{"id":260,"date":"2026-10-28T03:57:07","date_gmt":"2026-10-28T07:57:07","guid":{"rendered":"https:\/\/blackbadgedoors.com\/blogs\/news\/arched-transom-window.html"},"modified":"2026-10-28T03:57:13","modified_gmt":"2026-10-28T07:57:13","slug":"arched-transom-window","status":"publish","type":"post","link":"https:\/\/blackbadgedoors.com\/blogs\/news\/arched-transom-window.html","title":{"rendered":"Arched Transom Window Guide: Shapes, Specs and Glazing"},"content":{"rendered":"<p>You&#039;ve sketched a front door, picked a finish, and now you&#039;re staring at the space above it. You want the curve you saw on a Georgian entry, but you&#039;re not sure what to call it, how to measure it, or whether it&#039;ll leak heat all winter. That&#039;s normal. An <strong>arched transom window<\/strong> looks like a decorative extra, yet it behaves like any other piece of fenestration. Once you name its shape, decide if it should open, and judge the glass and frame as one assembly, the choices get much clearer.<\/p>\n<h2>Table of Contents<\/h2>\n<ul>\n<li><a href=\"#arched-transom-shapes-and-which-one-fits\">Arched Transom Shapes and Which One Fits<\/a><ul>\n<li><a href=\"#the-two-measurements-that-define-it\">The Two Measurements That Define It<\/a><\/li>\n<\/ul>\n<\/li>\n<li><a href=\"#daylight-ventilation-and-proportion-in-everyday-use\">Daylight, Ventilation and Proportion in Everyday Use<\/a><ul>\n<li><a href=\"#four-jobs-one-opening\">Four Jobs, One Opening<\/a><\/li>\n<\/ul>\n<\/li>\n<li><a href=\"#pairing-arched-transoms-with-doors-sidelights-and-facades\">Pairing Arched Transoms with Doors, Sidelights and Fa\u00e7ades<\/a><ul>\n<li><a href=\"#a-pairing-checklist-you-can-hand-over\">A Pairing Checklist You Can Hand Over<\/a><\/li>\n<li><a href=\"#inside-versus-outside\">Inside Versus Outside<\/a><\/li>\n<\/ul>\n<\/li>\n<li><a href=\"#operable-or-fixed-transoms-by-situation\">Operable or Fixed Transoms by Situation<\/a><ul>\n<li><a href=\"#why-fixed-isnt-always-the-efficient-choice\">Why Fixed Isn&#039;t Always the Efficient Choice<\/a><\/li>\n<\/ul>\n<\/li>\n<li><a href=\"#structural-and-code-checks-before-fabrication\">Structural and Code Checks Before Fabrication<\/a><ul>\n<li><a href=\"#safety-glazing-triggers\">Safety Glazing Triggers<\/a><\/li>\n<li><a href=\"#how-the-arch-carries-load\">How the Arch Carries Load<\/a><\/li>\n<\/ul>\n<\/li>\n<li><a href=\"#glazing-and-thermal-choices-for-steel-and-aluminum\">Glazing and Thermal Choices for Steel and Aluminum<\/a><ul>\n<li><a href=\"#steel-versus-aluminum-briefly\">Steel Versus Aluminum, Briefly<\/a><\/li>\n<\/ul>\n<\/li>\n<li><a href=\"#confirm-the-specification-before-you-order\">Confirm the Specification Before You Order<\/a><ul>\n<li><a href=\"#eight-steps-in-order\">Eight Steps, in Order<\/a><\/li>\n<li><a href=\"#a-real-listing-to-calibrate-against\">A Real Listing to Calibrate Against<\/a><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><a id=\"arched-transom-shapes-and-which-one-fits\"><\/a><\/p>\n<h2>Arched Transom Shapes and Which One Fits<\/h2>\n<p>An <strong>arched transom window<\/strong> is a glazed unit set above a door or a larger window, separated from it by a horizontal member, with a curved head instead of a flat top. It sits in the same place a rectangular transom would, but the curve gives the opening a softer, more formal line and usually pushes light a little higher into the room.<\/p>\n<p><a id=\"the-two-measurements-that-define-it\"><\/a><\/p>\n<h3>The Two Measurements That Define It<\/h3>\n<p>Two numbers set the geometry. The <strong>arc radius<\/strong> is the distance from the center of the imaginary circle to the curve itself, so it tells the fabricator how tight the bend is. The <strong>springline<\/strong> is the height where the straight sides stop and the curve starts. Change either one and you change the glass shape, the frame bending, and how the unit meets the wall.