Window Styles Reference: Double-Hung, Casement, Awning, Slider, and More
Window style — the physical configuration of sashes, frames, and operating hardware — determines ventilation performance, egress compliance, cleaning accessibility, and compatibility with local building codes. This reference covers the principal window types found in US residential and light commercial construction: double-hung, casement, awning, slider, fixed/picture, hopper, jalousie, and specialty forms such as bay and bow. Understanding classification boundaries matters because window style directly affects energy ratings, structural permitting requirements, and long-term replacement cost.
Definition and scope
Window style classification is based on how the glazed sash or panel moves — or whether it moves at all — relative to the fixed frame. The International Residential Code (IRC), published by the International Code Council (ICC), uses this operational distinction as the foundation for ventilation and egress calculations under IRC Section R303 (light and ventilation) and Section R310 (emergency escape and rescue openings).
Operating windows have at least one movable sash. Fixed windows (picture windows) admit no ventilation but maximize glass area and structural continuity. Style also interacts with window frame materials: a vinyl frame is available in nearly every operating style, while aluminum and fiberglass frames dominate commercial slider and curtain-wall applications.
The scope of "window style" stops at the operating geometry. Glazing type, coating, and thermal performance are separate classification systems — covered in resources such as low-e glass coatings and window glass options.
How it works
Each operating style achieves ventilation and weatherproofing through a distinct mechanical path. The breakdown below covers the seven primary styles recognized in residential and light commercial US construction.
-
Double-Hung — Two sashes slide vertically within the frame. Both sashes are operable in a true double-hung; a single-hung has only the lower sash movable. Maximum ventilation area equals roughly 50% of total window area because at least one sash always partially blocks the opening. Tilt-in hardware on both sashes, standard since the late 20th century, allows interior cleaning without ladder access.
-
Casement — A single sash hinged on one vertical side and cranked outward with a gear mechanism. Because the entire sash swings clear of the frame, casements can achieve up to 100% net free area for ventilation. IRC Section R310.2.1 specifies minimum net clear opening dimensions for egress — 5.7 square feet, 24 inches in height, and 20 inches in width — which most full-size casements satisfy.
-
Awning — Hinged at the top, swinging outward at the bottom. The sash acts as a weather canopy, allowing ventilation during light rain. Common in basement and high-wall placements. Net free area is generally 80–90% of rough opening area depending on hardware geometry.
-
Slider (Horizontal Rolling) — Two or more panels in a horizontal track; one or both panels slide laterally. Like single-hung, a standard two-panel slider yields roughly 50% maximum ventilation. Frame depth is shallow, making sliders common in commercial storefronts and manufactured housing where wall depth is limited.
-
Fixed / Picture — No operable sash. Provides maximum glass area, lowest air infiltration, and is structurally simpler than operating styles. Cannot satisfy IRC egress or ventilation requirements on its own but is frequently combined with operating units in mulled assemblies.
-
Hopper — Hinged at the bottom, swinging inward at the top — the inverted configuration of an awning. Most frequently installed in basements; IRC Section R310.2.3 lists minimum dimensions specifically applicable to basement egress windows, requiring a minimum 9 square feet total opening area in many jurisdictions.
-
Jalousie — Multiple horizontal glass slats that rotate simultaneously via a crank. Common in mid-20th century construction, particularly in warm climates. Air infiltration performance is poor by modern standards; the National Fenestration Rating Council (NFRC) air leakage ratings for jalousie units frequently exceed the 0.30 cfm/ft² threshold that ENERGY STAR requires operating windows to meet (ENERGY STAR Windows specification, v7.0, EPA).
Common scenarios
Replacement in existing openings — Full-frame versus insert replacement strategy interacts with style. Double-hung and slider replacements are the most dimensionally forgiving as insert units because the original frame geometry accommodates a new sash assembly within standard tolerances. Casement replacements in older openings sometimes require rough-opening modification when switching from a different operating style.
Egress compliance — Bedrooms on any floor and basements used as sleeping areas require egress-compliant windows under IRC R310. Casements and awnings are the styles most commonly specified for egress upgrades because their full-sash swing can meet the 5.7 square foot net clear opening with a relatively narrow rough opening. Details on sizing, sill height (maximum 44 inches above finished floor), and well requirements are covered in egress window requirements.
Historic structures — Local historic preservation ordinances may restrict the operating style that can replace original windows. Replacement of six-over-six double-hung sash windows in a historic district typically requires approval from the State Historic Preservation Office (SHPO) under Section 106 of the National Historic Preservation Act. Style-compatible replacements — often wood double-hung units — are mandatory in those contexts. See historic home window replacement for jurisdiction-specific framing.
Commercial and multifamily applications — Horizontal sliders and fixed units dominate commercial glazing because they interface cleanly with curtain wall systems and meet AAMA (American Architectural Manufacturers Association) performance grades for wind load and water infiltration. See window replacement in commercial buildings for AAMA 101/I.S.2/A440 classification context.
Decision boundaries
Choosing window style is a constrained optimization across four variables: ventilation need, egress obligation, aesthetic/historic compatibility, and energy performance target.
| Style | Max Ventilation (% of opening) | Egress-capable | Rain-open capable | Typical NFRC Air Leakage |
|---|---|---|---|---|
| Casement | ~100% | Yes | No | ≤0.30 cfm/ft² |
| Awning | ~85% | Limited | Yes | ≤0.30 cfm/ft² |
| Double-Hung | ~50% | Yes (full size) | No | ≤0.30 cfm/ft² |
| Slider | ~50% | Yes (full size) | No | ≤0.30 cfm/ft² |
| Hopper | ~75% | Basement use | No | ≤0.30 cfm/ft² |
| Fixed | 0% | No | N/A | ≤0.10 cfm/ft² |
| Jalousie | ~90% | Rarely | Yes | Often >0.30 cfm/ft² |
NFRC air leakage thresholds cited from NFRC 400 standard.
Egress obligation is binary: if a room is a sleeping area, at least one window must meet IRC R310. This eliminates fixed, hopper (unless basement-specific sizing is met), and jalousie styles from the egress-eligible set in most applications.
Energy performance creates a second filter. Where ENERGY STAR windows are required by local code, energy code (IECC 2021 is adopted in 22 states as of the ICC's adoption tracking), or as a condition of federal tax credits, the jalousie style is effectively disqualified on air leakage grounds alone.
Permitting is triggered when style change accompanies rough-opening modification. A like-for-like replacement — same operating style, same nominal size — typically does not require a permit under IRC Section R105.2 exemptions, though individual jurisdictions vary. Any enlargement or change that affects the structural header, exterior cladding, or egress status requires a permit. Window replacement building permits covers the permit-trigger framework in detail.
Style selection also governs bay and bow window replacement assemblies, which combine fixed center units with flanking casements or double-hungs in a mulled configuration projecting beyond the exterior wall plane — a condition that universally requires structural review and permitting.
References
- International Code Council (ICC) — International Residential Code (IRC), Sections R303, R310
- ENERGY STAR Windows, Doors & Skylights — Version 7.0 Specification (U.S. EPA)
- National Fenestration Rating Council (NFRC) — Standards Overview including NFRC 400
- American Architectural Manufacturers Association (AAMA) — AAMA 101/I.S.2/A440 Fenestration Products Standard
- U.S. Department of Energy — Window Types and Technologies
- National Park Service — Preservation Brief 9: The Repair of Historic Wooden Windows
- [State Historic Preservation Offices (SHPO) Directory —