Casement Windows

Summary

Casement windows are sashes hinged on one side that swing outward on friction hinges or operators, sealing against compression weatherstripping when closed; tilt-turn variants swing inward. They give full-opening ventilation, easy egress, and tight seals, but sash width, swing clearance outside, and screen location must be coordinated.

Cols

Image

Casement Windows.png

Operator: crank or lever mechanism that opens the sash; folding handles avoid conflicts with blinds
Push-out casement: opened by handle and push, without a crank
Friction hinge / four-bar hinge: hinges that hold the sash at any opening and shift it away from the frame for cleaning
Egress hinge: hinge that lets the sash open to about 90 degrees for full clear opening
Multipoint lock: locking points along the lock stile that pull the sash tight to the seal
Compression seal: weatherstrip compressed by the closed sash; tighter than sliding seals
Tilt-turn: inswing European sash that tilts in from the bottom for ventilation or swings in fully
Handing: hinge side, viewed from the exterior
Interior screen: screen on the inside face, since the sash swings out
French casement: pair of sashes with no center post, opening outward from the middle
Window opening control device (WOCD): limiter that restricts opening for fall protection and releases for full opening

Standards

Sizes

Sash width limited by hinge and operator capacity; tall narrow units common
Wider openings made by mulling multiple casements or pairing with fixed units
Egress sizing: the net clear opening depends on sash width, hinge type, and opening angle; check the manufacturer's clear opening data

Ratings

NAFS performance class: R and LC common in residential; CW and AW available in heavier commercial lines
Air leakage: among the tightest operable types; wind pressure presses the sash against its seal
Water: outswing sash sheds water well; inswing tilt-turn depends on sill design

Test standards

AAMA/WDMA/CSA 101/I.S.2/A440 (NAFS-22): performance, operating force, and labeling
ASTM E283, E331, E330: air, water, and structural
ASTM F2090: window opening control and fall prevention devices
NFRC 100, 200, and 400: U-factor, SHGC, and air leakage

Materials

Vinyl: residential; limits on sash size and dark colors
Fiberglass: stiff frames for larger sashes and dark finishes
Clad wood: interior wood with aluminum or fiberglass exterior cladding
Aluminum, thermally broken: commercial project-out and casement vents
Hardware: stainless or coated steel hinges and operators; stainless for coastal sites

Detailing

Check the sash swing outside: walkways, decks, shutters, and adjacent walls
Place interior screens and window treatments so operators and handles clear them
Use window opening control devices where sills are low above grade on upper floors
Flash rough openings with sill pans and integrate with the WRB
Specify hinge type for egress units so the sash opens far enough for the required clear opening

Uses

Specific uses

Bedrooms needing emergency escape openings
Over kitchen counters, where a crank is easier to reach than a lifting sash
Wind-exposed sites where tight seals matter
High-performance and passive house projects (tilt-turn and triple-glazed casements)
Mulled assemblies with fixed units for ventilation in large glazed walls

Pros and cons

Pros

Full-height ventilation and catches side breezes
Tight compression seal and low air leakage
Easy egress with egress hinges
Clear view with no meeting rail

Cons

Outswing sash can obstruct walkways and is exposed to wind gusts
Sash width limited by hinge strength
Interior screens and operators can conflict with blinds
More hardware and higher cost than sliders and double-hungs

Manufacturing and cost

Construction

Frame and sash extruded, pultruded, or milled; sash glazed with IGU
Hinges, operator, and multipoint lock installed at the factory
Units shipped with nailing fins, brick mold, or as replacement inserts

Main manufacturers and suppliers

Trade associations: Fenestration and Glazing Industry Alliance and Window and Door Manufacturers Association.

Typical costs

Residential casement, installed: $400 to $1,350 per window
Casements run about 10 to 15 percent more than double-hung units of similar size and material

Sources

Fixr: window installation cost breakdown, https://www.fixr.com/articles/window-installation-cost-a-detailed-breakdown
Green Building Advisor: single- vs. double-hung sealing discussion, https://www.greenbuildingadvisor.com/question/single-vs-double-hung-window-ee
FGIA: NAFS-22, https://store.fgiaonline.org/101/I.S.2/A440-22/
FGIA: performance class overview, https://fgiaonline.org/resources/technical-resources/performance-class-overview/
Ecoline Windows: awning, casement, slider, and hung windows compared, https://ecolinewindows.ca/replacement-windows-compared-awning-casement-slider-hung
Wikimedia Commons: Casement window parts.svg, by Cmglee (CC BY-SA 4.0), https://commons.wikimedia.org/wiki/File:Casement_window_parts.svg