Window Styles Explained: Casement, Double-Hung, Awning, Slider, and Which Ones Can Legally Be a Bedroom Escape Window

Last reviewed: 2026-09-27

Researched and written by one person, not an editorial team. I am an independent researcher, not a licensed contractor, and I do not install windows — see the About page for exactly what I do and don't do. This page is a pure style comparison; there is no lead form on it, and nothing on this page routes you to one. The site earns money elsewhere by referring homeowners who submit a form to a disclosed set of installers and lead networks — disclosed on those pages, not here, because there's no form here to disclose the disposition of. I don't make "best installer in [city]" recommendations and I don't rank contractors. Everything below is sourced from manufacturer spec sheets, cost surveys, and the International Residential Code; nothing here is hands-on testing of a physical unit.

Why "which window style is best" is the wrong question again

This site's material comparison page already made the case that "best" collapses a decision that actually splits by climate, budget, and maintenance tolerance — for material (vinyl, fiberglass, wood, composite). This page asks the same question about a different, mostly-independent variable: operating style. You can buy a fiberglass casement or a fiberglass double-hung; the material decision and the style decision are separate, and conflating them is why so many "best windows" pages give useless answers. Style decides how the sash moves, how tightly it can seal when closed, how much of the opening actually admits air when open, whether it can legally serve as a bedroom's required emergency exit, and — independent of material — how much it costs.

The eight styles, and what "operable" means for each

Style	How it opens	Ventilation when open	Typical placement
Double-hung	Both sashes slide vertically past each other	Roughly half the total glass area at most	Anywhere; the default residential style
Single-hung	Bottom sash slides up; top sash fixed	Roughly half the total glass area	Budget-tier replacement of double-hung
Casement	Whole sash cranks outward on a hinge, like a door	Up to 90–100% of the opening	Over sinks/counters; hard-to-reach spots
Awning	Hinged at the top, cranks outward from the bottom	Full width of the opening, admits air even in light rain	High on walls, above other windows, bathrooms
Slider (gliding)	One or more sashes slide horizontally in a track	Roughly half the total glass area	Wide, low openings
Picture (fixed)	Does not open at all	None	Combined with operable units for light
Bay / bow	An assembly of 3 (bay) or 4–6+ (bow) angled/curved units, usually a mix of fixed and operable	Depends entirely on which of the individual units in the assembly are operable	Projecting from an exterior wall
Hopper	Hinged at the bottom, tilts inward from the top	Full width, but into the room	Basements, small high openings

This table alone is why "compare window styles" articles that just list adjectives ("casement: great ventilation!") miss the two things that actually change your decision: how tightly a style seals when closed (next section) and whether it can legally be your only way out of a bedroom (the section after that).

The physical mechanism: why a casement seals tighter than a double-hung or slider

A double-hung or slider sash rides in a track and is held closed by gravity, a lock, and a strip of weatherstripping compressed by the sash's own weight or a spring balance. A casement or awning sash is different: a crank mechanism physically pulls the entire sash inward against the frame when you close it, compressing a continuous weatherstrip seal around all four sides simultaneously — the same physical principle as a refrigerator door gasket, not a sliding drawer.

Marvin, a manufacturer, states this plainly and backs it with NFRC-tested air-leakage numbers for its own products (retrieved 2026-09-27):

"The locking mechanism on Marvin casement windows are designed to pull the sash in tight, which creates a consistent compression of the weather stripping around the entire perimeter" — and the company's Ultimate Casement is rated at less than 0.01 cfm/ft² air infiltration. By contrast, sliding/glider windows "can be more susceptible to air infiltration" because they lack "check rail engagement or sill interlock," and double-hung windows underperform casements because they "do not have the same locking mechanism that sucks the entire sash in tight" and carry "more seams and linear feet of weather-stripping."

Source: Marvin, "What You Need to Know About Air Infiltration", retrieved 2026-09-27. Take the specific comparative framing as a manufacturer's own description of its casement product's advantage over its own double-hung and slider lines — it's a real physical mechanism (a compression-sealed hinge vs. a sliding sash), not an independently audited third-party lab comparison across brands. For scale: ENERGY STAR's own maximum air-leakage requirement is 0.3 cfm/ft² for windows and sliding doors (0.5 cfm/ft² for swinging doors), per the same EPA specification cited throughout this site's other pages — meaning even a "leaky" double-hung that clears ENERGY STAR at all is still well under the ceiling; the casement-vs-double-hung gap described above is a performance difference well inside the certified range, not a pass/fail difference.

