Deck Glossary

A horizontal dimensional-lumber member running parallel between the ledger and the beam. Carries the decking and transfers load to the beam. Typically 2×8, 2×10, or 2×12 spaced 12-24″ on-center.

A horizontal member running perpendicular to the joists, supported by posts. The load concentrator — every joist's tributary load funnels onto the beam. Almost always doubled or tripled dimensional lumber (2×10 doubled = standard).

A vertical member that transfers beam load to the footing. 4×4, 6×6, or 8×8 PT lumber depending on tributary area + height. Sits in a post-base anchor on top of the footing.

A concrete pier (usually a sonotube) extending below the frost line to provide stable bearing for the post above. Diameter sized to soil bearing capacity + tributary load.

A 2× member bolted to the house rim joist that supports one end of the deck joists. The single most-failure-prone element on residential decks — 90%+ of collapses involve ledger separation.

The outermost joists wrapping the deck perimeter — perpendicular to the field joists at the ends and parallel at the outer edge. Fascia attaches to the rim.

Short pieces of joist lumber installed between joists at mid-span to prevent twisting + improve diaphragm action. Required by IRC R502.7 when joist depth-to-thickness ratio exceeds 6:1.

The area each structural element supports. For a joist between a ledger + a beam: 1/2 the joist span on each side × joist O.C. spacing. Drives sizing for joists, beams, posts, and footings.

A joist that extends beyond its bearing point (beam or ledger). IRC R502.3.3 permits cantilever up to 1/4 of the back-span, max 4 ft.

The chain of structural elements that transfer live load from the deck surface to the soil: decking → joists → beam → posts → footings → soil. Every element must be sized for the same load category.

Southern yellow pine or fir-larch treated with copper-azole or ACQ preservative for ground-contact use. Lowest-cost option, 15-25 year lifespan with biennial sealing.

Western Red Cedar — naturally rot- and insect-resistant. Softer than PT, more dimensional stability, 20-30 year lifespan with biennial sealing. ~50% premium over PT.

Wood-plastic composite (WPC) — recycled wood fiber + polyethylene in a capped polymer skin. Trex, TimberTech, Fiberon. 25-50 year fade-and-stain warranty, no maintenance beyond rinsing.

Solid polyvinyl chloride decking (TimberTech AZEK). No wood content, slightly higher cost than premium composite, best dimensional stability, longest fade warranty (lifetime in some product lines).

Tropical hardwood — densest decking material commercially available. 75+ year lifespan, $90-140/sqft installed. Requires specialty fastening (face-screw + plug, no hidden clips). Sustainability concerns drive most owners to FSC-certified sources.

Tropical hardwood (Brazilian teak) — slightly less dense than IPE, 60-75 year lifespan, ~15-20% cheaper than IPE. Same installation specialty requirements as IPE.

The polymer outer shell on capped-composite boards (covering 3-4 sides). Provides UV + stain + moisture protection. Uncapped composite (10-15 year warranty) vs capped (25-50 year) — always pick capped.

Composite boards come in solid or hollow extrusions. Solid: heavier, stronger, slightly more expensive. Hollow: ~30% cheaper but lower span ratings + can sound hollow underfoot. Most premium lines are solid.

Galvanized steel U-shaped bracket that attaches joists to the ledger or to a beam side. Simpson LUS210, LUS28, LUS210Z are common. Must be nailed per manufacturer spec (10d × 1-1/2″ in EVERY hole).

Heavy-duty wood screw with a hex head, used to attach the ledger to the house rim. 1/2″ diameter at minimum, staggered top and bottom of the ledger, 16″ on-center for standard load.

A composite-specific fastener that attaches the board edge to the joist without penetrating the deck surface. Each board's grooved edge captures the clip; the next board hides the previous one's clip.

Visible screw driven through the board face into the joist. Composite installs sometimes pair with a color-matched composite plug glued into the screw recess to hide the head.

Zinc coating on steel fasteners to resist corrosion. Hot-dip galvanized (HDG) is the standard for PT lumber; G185 is the minimum for ACQ-treated PT (ACQ accelerates corrosion of lesser-galvanized steel).

Metal bracket bolted into the top of a footing, holding the post off the concrete. Lifts wood 1″ above concrete to prevent rot. Simpson ABU44Z, ABU66Z are common.

Specialty connector that resists uplift force (typically used in hurricane zones + seismic zones). Connects joists to beams or beams to posts. Simpson H1, H2.5, H8 are common.

