Siding and Window Glossary

Siding and window quotes are full of words most people never need until they are comparing bids. Here they are in plain language, each linked to the guide that explains it in full.

A

Allowance

An amount set aside in a contract for an item that cannot be priced exactly when the contract is signed, such as rot repair or a finish still to be chosen. The contract should say how the actual cost is reconciled against it. Read more

Argon gas fill

An inert gas sealed between the panes of an insulated window. It conducts heat less readily than air, which improves the window’s insulating value. Read more

Awning window

A window hinged at the top that opens outward from the bottom, so it can stay open for ventilation in light rain. Read more

B

Board and batten

A vertical siding style: wide boards or panels with narrow strips (battens) covering the joints between them. Read more

C

Casement window

A window hinged on one side that swings outward like a door, usually operated with a crank. Read more

Caulk

A flexible sealant used at joints and around windows, doors and trim. It is a maintenance item; it does not replace flashing as the primary defence against water. Read more

Chalking

A powdery residue on a painted or factory-finished surface, caused by the finish breaking down in sunlight. Read more

Change order

A written amendment to a signed contract that changes its scope, price or schedule. Read more

Climate zone

One of the 16 zones California’s Energy Code uses to set efficiency requirements. Which zone you are in decides the window performance your project must meet. Read more

Condensation between the panes

Fog or moisture sealed inside a double- or triple-pane window. It means the seal of the insulated glass unit has failed, and it cannot be wiped away. Read more

Contingency

Money held back from a project budget to cover what cannot be known in advance, most often damage found once the old siding comes off. Read more

CSLB

The Contractors State License Board, the California agency that licenses contractors. Its website lets anyone check whether a license is active. Read more

D

Defensible space

The area around a building where vegetation and other fuel are managed to slow a wildfire. California law requires 100 feet of it in state responsibility areas and in Very High Fire Hazard Severity Zones. Read more

Double-hung window

A window with two sashes that both slide up and down. On a single-hung window, only the lower sash moves. Read more

Dry rot

Decay of wood caused by fungi. Despite the name, it needs moisture to start; the wood becomes brittle and crumbles. Read more

E

Efflorescence

A white, crusty deposit left on masonry, stucco or cement-based siding when water carries salts to the surface and evaporates. It is a sign of moisture moving through the material. Read more

Egress window

A window large enough, and low enough from the floor, to serve as an emergency exit from a sleeping room. Read more

Ember-resistant vent

A vent designed to keep burning embers and flames out of an attic or crawlspace. In California fire hazard zones, new construction must use vents listed by the State Fire Marshal or tested to ASTM E2886. Read more

ENERGY STAR

The U.S. EPA’s efficiency label. For windows, the criteria vary by climate region. Read more

Engineered wood siding

Siding made from wood strands or fibers bonded with resins and treated against moisture and insects. LP SmartSide is a common brand. Read more

Exposure (reveal)

The visible width of each course of lap siding once it is installed, which is less than the full board width because of the overlap. Read more

F

Fascia

The vertical board along the edge of the roof, below the roof edge. Gutters are usually mounted on it.

Fiber cement siding

Siding made from cement, sand and cellulose fibers. It resists rot, insects and fire, and is sold as planks, panels and shingles. James Hardie is the best-known brand. Read more

Fire Hazard Severity Zone

An area mapped as Moderate, High or Very High fire hazard under California law. Whether a property is in one decides whether the state’s wildfire construction rules apply. Read more

Flashing

Thin metal or membrane pieces installed at joints, openings and roof-wall intersections to direct water out of the wall. Kickout and Z-flashing are common types on siding jobs. Read more

Full-frame replacement

Removing an old window down to the rough opening, including its frame, and installing a new window with its own frame. Also called new-construction replacement. Read more

H

Hardboard siding

Siding made from compressed wood fibers, sold under names such as Masonite. Many older installations have failed through swelling and delamination. Read more

HardiePanel

James Hardie’s large-format vertical fiber cement sheet, often used with battens for a board-and-batten look. Read more