A same-manufacturer, same-glazing comparison table across three styles

Marketing pages compare styles in adjectives. To compare them in numbers, I pulled the actual NFRC glazing-performance tables from Pella's Architectural Design Manual for three product lines and matched rows with the identical named glazing package and, where possible, the identical gap width, so the U-factor and SHGC differences below reflect the frame/sash design, not a different glass package being compared across styles. Casement and double-hung are both Pella's Impervia (fiberglass) line; awning is Pella's Reserve (aluminum-clad wood) line, because Pella's ADM does not publish an Impervia awning table with directly matching glazing names — noted as a caveat in the table itself, not hidden.

Property	Impervia Casement	Impervia Double-Hung	Reserve Awning (clad-wood, different material)
Clear IG, 3mm/3mm air gap — U-factor / SHGC	0.44 / 0.55	0.48 / 0.58	0.46 / 0.57 (3mm/3mm, aluminum-clad wood)
Advanced Low-E IG, 3mm/3mm argon — U-factor / SHGC	0.28 / 0.26	0.31 / 0.28	0.29 / 0.27
Condensation Resistance (CR), Advanced Low-E row	60	57	56
Air leakage (manufacturer-stated, compression vs. track seal)	< 0.01 cfm/ft² (Marvin Ultimate Casement, comparable mechanism)	Higher; no compression seal	Comparable to casement (also a compression-sealed hinge)
ENERGY STAR US zones met at the Advanced Low-E row shown	None shown shaded at this specific row (fails Northern/North-Central on U-factor; fails SHGC cap for South-Central/Southern)	Same — none shaded at this row	Same
Frame material in table shown	Fiberglass	Fiberglass	Aluminum-clad wood

Sources: Pella Corporation, "Impervia® Casement Windows" Architectural Design Manual (PDF) · Pella Corporation, "Impervia® Double-Hung Windows" Architectural Design Manual (PDF) · Pella Corporation, "Pella® Reserve™ Traditional Awning Window" Architectural Design Manual (PDF), all retrieved 2026-09-27 — primary-document extraction; none of these per-configuration NFRC numbers appear on Pella's consumer-facing product pages, only in the dealer-facing ADM PDFs.

Two things this table shows that a materials page or a marketing adjective can't:

At an identical glazing package, the casement consistently beats the double-hung on U-factor — 0.44 vs. 0.48 at the base Clear IG package, 0.28 vs. 0.31 at the upgraded Low-E package. That's the compression seal reducing frame-level heat loss, not just air infiltration — the U-factor is a whole-unit measurement, so a tighter seal shows up in it directly.
The awning window (a different material line entirely) tracks much closer to the casement than to the double-hung — 0.46/0.29 vs. the casement's 0.44/0.28, despite being wood-core rather than fiberglass. That's consistent with the compression-seal mechanism being the driver, not the frame material: awning and casement sashes both crank shut against a continuous seal; double-hung and slider sashes don't.

None of the specific rows shown above happen to clear a shaded ENERGY STAR zone at the glazing package level I selected for the cleanest cross-style comparison — Pella's ADM documents shade zones further down each table at higher-performance (SunDefense / SunDefense+) glazing packages, which trade some visible light transmittance for a lower SHGC. The takeaway isn't "these specific windows fail ENERGY STAR" — it's that the specific glazing package, not just the frame style, decides zone qualification, which is exactly the point the U-factor and SHGC explainer on this site goes into in more depth.

Cost by style

Style	This Old House per-window average	Fixr range
Single-hung	$474	—
Casement	$529	$200–$2,400 ($400–$1,200 typical)
Sliding	$531	—
Picture	$540	—
Awning	$545	—
Bay	$550	—
Double-hung	$551	—
Glass block	$505	—
Bow	—	$1,500–$8,000
Garden	—	$1,000–$4,000
Hopper	Not priced by either source	Not priced by either source

Sources: This Old House, "Window Replacement Cost (2026)" (updated 2026-08-11) and Fixr.com, "Cost to Install Casement Windows in 2026" (published 2026-01-30) and Fixr.com, "How Much Does Window Replacement Cost in 2026?" (published 2026-01-21), all retrieved 2026-09-27.