<\/p>\n<p>For a half-round, the math is simple because the radius equals half the width and the springline sits at the top of the door frame. For a shallow segmental arc, the radius is much larger than half the width, which is why the rise stays low. Give a fabricator the width, the rise from springline to crown, and the springline height, and they can draw the rest.<\/p>\n<p>In British terminology, this arched form is commonly called a <strong>fanlight<\/strong>, particularly when radial bars divide a semicircular pane like a folding fan. <a href=\"https:\/\/www.bobvila.com\/articles\/transom-windows\/\">Bob Vila&#039;s history of transom windows<\/a> traces that usage through Georgian entrances, where the fanlight became a defining feature above the door.<\/p>\n<p><strong>Arched transom shapes and where each fits<\/strong><\/p>\n\n<figure class=\"wp-block-table\"><table><tr>\n<th>Shape<\/th>\n<th>Arc profile<\/th>\n<th>Typical location<\/th>\n<th>Fabrication note<\/th>\n<\/tr>\n<tr>\n<td>Half-round<\/td>\n<td>Full semicircle, radius equals half the width<\/td>\n<td>Above entry doors with sidelights<\/td>\n<td>Longest frame per square foot of glass, so perimeter sealing needs close attention<\/td>\n<\/tr>\n<tr>\n<td>Segmental<\/td>\n<td>Low-rise arc shorter than a half circle<\/td>\n<td>Tight headroom and flat-ceiling rooms<\/td>\n<td>Simpler radial glazing and less arc length<\/td>\n<\/tr>\n<tr>\n<td>Elliptical<\/td>\n<td>Oval arc, wider than it is tall<\/td>\n<td>Wide openings over double doors<\/td>\n<td>Varying radius, usually needs a full-scale template<\/td>\n<\/tr>\n<tr>\n<td>Eyebrow<\/td>\n<td>Shallow arc spanning a window head<\/td>\n<td>Over windows and interior openings<\/td>\n<td>Shallow rise keeps glass close to flat, so glazing and seals stay simple<\/td>\n<\/tr>\n<tr>\n<td>Mini arch<\/td>\n<td>Smaller radius version of the half-round<\/td>\n<td>Narrow doors and sidelight pairs<\/td>\n<td>Less glass area, smaller radius limits glazing options<\/td>\n<\/tr>\n<\/table><\/figure>\n<p>Choose by headroom first, style second. If you&#039;re working with a full door width plus sidelights and you have the height, a <strong>half-round<\/strong> usually suits because its geometry matches the combined width cleanly. If headroom is tight, a <strong>segmental<\/strong> arc keeps the glass lower, shortens the curved frame, and simplifies fabrication. Write down your shape name, radius, and springline before you ask for a quote. Without those, you&#039;re comparing guesses.<\/p>\n<p><a id=\"daylight-ventilation-and-proportion-in-everyday-use\"><\/a><\/p>\n<h2>Daylight, Ventilation and Proportion in Everyday Use<\/h2>\n<p>In a deep row house, a front room may receive daylight while a middle room has no exterior wall and stays dim with its door closed. A glazed transom above the doorway can pass light between them. If it opens, it can also let air move while the door remains shut. The curved frame is part of the whole opening, so its shape, glazing and operation affect more than appearance.<\/p>\n<p><figure class=\"wp-block-image size-large\"><img decoding=\"async\" src=\"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-content\/uploads\/2026\/10\/arched-transom-window-living-room.jpg\" alt=\"A cozy, well-lit living room featuring a comfortable sofa, a wooden coffee table, and an arched transom window.\" \/><\/figure><\/p>\n<p>In American row houses, rooms could extend <strong>three or four spaces deep<\/strong> from the front or rear fa\u00e7ade, leaving interior rooms without direct daylight or reliable natural ventilation, a pattern described in <a href=\"https:\/\/www.millenniumwindow.com\/transom-window\/\">Millennium Window&#039;s guide to transom windows<\/a>. Operable transoms above interior doors allowed air to circulate with doors closed; fixed glazed versions shared light instead. These functions call for different choices: glass can provide privacy or brightness, while an operable sash adds hardware and a need for convenient access.