Reviewed by The Roofing Brief Team. Last reviewed: October 2026.
Custom skylights fall into two buckets: a stock skylight built to a non-catalog opening, such as a VELUX FCM custom size up to 50-3/4 by 76-1/2 inches, and a made-to-order glazing unit (circles, pyramids, polygons, walkable glass) from a specialty manufacturer. The first prices close to a standard skylight, which HomeGuide’s skylight cost guide (August 2025) puts at $1,500 to $4,000 installed for a fixed unit. The second is quoted per project; HomeGuide lists custom-built glass roof canopies at $3,000 to $7,000 or more each. Knowing which one you need sets both the budget and the lead time.
What “custom skylights” actually means (two different products)
The phrase “custom skylights” gets used for two products that share almost nothing on price or lead time. One is a stock skylight resized to your opening: the VELUX FCM technical data sheet (V5074-0921) lists 14 standard size codes plus custom make sizes from 18-3/4 inches up to 50-3/4 inches wide and 76-1/2 inches long. The other is a bespoke glass assembly engineered for your roof, from firms such as Marco Skylights, which says all of its skylights are built to size, or Solar Innovations, whose single-slope skylights are offered on any roof pitch and in nearly any size.
| Type | What it is | Who makes it | Typical use |
|---|---|---|---|
| Custom size | A standard skylight (usually curb mounted) built to a non catalog width and length | VELUX (FCM custom), Sun-Tek, Wasco | An opening that does not match a stock size code, or a slightly larger daylight area |
| Custom shape | A made to order unit in a non rectangular shape: circle, octagon, triangle, trapezoid, pyramid, ridge | Marco, Glazing Vision, CrystaLite, Supreme, Sun Valley | Architectural rooflines, atriums, dramatic daylighting |
| Structural glazing | Walkable, drive over, or large span glass engineered as part of the structure | Glazing Vision and other architectural glazing firms | Roof decks, floor lights, spans past 10 feet |
Custom skylights decision table: which route fits your opening
| If your opening or roof is | Choose | Rule or source |
|---|---|---|
| Within 1/2 inch of a VELUX size code (for example 2246 = 22-1/2 x 46-1/2 in inside curb) | Standard FCM from stock | VELUX FCM data sheet and current VELUX pro size list |
| Between stock sizes, make size 18-3/4 to 50-3/4 in wide and up to 76-1/2 in long | VELUX FCM custom size | VELUX FCM data sheet; about 4 to 5 weeks lead time per OC Skylights, a VELUX dealer |
| Rectangular but longer than 76-1/2 in | VELUX Large Span (up to 10 ft long) or a specialty maker | VELUX Large Span product page |
| Round, pyramid, polygon or ridge shape | Specialty manufacturer, quoted to a drawing | Marco, Solar Innovations, CrystaLite product lines |
| Walk-on or drive-over glass | Structural glazing engineered per project | Glazing Vision Flushglaze Walk On range |
| Flat roof with an acrylic dome | Custom dome fabricated to the curb | OC Skylights quotes 1 to 2 weeks for custom domes |
| Roof slope under 3:12 | Curb mount at least 4 in above the roof plane | IRC R308.6.8, unless the maker’s instructions say otherwise |
| Florida high-velocity hurricane zone | Impact glazing (FCM “Impact”: 2.3 mm laminated, 2.28 mm interlayer) | VELUX data sheet lists Florida Product Approval 13303 HVHZ |
Standard skylight sizes vs custom sizes (VELUX FCM chart)
The VELUX FCM size code reads as inside-curb width then length in inches, rounded down: a 2246 fits a curb measuring 22-1/2 by 46-1/2 inches inside. Check this chart before ordering a custom unit, because a curb that misses a code by an inch can often be reframed for less than the custom upcharge.
