Door terminology, plain-English.

Door Anatomy

Slab

The door itself — the panel that swings, slides, or pivots. The "slab" is distinct from the frame and hardware. When someone says "I just need a slab replacement," they mean the moving panel only, leaving the frame in place. For most LA homes we recommend replacing the full pre-hung system rather than just the slab, since old frames usually need updating too.

Pre-hung door

A door slab pre-mounted into a frame at the factory, ready to be installed as a complete unit. The standard configuration for most new door purchases. Includes slab, frame, jambs, threshold (for exterior), and hinge cutouts. Far more reliable than slab-only installation.

Jamb

The vertical and horizontal pieces that make up the door frame. The hinge jamb holds the hinges; the strike jamb has the lock strike plate; the head jamb is the top horizontal piece. Jamb depth must match the wall thickness — common LA residential walls are 4-9/16" or 6-9/16" deep.

Threshold

The bottom piece of an exterior door frame, sealing the gap between the door and the floor. Aluminum thresholds with adjustable inserts last longest in LA. The threshold height affects the floor transition — if the new threshold is taller or shorter than the original, the flooring may need to be trimmed.

Sill

Sometimes used interchangeably with threshold. Technically, the sill is the structural piece beneath an exterior door (often masonry or wood) and the threshold is the finish piece on top of it.

Astragal

The vertical piece that covers the gap between a pair of doors (double doors), or in some single doors, the strip that the lock engages against. For LA double-door entries, the astragal carries the multipoint lock points and weatherstripping that seal the two doors together.

Rail

The horizontal pieces of a paneled door (top rail, lock rail, bottom rail). Less relevant on modern flush slab doors, which don't have visible rails.

Stile

The vertical pieces of a paneled door (hinge stile, lock stile). Like rails, not present on flush slab doors.

Rough opening (RO)

The framed opening in the wall where the door fits. Always larger than the actual door — typically 2 inches larger in width and 2.5 inches larger in height than the door slab. Accurate rough opening measurement is critical for proper door installation.

Handing

Which way a door swings — left-hand or right-hand, inswing or outswing. The single most common ordering error in residential doors. Stand outside the door looking at it: if the hinges are on the left, it's left-hand; on the right, right-hand. Inswing means it opens into the room; outswing means it opens away.

Sidelite

A narrow window-like panel beside a door, typically used to add light to an entry. Standard sidelite widths are 12 or 14 inches. Can be operable (rare) or fixed.

Transom

A window panel above a door — often glass — used to add height and light. Common in homes with 9-foot+ ceilings where the door alone doesn't fill the vertical space.

Door Types

Exterior door

Any door that faces the outside of the home. Engineered differently from interior doors: weatherproof, secure, energy-efficient, and built for daily exposure. See our exterior door collection →

Front door

The primary entry door at the front of the home. The architecturally most prominent door and the highest-impact one for resale value. All front doors are exterior doors, but not all exterior doors are front doors.

Entry door

Any door used as a primary entrance to the home — front, side, or rear. Often used interchangeably with "front door" but technically broader.

Interior door

Any door inside the home, between rooms. Lower engineering requirements than exterior doors (no weather, less security needed) but design quality matters more because they're seen constantly. See our interior door collection →

Pivot door

A door that rotates around a vertical pivot point set into the floor and head jamb, rather than hanging from side-mounted hinges. Allows oversized, heavy doors that hinged systems can't support. Statement entries up to 12+ feet tall and 6+ feet wide are typically pivot doors. Read our pivot door guide →

Flush door

A door with a smooth, uninterrupted surface — no panels, rails, or stiles. Modern doors are predominantly flush. Visually clean and easy to maintain.

Panel door

A door with raised or recessed rectangular panels in the slab — typically 4-panel or 6-panel construction. Traditional aesthetic; less common in modern construction but still right for many traditional and craftsman homes.

Hidden door / jib door

A door designed to blend invisibly into the wall, with a concealed frame and matching wall finish. When closed, it looks like wall. Used for home offices, primary suites, wine rooms, and architectural privacy. See our hidden door collection →

Pocket door

A door that slides into a hollow inside the wall when opened, taking up no floor space when open. Common for small bathrooms, closets, and laundry rooms.

Barn door / sliding door

A door mounted on a track above the opening, sliding sideways rather than swinging. Decorative and space-saving but doesn't seal acoustically or thermally as well as a swinging door.

French doors

A pair of doors with glass panels that meet in the center. Traditional patio/garden door configuration. Modern versions use large single panes or aluminum-and-glass construction.