This Old House's eight priced styles cluster tightly — $474 to $551, an average of $517 — which tells you that for a standard-size single unit, style alone is a minor cost lever compared to material, size, and glazing package (the variables the entry-door and window cost pages on this site found doing most of the work). Bay, bow, and garden windows break that pattern because they aren't single units — they're multi-unit assemblies with their own framing and roof/support structure, which is why Fixr's bow-window range ($1,500–$8,000) reaches several times higher than any single-unit style above it.

Egress: which styles can — and structurally cannot — be a bedroom's required exit

This is the section a materials or style page usually skips, and it's governed by an actual, quotable code section: IRC R310, Emergency Escape and Rescue Openings. I read the code text directly rather than paraphrasing a summary blog.

"Basements, habitable attics and every sleeping room shall have not less than one operable emergency escape and rescue opening." — IRC R310.1 (2021 edition), retrieved 2026-09-27.

The opening — whichever window is designated to satisfy this — must meet all four of the following simultaneously (retrieved 2026-09-27, primary-document extraction from the 2021 IRC text, R310.1.1 and R310.2.1–R310.2.2):

Minimum net clear opening: 5.7 square feet (5 square feet if the opening is at grade floor level).
Minimum net clear height: 24 inches.
Minimum net clear width: 20 inches.
Maximum sill height above the finished floor: 44 inches.
The opening must be "operational from the inside of the room without the use of keys, tools or special knowledge" (R310.1.1).

"Net clear opening" is the operative phrase — it's the usable opening when the window is fully operated open, measured by "the normal operation of the emergency escape and rescue opening from the inside," not the frame size, not the glass area, and not the rough opening in the wall. This is exactly where operating style stops being a preference question and becomes a pass/fail one:

Casement windows are the style that most reliably clears egress in a standard size, because the sash swings fully open on a hinge — the net clear opening is close to the full glass area of the sash, so even a moderately sized casement clears both the 5.7 sq ft area and the 20-inch width requirement.
Double-hung and single-hung windows must be sized so that half the sash opening (since only one sash moves, or both move but only overlap to half height) still clears 5.7 sq ft and 20 inches wide — a narrow double-hung that looks adequately sized closed can fail net clear opening when you do the math on what actually clears when it's raised.
Sliding windows face the same halving problem — typically only one of two (or one of three) panels slides, so only that panel's opening counts toward the 20-inch minimum width and 5.7 sq ft area, not the window's total width.
Awning and hopper windows hinge on one edge and open at an angle rather than swinging fully clear, which frequently limits the net clear opening even when the window's total glass area looks large enough on paper — the hinge-side dimension doesn't fully open, so it doesn't count toward the usable rescue opening the same way a casement's does.
Picture (fixed) windows can never satisfy R310 on their own — they don't operate at all, which fails the threshold requirement in R310.1 before any dimension is even checked.
Bay and bow window assemblies are typically a mix of fixed and operable units. Whether the assembly can satisfy egress depends entirely on whether one of its individual operable units, by itself, clears all four requirements above — the fixed picture-window center panel that's standard in most bay and bow configurations cannot, and the angled side units are often narrower than the 20-inch minimum width even when operable.

None of this is a style ranking — it's a constraint that only binds in specific rooms (sleeping rooms, basements, habitable attics) and only for whichever single opening in that room is designated as the required egress window. A bedroom can have a beautiful fixed picture window and a bay window and still be code-compliant, as long as one other opening in the room — often a companion casement or an appropriately-sized double-hung — independently clears R310. The practical implication for a remodel: if you're replacing the one window in a bedroom that currently serves as its emergency exit, get the replacement's net clear opening checked against R310 explicitly, in writing, before installation — not just the frame size against the old frame size. A same-size replacement can still fail egress if the new unit's operable mechanism reduces the net clear opening compared to the old one (a slider swapped in for an old casement is the failure mode most likely to catch a homeowner by surprise).