| FCM size code | Inside curb (in) | Outside curb (in) | Source |
|---|---|---|---|
| 1430 | 14-1/2 x 30-1/2 | 17-1/2 x 33-1/2 | VELUX FCM data sheet |
| 1446 | 14-1/2 x 46-1/2 | 17-1/2 x 49-1/2 | VELUX FCM data sheet |
| 2222 | 22-1/2 x 22-1/2 | 25-1/2 x 25-1/2 | VELUX FCM data sheet |
| 2246 | 22-1/2 x 46-1/2 | 25-1/2 x 49-1/2 | VELUX FCM data sheet |
| 2270 | 22-1/2 x 70-1/2 | 25-1/2 x 73-1/2 | VELUX FCM data sheet |
| 3030 | 30-1/2 x 30-1/2 | 33-1/2 x 33-1/2 | VELUX FCM data sheet |
| 3446 | 34-1/2 x 46-1/2 | 37-1/2 x 49-1/2 | VELUX FCM data sheet |
| 4646 | 46-1/2 x 46-1/2 | 49-1/2 x 49-1/2 | VELUX FCM data sheet |
| 4672 | 46-1/2 x 72-1/2 | 49-1/2 x 75-1/2 | VELUX FCM data sheet |
| Custom FCM | Make size 18-3/4 to 50-3/4 wide, 18-3/4 to 76-1/2 long | VELUX FCM data sheet | |
The other standard codes on the sheet are 2230, 2234, 3046, 3055 and 3434. The custom ceiling of 50-3/4 by 76-1/2 inches is essentially the envelope of the largest stock unit (4672 make size 50-5/8 by 76-5/8 inches), so a VELUX FCM custom size fills the gaps between stock codes rather than going bigger. For deck mounted size codes, see our VELUX skylight size chart.
How much do custom skylights cost?
A standard fixed skylight is the price anchor: HomeGuide (August 2025) lists $150 to $800 for the unit and $1,500 to $4,000 installed, and $1,350 to $5,400 installed for VELUX fixed or venting models. A VELUX FCM custom size is a dealer quote rather than a list price; US Building Products, a VELUX dealer, takes custom FCM orders through a quote form. Large and shaped glazing is where the price climbs: HomeGuide lists extra-large round units 60 to 90 inches wide at $1,200 to $5,800 each and custom-built glass roof canopies at $3,000 to $7,000 or more.
Size and shape drive the premium. HomeGuide’s size table shows the unit price rising from $250 to $1,300 at 30 by 30 inches to $500 to $1,600 at 46 by 46 inches, before any shape work. Shape complexity stacks on top, because a circle, pyramid or polygon is drawn and fabricated per order instead of pulled from stock.
| Route | Example | Typical price | Source |
|---|---|---|---|
| Standard fixed skylight (reference) | Stock fixed unit | $150 to $800 unit; $1,500 to $4,000 installed | HomeGuide, Aug 2025 |
| VELUX fixed or venting | FS, FCM, VS, VCM | $150 to $2,000 unit; $1,350 to $5,400 installed | HomeGuide, Aug 2025 |
| Custom size, curb mounted | VELUX FCM custom | Dealer quote by make size | VELUX dealers |
| Extra-large round | 60 to 90 in wide | $1,200 to $5,800 each installed | HomeGuide, Aug 2025 |
| Continuous vaulted | 16 to 84 in wide | $125 to $500 per linear foot installed | HomeGuide, Aug 2025 |
| Glass roof canopy, custom-built | 150 to 300 sq ft or larger | $3,000 to $7,000+ each | HomeGuide, Aug 2025 |
| Structural / walkable / large span | Floor light, roof deck glass | Per project only | Specialty glazing firms |
Curb, shaft and flashing work move the total as much as the glass. HomeGuide puts skylight labor alone at $1,200 to $3,200, and a skylight through an attic, which needs a framed and drywalled shaft, at $2,600 to $5,700 installed. For standard unit pricing to anchor against, see our skylight installation cost breakdown and the full skylight cost guide before you request a custom quote.
Does VELUX make custom size skylights?
Yes. VELUX builds custom size skylights through its FCM (Fixed Curb Mounted) model. Per the VELUX FCM technical data sheet, custom make sizes run from 18-3/4 inches to 50-3/4 inches in width and from 18-3/4 inches to 76-1/2 inches in length. For longer openings, VELUX Large Span skylights span up to 10 feet in length. Custom sizes are made to order, not stocked.