Dutch door

A door split horizontally so the top and bottom open independently. Niche application — kitchens, nurseries, garages.

Bifold door

A door (or pair) that folds in half when opened. Common for closets and laundry rooms where space is tight.

Materials

Engineered steel

Steel-skinned door slab with internal insulation core and structural reinforcements. Modern engineered steel doors look nothing like the dented utility doors of past decades — premium versions carry stone-effect, wood-grain, or marble finishes. Best ROI for most LA exterior doors.

Fiberglass

Composite door slab made of fiberglass with internal foam insulation core. Modern fiberglass with embossed wood grain looks like real wood at arm's length but doesn't warp, fade, or require refinishing. Strong choice for traditional and Mediterranean LA homes.

Solid wood

A door made from solid wood — usually mahogany, alder, walnut, or white oak. Beautiful but requires more maintenance than steel or fiberglass, especially in LA's sun. Best for shaded entries with committed maintenance.

Solid core

An interior door with a dense wood-fiber or particle core (vs hollow core). Heavier, better acoustically, better-feeling. Standard for any quality interior door.

Hollow core

An interior door with a cardboard honeycomb core. Lightweight, cheap, builder-grade. Sound transmission is high; the door feels insubstantial. Not recommended for any door where quality matters.

Veneer

A thin layer of finish wood (oak, walnut, etc.) bonded to a substrate. Standard construction for premium interior doors — gives you the look of solid wood without the cost or warping risk.

MDF (medium-density fiberboard)

An engineered wood product used as a substrate for veneered doors and as the slab for painted interior doors. Stable, paintable, and consistent. Common in premium painted interior doors.

Thermally broken aluminum

An aluminum door or frame with a polymer or polyamide insert that interrupts heat conduction through the metal. Critical for any aluminum exterior door — without a thermal break, the frame conducts heat freely.

Hardware & Locks

Multipoint lock

A locking system with three or more lock points engaging simultaneously when the door is locked. Pulls the door tight against the frame at multiple positions for security and weather sealing. Standard for premium exterior doors. Read our security guide →

Deadbolt

A single-point lock with a solid bolt that extends from the door into the frame. Standard residential lock. ANSI Grade 1 deadbolts are the security baseline; Grade 2 or Grade 3 are not adequate for primary residence security.

ANSI Grade 1 / 2 / 3

American National Standards Institute rating for residential locks. Grade 1 is highest (commercial-grade durability), Grade 3 is lowest (basic residential). For an LA primary residence, Grade 1 is the right specification — Grade 2 is acceptable but less robust.

Smart lock

An electronic lock with wireless connectivity (Bluetooth, Wi-Fi, Z-Wave, Zigbee). Common features: keypad entry, smartphone unlock, remote unlock, access logs, integration with home security and smart home systems. Standard upgrade for modern LA entry doors.

Lever handle

A horizontal door handle (vs a round knob). Standard in modern construction and required by ADA for accessible openings. Operates more easily than a knob.

Knob

A round door handle. Traditional residential style. Less common in modern construction. Generally not used on exterior doors — levers and bar pulls dominate.

Bar pull

A long vertical or horizontal handle, common on modern entry doors. Often 12-24 inches long. Visual statement piece in addition to functional hardware.

Concealed hinges

Hinges hidden inside the door and jamb when closed. Used on premium interior doors and hidden doors for a clean visual line. Adjustable in 3 dimensions for fine-tuning installation.

Continuous hinge / piano hinge

A hinge that runs the full height of the door rather than separate hinges. Used on commercial doors and some heavy residential applications for stress distribution.

Pivot mechanism

The hardware that allows a pivot door to rotate around its vertical axis. Premium pivot mechanisms have soft-close, hydraulic damping, and adjustability. Critical engineering for any pivot door — cheap pivot mechanisms fail within 1-3 years.

Strike plate

The metal plate on the jamb that the lock bolt engages with. Long strike plates (with extended screw lengths into framing) significantly improve security against kick-in attacks.

Mortise lock

A lock mechanism that fits into a pocket (mortise) cut into the door edge, rather than bored cylindrical holes. More robust and more secure than cylindrical locks. Standard on European multipoint systems.

Glass

Tempered glass

Heat-treated glass that breaks into small dull pieces rather than dangerous shards. Required by California Building Code for any glass in a door or near floor level.

Laminated glass

Two or more glass panels bonded with a plastic interlayer. Stays in place when broken (held together by the interlayer). Required for security glazing and for any glass within 18 inches of a lock.