<\/p>\n<p><a id=\"four-jobs-one-opening\"><\/a><\/p>\n<h3>Four Jobs, One Opening<\/h3>\n<p>A project may ask an arched transom to do one or two of these jobs:<\/p>\n<ol>\n<li><strong>Borrowed light:<\/strong> High glass carries daylight from a brighter room into a hall or interior room, reducing the need for electric lighting during the day.<\/li>\n<li><strong>High-level air movement:<\/strong> Warm air gathers near the ceiling. An opening transom can help vent it into another space or outdoors while the door below stays closed.<\/li>\n<li><strong>Proportion:<\/strong> The arch connects the door, sidelights and wall opening visually, making them read as one composition rather than separate boxes.<\/li>\n<li><strong>Fa\u00e7ade rhythm:<\/strong> Repeated arches create a pattern across an exterior elevation that rectangular heads cannot provide.<\/li>\n<\/ol>\n<p>Georgian and Colonial Revival entrances offer a familiar proportion: a rectangular door below, often paired with sidelights, and a semicircular fanlight above. The door remains practical; the arched glass completes the composition. In an interior, that same curve can make the opening feel taller, but it does not guarantee useful airflow or comfortable temperatures. Those depend on whether the transom opens, where it leads, and how the whole assembly is glazed and sealed.<\/p>\n<blockquote>\n<p>The transom sets where light and air enter. The arch sets how the opening reads.<\/p>\n<\/blockquote>\n<p>Once mechanical air-conditioning became widespread, operable interior transoms lost much of their practical role and largely disappeared from standard construction for decades. Fixed arched fanlights remained in traditional work and later appeared in renovations and custom homes, where their proportions still suit the opening.<\/p>\n<p>Choose the main job before selecting glass or hardware. For borrowed light with privacy, consider whether clear glass would make the room too bright and whether frosted glass better suits the use. For ventilation, plan how the sash will be reached and operated. A fixed transom can serve a daylight or proportion goal, but it cannot provide the airflow of an operable unit.<\/p>\n<p><a id=\"pairing-arched-transoms-with-doors-sidelights-and-facades\"><\/a><\/p>\n<h2>Pairing Arched Transoms with Doors, Sidelights and Fa\u00e7ades<\/h2>\n<p>The most common pairing mistake is simple to spot from the street. The door head sits at one height, the sidelights stop at another, and the arch springs from a third. Nothing lines up, so the entry reads as parts stacked by accident.<\/p>\n<p><figure class=\"wp-block-image size-large\"><img decoding=\"async\" src=\"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-content\/uploads\/2026\/10\/arched-transom-window-front-door.jpg\" alt=\"An elegant black front door with a wreath, surrounded by stone walls, potted hydrangeas, and arched transom window.\" \/><\/figure><\/p>\n<p>Start with alignment. The transom&#039;s <strong>springline and bottom rail<\/strong> must relate clearly to the door head and the tops of any sidelights. In most entries, the bottom rail of the transom is the visual line that caps the door and sidelights together. If that rail floats above the sidelights or cuts across them, the arc will fight everything below it.<\/p>\n<p><a id=\"a-pairing-checklist-you-can-hand-over\"><\/a><\/p>\n<h3>A Pairing Checklist You Can Hand Over<\/h3>\n<ol>\n<li><strong>Set one datum:<\/strong> Put the door head and the transom&#039;s bottom rail on the same horizontal line, and draw the sidelights up to meet it.<\/li>\n<li><strong>Match frame depth and sightlines:<\/strong> Keep the transom frame depth and visible <strong>sightline widths<\/strong> consistent with the sidelights, so one element doesn&#039;t look chunkier than its neighbors.<\/li>\n<li><strong>Align divisions:<\/strong> Line up transom muntins with sidelight muntins or the wider fa\u00e7ade grid. A radial bar that lands on a sidelight stile looks intentional. One that lands mid-pane doesn&#039;t.<\/li>\n<li><strong>Detail the curved-to-rectangular junction:<\/strong> Plan flashing and drainage where a curved head meets a rectangular rough opening, especially above an exterior door where water collects at the springline corners.