
- The distance a joist covers between supports. IRC R507.6 publishes maximum deck joist spans by species and spacing — e.g., PT SYP 2x8 @ 16" OC spans 11'10" wet service.
- pressure-treated lumber
- Wood (usually Southern yellow pine) chemically treated under pressure for rot and insect resistance. Standard choice for deck framing and posts. Lifespan: 15-30 years with maintenance. Requires exterior-rated fasteners.
- board foot
- A volume unit for lumber pricing: 144 cubic inches. A 1x12x1 ft = 1 bd ft. A 2x4x8 ft = 5.33 bd ft. Used for pricing hardwoods and bulk lumber purchases.
Landscape / Gravel
- #57 stone
- A 3/4-inch clean crushed stone with no fines (dust). Used as concrete aggregate, driveway top course, and drainage fill. Does not compact.
- #411 / crusher run
- Crushed stone mixed with stone dust and fines. Packs down hard under compaction and is the standard base material under driveways, pavers, and slabs.
- cubic yard
- 27 cubic feet. The standard bulk volume unit for mulch, soil, gravel, and concrete in the US. Covers ~108 sq ft at 3" depth, ~162 sq ft at 2", ~324 sq ft at 1".
- compaction factor
- The ratio of loose volume to compacted volume, typically 1.15-1.30 for driveway base aggregates. Order 15-25% more loose material than the finished compacted volume you need.
- landscape fabric
- A permeable fabric installed under mulch, gravel, or decorative stone to suppress weeds while allowing water through. Non-woven geotextile is the pro choice; woven polypropylene is cheaper and fine for light duty.
Tile
- thinset
- The cement-based adhesive used to bond tile to substrate. Modified thinset adds polymers for flex and bond strength — required for most floor tile. 50 lb bag covers 50-90 sq ft depending on trowel notch size.
- grout
- The filler material between tiles. Sanded grout for joints 1/8" and wider; unsanded for narrower joints on polished stone or glass. Epoxy grout is most durable but harder to work with.
- CBU (cement board)
- Cementitious backer unit — a rigid waterproof substrate (Hardibacker, Durock, Wonderboard) installed under floor and wet-area tile. Replaces plywood or drywall anywhere tile goes in wet or high-moisture zones.
General
- waste factor
- An over-order multiplier to account for cuts, damage, errors, and touch-ups. 10% is standard for simple jobs; 15-20% for complex layouts (diagonal tile, cathedral ceilings, rough subgrades).
- R-value
- A measure of thermal resistance — higher R = better insulation. Fiberglass batt R-13 for 2x4 walls, R-19 for 2x6; blown cellulose R-19 to R-60 for attics. Building code minimums vary by climate zone.
- linear foot vs square foot vs cubic foot
- Linear foot = 12 inches in a single dimension (trim, pipe, lumber length). Square foot = a 12×12" area (tile, flooring, drywall, paint). Cubic foot = a 12×12×12" volume (mulch, gravel, concrete).
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