International Residential Code — the model residential building code published by ICC every 3 years. IRC 2021 is the current edition and includes deck-specific section R507 for the first time. Most jurisdictions adopt with a 3-6 year lag.

International Code Council — non-profit that develops and publishes the IRC, IBC (commercial), IFC (fire), and related model codes. Your AHJ adopts ICC codes and may modify them.

Authority Having Jurisdiction — the local building department, permit office, or municipality that enforces the code in your specific location. AHJ rules supersede national IRC defaults.

Maximum allowable mid-span deflection: span (in inches) divided by 360. For an 8 ft (96″) span: 96/360 = 0.267″ max sag. IRC R502.3.2 requires L/360 for residential.

Variable weight added to the structure by occupants, furniture, snow, etc. IRC R301.5 minimum is 40 psf for residential decks. Snow + concentrated loads (hot tub, BBQ island) get additional design considerations.

The structure's own weight — lumber, fasteners, decking, railing. Typically 10-15 psf for a residential deck. Constant by definition, never removed.

The depth to which soil freezes in winter. Footings must extend below this depth + 6″ into stable bearing soil per IRC R403.1.4 to prevent frost-heave damage. Varies 12-48″ across the US.

Guardrail balusters + cable runs must be spaced so a 4″-diameter sphere cannot pass through. Prevents children from getting limbs trapped. Most builders space at 3-3/4″ for safety margin.

36″ minimum for residential decks over 30″ above grade. Commercial + multi-family is 42″. Measured from the deck top to the top of the rail.

Max riser height 7-3/4″, min tread depth 10″ (IRC R311.7.5). All risers within a flight must vary by ≤ 3/8″. The rise-run pair determines stair angle (typically 30-37°).

A perimeter band of contrasting decking wrapping the deck edge. Hides board ends, creates visual framing, adds ~$4-7/lf cost premium. Pairs especially well with two-tone composite product lines.

Layout direction of the deck boards: straight (parallel), diagonal (45°), herringbone, chevron, picture-frame. Pattern affects waste factor (7-28%) and joist O.C. requirements (12-24″).

The 3/16″ space between adjacent deck boards. Allows thermal expansion + drainage. IRC R507.6 specifies 1/8″ minimum; 3/16″ is standard for capped composite.

Closed risers fill the vertical face between treads (a board behind each riser). Open risers leave the face exposed. IRC R311.7.5.1 limits open-riser openings to 4″ sphere clearance — typically requires closed risers in residential.

Decorative board covering the rim joist face. Hides the structural lumber and gives the deck edge a finished look. Typically PT cedar or composite that matches the decking.

Decorative lattice or solid board panels covering the open space below the deck (between deck and ground). Cosmetic + keeps animals out + provides ventilation.

Vertical pickets between guardrail top + bottom rails. Typically 2×2 wood, 3/4″ square aluminum, or 1/2″ stainless cable. Spaced per 4-inch sphere rule.

Larger post at the start, end, and corners of a stair flight or guardrail run. Anchors the rail system + handrail. Typically 4×4 or 6×6 PT or composite-wrapped.

Written authorization from the AHJ to build. Required for almost all decks attached to a house and most freestanding decks over 30″ height or 200 sqft. Fees $80-$450 typical.

AHJ field visit to verify built work matches the permit drawings. Typically 2-3 inspections per deck: footings before pour, framing before decking, final after railing.

Minimum distance the deck must sit from property lines, easements, or septic systems. Determined by zoning code, not building code. Often 5-10 ft from side lines, 10-25 ft from rear.

A legal right for another party (utility company, neighbor, municipality) to use part of your property. Decks cannot be built over easements without recorded permission.

Deck design certified by a licensed professional engineer (P.E.). Required by most AHJs for: multi-level decks, hot tub installs, cantilevers > 4 ft, hillside footings, decks over 12 ft above grade.

Itemized count of lumber, fasteners, hardware, and decking needed to complete the build. Generated by deck cost calculators + adjusted for waste factor + sales tax + delivery.

The percentage of material lost to cuts, defects, and re-cuts during install. 7% straight pattern, 14% diagonal, 22% octagonal, 28% curved. Order this much extra beyond the install quantity.

Per-element load math: the area of deck surface each joist, beam, or post supports. Drives sizing for that element. Tributary = half joist span × O.C. spacing for joists.