<\/li>\n<li><strong>Decide how it&#039;s built:<\/strong> Confirm whether the transom arrives as <strong>one manufactured unit<\/strong> with the door assembly or as an arched head assembled above a rectangular window or door frame on site.<\/li>\n<\/ol>\n<p>That last decision affects tolerances. A single manufactured unit arrives with the junction already sealed and squared in the shop. A site-assembled head depends on field shimming at exactly the curved corners where gaps are hardest to see. If you&#039;re exploring how the curve continues inside, our guide to <a href=\"https:\/\/blackbadgedoors.com\/blogs\/news\/arch-glass-doors-interior\">interior arch glass doors<\/a> shows how sightlines carry through interior openings.<\/p>\n<p><a id=\"inside-versus-outside\"><\/a><\/p>\n<h3>Inside Versus Outside<\/h3>\n<p>Exterior and interior pairings fail in different ways. An <strong>exterior<\/strong> unit needs drainage paths, sealed joints, and flashing that sheds water away from the door head. Get that wrong and you&#039;ll chase a leak that looks like a door problem but starts at the arch.<\/p>\n<p>An <strong>interior partition<\/strong> transom has no weather to fight. Its job is light transfer and alignment with trim, so thinner profiles and simpler glazing usually work. Sound privacy matters more than drainage there.<\/p>\n<p>One more constraint overrides preference. On masonry buildings, an existing <strong>brick or stone arch<\/strong> above the opening dictates the curve. The frame must follow the masonry, not the other way around. Measure that curve with a template before anyone quotes the frame, because old masonry arches are rarely perfect semicircles.<\/p>\n<p><a id=\"operable-or-fixed-transoms-by-situation\"><\/a><\/p>\n<h2>Operable or Fixed Transoms by Situation<\/h2>\n<p>Here&#039;s the decision rule in one line. An <strong>operable<\/strong> arched transom gives you ventilation, a <strong>fixed<\/strong> one gives you tighter air sealing and fewer hardware failures, and the right answer depends on climate, location, and who can reach it.<\/p>\n<p>Don&#039;t confuse the two products that look alike in a rendering. A true operable transom is a hinged or pivoted sash with seals, hinges, and a latch or operator. A fixed unit with a decorative divided pattern only looks like it opens. They differ in cleaning access, maintenance, air leakage, and whether they can play any role in ventilation at all.<\/p>\n<p><strong>Operable or fixed arched transom by situation<\/strong><\/p>\n\n<figure class=\"wp-block-table\"><table><tr>\n<th>Situation<\/th>\n<th>Lean toward<\/th>\n<th>Why<\/th>\n<th>What to check<\/th>\n<\/tr>\n<tr>\n<td>Hot climate, stuffy stairwell or upper hall<\/td>\n<td>Operable<\/td>\n<td>Exhausts rising heat at high level<\/td>\n<td>Hardware quality and seal condition<\/td>\n<\/tr>\n<tr>\n<td>Historic building with an originally operable transom<\/td>\n<td>Operable<\/td>\n<td>Preservation guidance favors keeping transoms working<\/td>\n<td>Local historic review<\/td>\n<\/tr>\n<tr>\n<td>Hard-to-reach location or high ceiling<\/td>\n<td>Fixed<\/td>\n<td>Operation becomes impractical<\/td>\n<td>Egress and cleaning access<\/td>\n<\/tr>\n<tr>\n<td>Cold climate with strict air-sealing targets<\/td>\n<td>Fixed, or operable with compression seals<\/td>\n<td>Fewer leak paths<\/td>\n<td>Certified whole-unit air leakage<\/td>\n<\/tr>\n<tr>\n<td>Hurricane or high-wind exposure<\/td>\n<td>Fixed unless operable is documented<\/td>\n<td>Fewer leak points and wind-tested configuration<\/td>\n<td>Product-specific wind and impact documentation<\/td>\n<\/tr>\n<tr>\n<td>Over a door where egress matters<\/td>\n<td>Fixed<\/td>\n<td>Operable sash may not give a usable exit opening<\/td>\n<td>Local egress and safety rules<\/td>\n<\/tr>\n<\/table><\/figure>\n<p><a id=\"why-fixed-isnt-always-the-efficient-choice\"><\/a><\/p>\n<h3>Why Fixed Isn&#039;t Always the Efficient Choice<\/h3>\n<p>You&#039;ll hear that fixed is always more energy efficient. That&#039;s incomplete. A closed operable sash with good <strong>compression seals<\/strong> can perform well, and when you open it on a mild evening it can exhaust rising heat and cut cooling or mechanical ventilation demand. The savings come from not running equipment, and they don&#039;t show up in a laboratory rating that assumes the sash never moves.