Low-E glass

Glass with a microscopic metallic coating that reflects infrared (heat) radiation while letting visible light through. Critical for energy efficiency in LA's climate — keeps heat out in summer, in in winter.

Argon-filled glass / argon gas

The space between double-pane glass filled with argon gas instead of air. Argon is denser and slows heat transfer. Standard in premium insulated glass units.

IGU (Insulated Glass Unit)

A multi-pane glass assembly (usually 2 or 3 panes) with sealed gas-filled spaces between. Standard for any exterior door with glass.

Frosted / acid-etched glass

Glass with a translucent, non-transparent finish that lets light through while blocking visibility. Common in modern entry doors for privacy with light.

Fluted glass

Glass with vertical channels or grooves, creating a distorted but partly transparent look. Popular in current modern entry door designs.

Reeded glass

Similar to fluted glass — vertical lines that obscure direct viewing while letting light through. Often used interchangeably with "fluted."

Performance Specifications

U-value / U-factor

A measure of how much heat passes through the door. Lower is better. For LA exterior doors, U-value of 0.30 or lower is the right specification; premium doors achieve 0.20 or lower. NFRC-certified, not just claimed. Read the energy guide →

R-value

The inverse of U-value — measures insulation resistance. Higher R-value means more insulation. Common terminology in walls and insulation; less common (though valid) in doors.

SHGC (Solar Heat Gain Coefficient)

Measures how much solar heat passes through the glass. Lower is better for LA's cooling-dominant climate. For doors with glass facing west or south, SHGC of 0.25 or lower is ideal.

NFRC rating

National Fenestration Rating Council — the independent body that certifies door and window performance ratings (U-value, SHGC, air leakage, visible transmittance). Any claimed performance number should be NFRC-certified, not just manufacturer-claimed.

Title 24

California's energy efficiency code for buildings. Sets minimum performance requirements for doors and windows. All exterior doors sold for installation in California must meet Title 24 requirements for U-value and air leakage. Most premium doors exceed these minimums significantly.

Air leakage rating

Measures how much air passes through the door assembly (slab, frame, seals) under pressure. Lower is better. Standard NFRC air leakage tests use a specific pressure differential. Premium doors achieve air leakage below 0.1 cfm/ft².

STC (Sound Transmission Class)

Measures how well a door blocks airborne sound. Higher is better. Standard residential doors are STC 20-25. Premium solid-core interior doors achieve STC 30-35. Acoustic doors (for studios and home offices) reach STC 40+.

Fire rating

How long a door can resist fire under standard test conditions. Common ratings: 20-minute, 45-minute, 60-minute, 90-minute. Required in California fire zones, between garages and living spaces, and in certain commercial applications. See our Topanga fire-rated door page →

Installation

Weatherstripping

The seal material around the door perimeter that prevents air and water infiltration. Common types: compression (rubber/foam strips), magnetic (refrigerator-style), and bulb (round tube). Magnetic and compression last longest in LA — 20+ years. Friction-fit weatherstripping wears out in 2-3 years.

Door sweep

The strip at the bottom of the door that seals against the threshold. Often adjustable. Critical for air sealing and pest exclusion.

Shimming

The process of using thin tapered wedges (shims) to plumb and square the door frame during installation. The difference between a good and bad install often comes down to proper shimming — the frame must be perfectly true for the door to operate correctly and seal properly.

Plumb

Perfectly vertical. The hinge jamb of a door frame must be plumb for the door to operate correctly. Verified with a level during install.

Square

All corners at exact 90 degrees. The frame must be square for the door to fit properly and the lock to engage. Out-of-square frames are the most common cause of door problems.

Reveal

The visible gap between the door slab and the frame around the perimeter. Should be uniform — typically 1/8 inch — for a properly installed door. Uneven reveals indicate a frame that isn't square or a door that wasn't hung correctly.

Flashing

The water-resistant barrier installed around an exterior door frame to prevent water intrusion into the wall. Critical for any exterior door install — improper flashing causes water damage that may not appear for years.

Caulking / sealant

The flexible sealant used between the door frame and the rough opening to prevent air and water infiltration. Different sealant types for different applications — silicone for high-movement joints, polyurethane for high-bond areas.

Punch list

A final list of small items that need to be completed or corrected at the end of a door install. Standard practice — covers things like adjusting the strike plate, fine-tuning weatherstripping compression, and touching up paint where needed.

Door swing

Which direction the door opens, combined with handing. "Right-hand inswing" means the hinges are on the right (viewed from outside) and the door swings inward when opening.