Sources: ICC 2021 International Residential Code, Section R310, as mirrored at up.codes and up.codes, R310.1 Emergency Escape and Rescue Opening Required and up.codes, R310.2.2 Window Sill Height, retrieved 2026-09-27 — up.codes republishes ICC code text; I did not access the ICC's own paywalled codes.iccsafe.org hosting directly. Local jurisdictions frequently adopt the IRC with state-specific amendments — always confirm the exact edition and any local amendment your jurisdiction has adopted before relying on the figures above for a permit application.

What we could not verify

Exact per-jurisdiction egress amendments. The IRC is a model code; states and municipalities adopt it with local amendments, and R310's specific numbers have changed slightly across IRC editions (2015, 2018, 2021, 2024). I cited the 2021 edition's text as mirrored by up.codes and did not independently confirm every state's currently adopted edition or local amendments — check your specific jurisdiction's adopted code before relying on these numbers for a permit.
Independent third-party air-infiltration testing across brands. The casement-vs-double-hung-vs-slider air-leakage comparison in this article comes from Marvin's own blog describing Marvin's own product lines. It's consistent with the compression-seal-vs-track-seal physical mechanism, and the specific numbers cited (Marvin Ultimate Casement, under 0.01 cfm/ft²) are NFRC-tested, but I did not find an independent lab study comparing the same metric across multiple manufacturers' double-hung, slider, and casement product lines side by side.
A same-material-line, same-glazing awning comparison. Pella's Architectural Design Manual does not publish an Impervia (fiberglass) awning table with glazing package names matching the Impervia casement and double-hung tables, which is why the awning row above uses the Reserve (aluminum-clad wood) line instead — a real but imperfect comparison, flagged in the table itself.
A specific NFRC air-leakage (AL) rating for Pella's Impervia casement and double-hung lines. The Impervia ADM tables I extracted report U-factor, SHGC, VLT, and Condensation Resistance, but not a per-row Air Leakage (AL) figure; I used Marvin's published casement/double-hung comparison for the air-infiltration claim instead, which is a different manufacturer's product, not Pella's.
Hopper window installed cost. Neither This Old House nor Fixr publishes a specific hopper-window cost figure; I did not find another source with a citable number and left it out rather than estimate one.

Sources

All retrieved 2026-09-27 unless noted.

Marvin, "What You Need to Know About Air Infiltration"
Pella Corporation, "Impervia® Casement Windows" Architectural Design Manual (PDF) (primary-document extraction)
Pella Corporation, "Impervia® Double-Hung Windows" Architectural Design Manual (PDF) (primary-document extraction)
Pella Corporation, "Pella® Reserve™ Traditional Awning Window" Architectural Design Manual (PDF) (primary-document extraction)
U.S. EPA, "ENERGY STAR Product Specification, Residential Windows, Doors, and Skylights, Final Draft Version 7.0" (primary-document extraction — Table 5, Air Leakage Requirements)
This Old House, "Window Replacement Cost (2026)"
Fixr.com, "Cost to Install Casement Windows in 2026"
Fixr.com, "How Much Does Window Replacement Cost in 2026?"
up.codes, "R310.1 Emergency Escape and Rescue Opening Required" (2021 IRC text) (primary-document extraction)
up.codes, "R310.2.1 Minimum Opening Area" (2021 IRC text) (primary-document extraction)
up.codes, "R310.2.2 Window Sill Height" (2021 IRC text) (primary-document extraction)
Fenplast, "Emergency exit Code (Egress)" — secondary corroboration that bay/bow angled units commonly fail net-clear-opening egress requirements
This site, Vinyl vs Fiberglass vs Wood Windows — cross-referenced for the materials-vs-style framing
This site, Window Replacement Cost in 2026 — cross-referenced for general per-window cost context
This site, U-factor and SHGC Explained — cross-referenced for the ENERGY STAR zone-qualification detail
Marvin, "Elevate and Essential Product Performance" Architectural Detail Manual (PDF) — consulted for cross-checking the ENERGY STAR US criteria restatement; not directly quoted in this article