<\/p>\n<p>The catch is condition. Worn gaskets, a sagging pivoted sash, or a latch that doesn&#039;t pull the sash tight will leak all winter. An operable unit is a small machine at ceiling height, and it needs hardware that&#039;ll hold alignment for years.<\/p>\n<blockquote>\n<p><strong>Practical rule:<\/strong> If nobody can reach it, clean it, and latch it without a ladder and a struggle, don&#039;t make it operable.<\/p>\n<\/blockquote>\n<p>Preservation adds a different pressure. Where a historic transom was built to open, reviewers often want it working again rather than sealed shut. Hurricane exposure pushes the other way, toward fixed units, unless the exact operable configuration carries its own tested documentation.<\/p>\n<p>Ask three questions and you&#039;ll usually have your answer. Who will open it? How high is it? What will it need to seal well in January, not just on installation day?<\/p>\n<p><a id=\"structural-and-code-checks-before-fabrication\"><\/a><\/p>\n<h2>Structural and Code Checks Before Fabrication<\/h2>\n<p>A decorative arch is not exempt from fenestration rules. That&#039;s the assumption to drop first. Your arched transom window still has to satisfy safety glazing, structural loading, and weather requirements, and the curve makes some of those checks harder, not easier.<\/p>\n<p><figure class=\"wp-block-image size-large\"><img decoding=\"async\" src=\"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-content\/uploads\/2026\/10\/arched-transom-window-safety-glazing-codes.jpg\" alt=\"An infographic detailing essential structural and safety code requirements for window glazing prior to manufacturing.\" \/><\/figure><\/p>\n<p><a id=\"safety-glazing-triggers\"><\/a><\/p>\n<h3>Safety Glazing Triggers<\/h3>\n<p>In residential work, safety glazing is required in several hazardous locations, including glazing near doors, glazing with its bottom edge <strong>within 18 inches of the floor<\/strong>, stair enclosures and guards, and specified tub or shower locations, as summarized in the <a href=\"https:\/\/www.wellstown.org\/DocumentCenter\/View\/8143\/2021-IRC-Common-Questions\">2021 IRC common questions document<\/a>. Read that list against your own opening:<\/p>\n<ul>\n<li><strong>Near a door:<\/strong> A transom directly above a swinging door sits in the zone reviewers examine first.<\/li>\n<li><strong>Low bottom edge:<\/strong> A tall arched unit over a window can dip lower than you expect at its edges.<\/li>\n<li><strong>Stairs and guards:<\/strong> Glass beside a landing or forming part of a guard gets extra scrutiny.<\/li>\n<li><strong>Wet locations:<\/strong> Arched glass over a tub or shower door falls under its own specified locations.<\/li>\n<\/ul>\n<p>Whether your transom needs <strong>safety glazing<\/strong> depends on its location, dimensions, and relationship to the door opening. Make that call from the adopted local code and the final shop drawings, not from a catalog photo. State rules also vary, so if your project sits in that jurisdiction, <a href=\"https:\/\/usasuperior.com\/utah-building-codes\/\">check Utah window replacement rules<\/a> before you assume a national summary covers you.<\/p>\n<p><a id=\"how-the-arch-carries-load\"><\/a><\/p>\n<h3>How the Arch Carries Load<\/h3>\n<p>Straight frames push wind pressure and glass weight into jambs in predictable ways. A curve spreads those forces along bent or segmented members, curved muntins, and often <strong>narrow steel profiles<\/strong> chosen for their slim look. Those members still have to transfer load into the jambs, the head, and the surrounding wall.