Construction wiki
Construction Glossary
Plain-English definitions with the formulas, code references and calculators behind them.
A
- AggregateConcrete
- Aggregate is the sand, gravel or crushed stone that makes up 60–75% of concrete's volume. US sizes, ASTM C33 grading and how aggregate is sold.
B
- Birdsmouth CutFraming
- A birdsmouth is the triangular notch that lets a rafter sit flat on the wall's top plate. Seat cut, heel cut, IRC bearing and how deep you can cut.
- Board Foot (BF)Lumber
- A board foot is 144 cubic inches of lumber — 12" × 12" × 1" nominal. How US lumber yards calculate, price and quote board feet, with worked examples.
C
- Clear SpanFraming
- Clear span is the open distance between the inside faces of supports. How it differs from building span and rafter run, and how IRC span tables use it.
- Concrete FootingConcrete
- A footing is the widened concrete base that spreads a wall's or post's load into the soil. IRC minimum size, frost depth, rebar and how to estimate the concrete.
- Cubic Yard (yd³)General
- A cubic yard is 3 ft × 3 ft × 3 ft = 27 cubic feet — the US unit for ordering concrete, gravel, mulch and soil. Formulas, coverage and conversions.
D
- Drywall Joint Compound (Mud)General
- Joint compound ("mud") fills and hides drywall seams and screws. Ready-mix vs. setting-type, the three-coat process, and how much to buy per 1,000 sq ft.
E
- EaveRoofing
- The eave is the lower edge of a roof that overhangs the wall. Overhang widths, soffit venting, drip edge and ice barrier requirements under the IRC.
F
- Fascia BoardRoofing
- Fascia is the trim board fastened to the rafter tails along the eave. Sub-fascia vs. finish fascia, common sizes and materials, and how gutters and drip edge attach.
- Floor and Ceiling JoistFraming
- Joists are the horizontal framing members that support floors and ceilings. Typical sizes and spacing, IRC span tables, deflection limits, and notching rules.
- Framing HeaderFraming
- A header is the beam over a door or window opening that carries the load around it. Built-up 2x headers, IRC span tables, jack and king studs, and nonbearing walls.
K
- King StudFraming
- A king stud is the full-height stud on each side of a door or window opening. How king, jack and cripple studs work together, and how they add to a stud count.
L
- Live Load vs. Dead LoadGeneral
- Dead load is the permanent weight of the building; live load is people, furniture and stored items. IRC design values in psf and how they size joists and rafters.
N
- Nominal vs. Actual Lumber SizeLumber
- A 2x4 is really 1-1/2" × 3-1/2". Why nominal lumber sizes differ from actual dressed sizes under PS 20, the subtraction rule, and when it matters.
O
- On Center (OC) SpacingFraming
- On center (OC) is the distance from the center of one framing member to the center of the next — 16" OC and 24" OC are the US standards. How to lay it out.
P
- Plumb vs. LevelGeneral
- Plumb means perfectly vertical; level means perfectly horizontal. How carpenters check plumb and level, the tools used, and why "square" is the third rule.
- Portland CementConcrete
- Portland cement is the gray powder that binds sand and gravel into concrete. ASTM C150 types, the cement vs. concrete difference, water-cement ratio and curing.
R
- Rebar & Wire MeshConcrete
- Rebar is ribbed steel bar that gives concrete tensile strength. US bar sizes (#3,
- Roof PitchRoofing
- Roof pitch is the vertical rise of a roof in inches for every 12 inches of horizontal run, written as 6/12 or 6:12. How to measure it, convert it to degrees and use it.
S
- Stair Stringer Rise and RunStairs
- Total rise, total run, unit rise (riser) and unit run (tread) on a stair stringer — definitions, IRC limits, the 2R + T comfort rule and how to lay out a stringer.
- Stair Tread and RiserFraming
- The tread is the horizontal surface you step on; the riser is the vertical face between steps. IRC limits, nosing, open risers and common tread materials.
T
- Top Plate and Bottom PlateFraming
- Wall plates are the horizontal members at the top and bottom of a stud wall. Double top plates, 24" joint offset, treated sill plates and anchor bolts under the IRC.
V
- Vapor Barrier / Vapor RetarderGeneral
- A vapor retarder slows moisture moving through walls, floors and slabs. IRC Class I, II and III ratings, 6-mil poly under slabs, and where it goes by climate zone.