HardiePlank

James Hardie’s horizontal lap siding board. Read more

HardieShingle

James Hardie’s fiber cement siding made to look like cedar shingles. Read more

HardieZone

James Hardie’s system of climate-specific product lines, formulated for either freeze-thaw or warmer climates. Read more

Housewrap (weather-resistive barrier)

A sheet material installed over the sheathing, behind the siding. It sheds any water that gets past the siding while letting water vapor escape. Read more

I

Ignition-resistant material

A building material that has passed the fire and weathering tests California’s Wildland-Urban Interface Code sets for resisting ignition. Noncombustible materials also count as ignition-resistant. Read more

Insulated glass unit (IGU)

Two or more panes of glass sealed together around the edges with a gap between them. Dual-pane and triple-pane windows use IGUs. Read more

Insulated vinyl siding

Vinyl siding with a rigid foam backing bonded to it, adding a little insulation and stiffening the panel. Read more

L

Laminated glass

Two layers of glass bonded to a plastic interlayer that holds the pieces together if it breaks. It also reduces noise. Read more

Lap siding

Horizontal siding in which each board overlaps the one below it. Read more

Low-E coating

A microscopically thin metallic coating on window glass that reflects heat, keeping heat in during winter and out during summer. Read more

N

NFRC label

The sticker on a new window with its tested performance ratings: U-factor, solar heat gain coefficient, visible transmittance and, optionally, air leakage and condensation resistance. Read more

Noncombustible

In building codes, a material that passes the ASTM E136 fire test, meaning it does not ignite or add fuel to a fire. James Hardie fiber cement siding has been tested to it. Read more

O

Obscure glass

Patterned or frosted glass that lets light through while blocking a clear view. It is used in bathrooms and entries. Read more

R

Retrofit window

A replacement window installed into the existing window frame, leaving the surrounding siding or stucco largely undisturbed. Read more

S

Sash

The part of a window that holds the glass, together with its frame members. On an operable window, it is the part that moves. Read more

Sheathing

The structural panels, usually plywood or OSB, nailed to the wall framing. The weather barrier and siding are installed over it. Read more

SHGC (solar heat gain coefficient)

The fraction of the sun’s heat that passes through a window, from 0 to 1. Lower means less heat gain, which matters most in hot climates. Read more

Sliding window

A window whose sash slides sideways along a track. Read more

Soffit

The underside of the roof overhang, between the wall and the fascia. It is often vented.

Square

The unit roofers and siding installers price and order by: one square is 100 square feet of wall or roof coverage. Read more

STC (sound transmission class)

A rating of how well a wall or window blocks airborne sound. A higher number means better noise reduction. Read more

Stucco

A cement-based plaster applied over lath to form a hard exterior wall finish. Read more

T

T1-11

Grooved plywood siding panels, common on older and budget homes. Read more

Tempered glass

Glass heat-treated so that it breaks into small, blunt pieces instead of sharp shards. Building codes require it in certain locations near doors, floors and bathtubs. Read more

Title 24

Title 24 of the California Code of Regulations: the state’s building standards. Its Part 6, the Energy Code, sets the efficiency requirements for replacement windows. Read more

Trim

The boards around windows, doors, corners and the base and top of walls that finish the edges of the siding. Read more

U

U-factor

How readily a window conducts heat. The lower the number, the better the window insulates. California’s Energy Code sets a maximum for replacement windows. Read more

V

Vinyl siding

Siding made from PVC. It is lightweight and low-cost, and it never needs painting. Read more

Visible transmittance (VT)

The fraction of visible light a window lets through, from 0 to 1. A higher number means more daylight. Read more

W

Weep screed

The perforated metal strip at the base of a stucco wall that lets water drain out and sets the clearance to the ground. Read more

Wildland-Urban Interface Code

Title 24, Part 7 of California’s building standards, which has governed construction in wildfire hazard areas since 1 January 2026. It replaced Chapter 7A of the California Building Code. Read more

Z

Zone 0

The 5 feet immediately around a house, where Board of Forestry regulations adopted in August 2026 will limit plants, mulch and other combustible material. As of September 2026 they were not yet in effect. Read more

Definitions are general. Code requirements, product specifications and warranty terms are set by the relevant code or manufacturer; the linked guides cite them.