<\/p>\n<p>They can&#039;t lean on finish materials or a flexible door header. Drywall, casing, and a bouncy header will let the frame deflect, the seals will open at the corners of the springline, and the glass will carry stress it wasn&#039;t sized for.<\/p>\n<p>Before fabrication, ask for a short package:<\/p>\n<ul>\n<li><strong>Engineered attachment details:<\/strong> How the curved frame anchors into structure, and at what spacing.<\/li>\n<li><strong>Design-pressure criteria:<\/strong> The wind load for your site&#039;s exposure, not a generic value.<\/li>\n<li><strong>Glass make-up:<\/strong> Thickness, tempering or lamination, and how the curved lite is supported.<\/li>\n<li><strong>Allowable deflection limits:<\/strong> How much movement the frame can tolerate before seals or glass suffer.<\/li>\n<li><strong>Wind or impact documentation:<\/strong> For coastal or high-wind sites, paperwork for the specific size, configuration, glazing, anchorage, and operating condition.<\/li>\n<\/ul>\n<p>Don&#039;t infer impact compliance from appearance. A heavy frame in a brochure tells you nothing about your width, your anchorage, or your glass.<\/p>\n<p>Work in sequence. Freeze the <strong>rough opening and arch geometry<\/strong> first. Then coordinate structural support, safety glazing, weather sealing, and finish tolerances. Fabricate last. Thermal documentation feeds into this review as a code input, and the next set of choices covers how to judge it.<\/p>\n<p><a id=\"glazing-and-thermal-choices-for-steel-and-aluminum\"><\/a><\/p>\n<h2>Glazing and Thermal Choices for Steel and Aluminum<\/h2>\n<p>Judge an arched transom window as a <strong>whole assembly<\/strong>, not by the glass at the center of the pane. The center is the best-performing square inch of the unit. The edges, the spacer, and that long curved frame are where heat escapes.<\/p>\n<p>The <strong>NFRC U-factor<\/strong> includes the glazing, frame, and spacers, and a lower U-factor indicates lower heat transfer, according to the <a href=\"https:\/\/www1.eere.energy.gov\/buildings\/publications\/pdfs\/building_america\/measure_guide_windows.pdf\">U.S. Department of Energy window measure guide<\/a>. That matters more for an arch than for a rectangle because the curved perimeter contains <strong>more frame length relative to glass area<\/strong>, so conductive frame loss and thermal bridging claim a bigger share of the total.<\/p>\n<p>So compare whole-unit numbers, not center-glass claims. Ask for U-factor, <strong>solar heat-gain coefficient (SHGC)<\/strong>, visible transmittance, air leakage, and condensation resistance for the exact size and shape you&#039;re buying. Our comparison of <a href=\"https:\/\/blackbadgedoors.com\/blogs\/news\/double-vs-triple-glazing\">double versus triple glazing<\/a> walks through when the third pane earns its weight and cost.<\/p>\n<p><strong>Glazing and frame choices by climate or exposure<\/strong><\/p>\n\n<figure class=\"wp-block-table\"><table><tr>\n<th>Climate or exposure<\/th>\n<th>Glazing<\/th>\n<th>Frame<\/th>\n<th>Figure to request<\/th>\n<\/tr>\n<tr>\n<td>Cold and mixed climates<\/td>\n<td>Double or triple low-e insulated glass with inert gas fill<\/td>\n<td>Thermally broken steel or aluminum<\/td>\n<td>Whole-unit NFRC U-factor<\/td>\n<\/tr>\n<tr>\n<td>Hot, sunny exposure<\/td>\n<td>Low-e glass selected for lower solar gain<\/td>\n<td>Thermally broken frame<\/td>\n<td>NFRC SHGC and visible transmittance<\/td>\n<\/tr>\n<tr>\n<td>Coastal or hurricane zone<\/td>\n<td>Impact-rated or wind-tested glazing as documented<\/td>\n<td>Impact-rated steel or aluminum system<\/td>\n<td>Product-specific wind or impact certification<\/td>\n<\/tr>\n<tr>\n<td>Historic district<\/td>\n<td>Pane pattern matching the original<\/td>\n<td>Profile and finish matching the original<\/td>\n<td>Local historic review approval<\/td>\n<\/tr>\n<tr>\n<td>Interior partition with no thermal load<\/td>\n<td>Tempered or single glazing<\/td>\n<td>Light steel or aluminum profile<\/td>\n<td>Safety glazing marking<\/td>\n<\/tr>\n<\/table><\/figure>\n<p>In cold and mixed climates, the relevant combination is <strong>thermally broken framing plus low-e insulated glazing<\/strong>. Multiple panes, low-emittance coatings, inert-gas fills, and less-conductive frame construction each reduce thermal transmittance, and on a curved steel unit the thermal break does heavy lifting because steel conducts heat so readily.<\/p>\n<p><a id=\"steel-versus-aluminum-briefly\"><\/a><\/p>\n<h3>Steel Versus Aluminum, Briefly<\/h3>\n<p><strong>Steel<\/strong> gives you slim sightlines and sturdy curved sections, which is why architects reach for it when the arch needs to look delicate but span wide. <strong>Aluminum<\/strong> is lighter and resists corrosion without relying on coatings, which helps in coastal air and on large units that crews have to lift into place. Both need a thermal break on an exterior, conditioned opening. Neither performs well as a solid, unbroken metal path from inside to outside.<\/p>\n<p>Specify the details that change the tested assembly:<\/p>\n<ul>\n<li><strong>Exact geometry:<\/strong> Arch radius, springline, and overall size.<\/li>\n<li><strong>Glazing build:<\/strong> Pane thickness, coating, gas fill, and <strong>spacer type<\/strong>.<\/li>\n<li><strong>Frame build:<\/strong> Material and thermal-break configuration.<\/li>\n<\/ul>\n<blockquote>\n<p>A strong glass number can&#039;t rescue a broken perimeter seal. Cold air doesn&#039;t read spec sheets.<\/p>\n<\/blockquote>\n<p>Field installation can undo good specification. Uneven shimming twists a curved frame, and a discontinuous perimeter seal creates localized <strong>air leakage and condensation<\/strong> even when the glass rating looks strong. That&#039;s why <a href=\"https:\/\/h-towneremodelers.com\/energy-efficient-double-pane-window-installation\/\">proper installation for energy-saving windows<\/a> matters as much as the unit itself, and why you should request shop drawings, certified whole-unit values, condensation-resistance data, and sealant details before you approve anything.<\/p>\n<p><a id=\"confirm-the-specification-before-you-order\"><\/a><\/p>\n<h2>Confirm the Specification Before You Order<\/h2>\n<p>Ordering is the last step, not the first. An arched unit can&#039;t be trimmed to fit on site the way a rectangular frame can hide behind casing, so the procedure below protects you from the most expensive mistake in this category, which is a beautiful arch built to the wrong curve.<\/p>\n<p><figure class=\"wp-block-image size-large\"><img decoding=\"async\" src=\"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-content\/uploads\/2026\/10\/arched-transom-window-measurement-guide.jpg\" alt=\"A four-step infographic illustrating how to measure and verify an arched window opening before placing an order.\" \/><\/figure><\/p>\n<p><a id=\"eight-steps-in-order\"><\/a><\/p>\n<h3>Eight Steps, in Order<\/h3>\n<ol>\n<li><strong>Measure in the field:<\/strong> Record width, rise, radius, and springline from the built opening, because plans often differ from what&#039;s framed or laid in masonry.<\/li>\n<li><strong>Choose shape and operation:<\/strong> Use your headroom to pick the arc, then decide operable or fixed based on reach, climate, and sealing targets.<\/li>\n<li><strong>Pick the frame material:<\/strong> Choose steel for slim sightlines and custom profiles, or aluminum where impact or coastal rules drive the specification.<\/li>\n<li><strong>Set glazing targets:<\/strong> Fix the whole-unit U-factor, SHGC, glass type, and gas fill for your climate zone before anyone prices the unit.<\/li>\n<li><strong>Confirm code and historic review:<\/strong> Verify safety glazing locations, design wind pressure, and any district requirements for pane pattern, profile, and finish.<\/li>\n<li><strong>Request the paper package:<\/strong> Get shop drawings, certified whole-unit ratings, attachment details, and sealant details in writing.<\/li>\n<li><strong>Check tolerances and sequence:<\/strong> Confirm shimming, perimeter seals, and which trade handles structure and weather sealing, and in what order.<\/li>\n<li><strong>Order against the drawings:<\/strong> Release fabrication only when the shop drawings match your field measurements exactly.<\/li>\n<\/ol>\n<p>If you&#039;re new to ordering to size, our overview of <a href=\"https:\/\/blackbadgedoors.com\/blogs\/news\/custom-dimensions\">custom dimensions for steel doors and windows<\/a> explains how field measurements become shop drawings.<\/p>\n<p><a id=\"a-real-listing-to-calibrate-against\"><\/a><\/p>\n<h3>A Real Listing to Calibrate Against<\/h3>\n<p>Custom quotes are easier to judge with one real reference point. In 2026, the <a href=\"https:\/\/www.auroramills.com\/shop\/p\/arched-wreath-and-ribbon-transom\">Aurora Mills arched transom listing<\/a> offered a unit measuring <strong>76 inches wide, 17 inches tall, and 1.75 inches thick, weighing 30 pounds, for $1,595<\/strong>. That&#039;s a shallow, wide piece, closer to an eyebrow than a half-round. Use it to sanity-check size, weight, and price, then expect a thermally broken, insulated, custom steel assembly to land differently.<\/p>\n<p>One decision deserves a final pause. The National Park Service rehabilitation guidance on energy cautions against replacing historic transoms with fixed thermal glazing or leaving them inoperable when they can contribute to a building&#039;s energy-conserving design. If your transom was built to open, price the operable version with compression seals, drainage, and good hardware before you default to fixed.<\/p>\n<p>For a custom steel arch, we offer a <strong>Steel Arch Glass Door<\/strong> that&#039;s also available as a mini arch and as a double door full arch, with all steel metal construction, custom finishes and RAL colors, and European hardware. If your project sits in a northern climate, a thermally broken version of our picture window is available through a custom quote. Whatever you choose, ask for whole-unit ratings before you commit. A center-glass number is not a specification.<\/p>\n<hr>\n<p>If you&#039;re ready to turn your field measurements, radius, and springline into shop drawings for a custom arched transom window or steel arch door, visit <a href=\"https:\/\/blackbadgedoors.com\">Black Badge Doors<\/a> to explore made-to-order steel and aluminum options and request a quote. Bring your climate zone, target U-factor, and opening dimensions, and we&#039;ll help you confirm the specification before fabrication starts.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>You&#039;ve sketched a front door, picked a finish, and now you&#039;re staring at the space above it. You want the curve you saw on a Georgian entry, but you&#039;re not sure what to call it, how to measure it, or whether it&#039;ll leak heat all winter. That&#039;s normal. An arched transom window looks like a [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":259,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[181,185,184,183,182],"class_list":["post-260","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized","tag-arched-transom-window","tag-custom-window-specification","tag-fanlight-window","tag-steel-transom-window","tag-transom-window-design"],"_links":{"self":[{"href":"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-json\/wp\/v2\/posts\/260","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-json\/wp\/v2\/comments?post=260"}],"version-history":[{"count":1,"href":"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-json\/wp\/v2\/posts\/260\/revisions"}],"predecessor-version":[{"id":265,"href":"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-json\/wp\/v2\/posts\/260\/revisions\/265"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-json\/wp\/v2\/media\/259"}],"wp:attachment":[{"href":"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-json\/wp\/v2\/media?parent=260"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-json\/wp\/v2\/categories?post=260"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blackbadgedoors.com\/blogs\/news\/wp-json\/wp\/v2\/tags?post=260"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}