To get a custom size, you (or your contractor) contact VELUX or a VELUX dealer with the exact curb dimensions rather than picking a stock size code; US Building Products asks for maximum skylight clearance in 1/4-inch increments. VELUX customer service is at 1-800-888-3589. Because the FCM is curb mounted, it sits on a site built curb, which is what lets the size be flexible in the first place. For the standard model lineup and size codes, our VELUX skylights guide decodes the whole system.
| VELUX FCM spec | Value | Source |
|---|---|---|
| Laminated Low E366 glazing | U-factor 0.48, SHGC 0.27, VT 0.63 | VELUX FCM data sheet V5074-0921 |
| Tempered Low E366 glazing | U-factor 0.45, SHGC 0.28, VT 0.63 | VELUX FCM data sheet |
| Impact glazing (hurricane areas) | 2.3 mm laminated, 2.28 mm interlayer; U-factor 0.46, SHGC 0.27 | VELUX FCM data sheet |
| Skylight warranty | 10 years from purchase | VELUX FCM data sheet |
| No Leak installation warranty | 10 years, with VELUX flashings and the included adhesive underlayment | VELUX FCM data sheet |
| Glass seal warranty | 20 years | VELUX FCM data sheet |
| Hail warranty | 10 years, laminated panes only | VELUX FCM data sheet |
| Flashing range | ECL: roofing up to 1/2 in thick, 10 to 60 degree pitch; ECW: tile over 3/4 in, 14 to 60 degrees; under 10 degrees, flashing by others | VELUX FCM data sheet |
The specialty manufacturer route (shapes and structural glass)
When you need a shape VELUX does not offer, or a rectangle past the FCM’s 50-3/4 by 76-1/2 inch custom limit, you move to a fully made to order unit from a specialty skylight manufacturer. These firms build circles, octagons, pyramids, ridge lights, and structural glass to a drawing, then ship a unit engineered for your exact curb and load. For whole-roof glazing rather than a single unit, see our guide to glass roof systems.
- Marco Skylights builds custom units including tandem skylights, polygons, circles, and pyramids, all made to size, and describes itself as a Women’s Business Enterprise of over 50 years.
- Glazing Vision handles bespoke systems: its Flushglaze range includes circular, walk-on and eaves rooflights, alongside sliding-over-fixed rooflights.
- CrystaLite lists NFRC-rated, AAMA-certified glass and dome skylights plus custom sloped glazing.
- Solar Innovations builds single-slope skylights for any roof pitch and nearly any size, plus pyramid skylights shaped for snow run-off.
The tradeoff is cost and lead time. A bespoke shape or structural unit is engineered per project, so you get a quote rather than a catalog price. Lead times run from 1 to 2 weeks for a custom acrylic dome at OC Skylights to several weeks for drawn and fabricated glass.
Why custom skylights are almost always curb mounted
Nearly every custom skylight is curb mounted, not deck mounted, because the curb is what makes a non standard size possible. A curb is a raised frame built on the roof deck to the exact opening you need. On a roof flatter than 3:12, IRC R308.6.8 requires a unit skylight curb at least 4 inches above the roof plane unless the maker’s instructions say otherwise, so the unit size is set by carpentry on site rather than by a fixed factory flange.
Deck mounted (flush) skylights ship with an integrated frame sized to stock openings, which is why they do not offer the same custom flexibility. The curb also raises the glass above the roof plane, which improves drainage on lower slopes; VELUX’s ECL curb flashing is rated for 10 to 60 degree pitches, and below 10 degrees the flashing is supplied by others. That flashing detail is also the most common leak point on any skylight, so if a custom unit ever weeps, start with our skylight leak diagnosis guide. If the roof is coming off anyway, see replacing skylights when reroofing.
Lead times and how to order a custom skylight
Custom skylights are made to order, so plan for a wait. OC Skylights’ guide gives a 4 to 5 week lead time for VELUX custom sizes that are not stocked. Bespoke shapes and structural glass from specialty manufacturers can take longer because each unit is fabricated to a drawing. The order sequence:
- Measure the curb or rough opening. Get the exact width and length at the roof, not the room below, to the nearest 1/4 inch. Custom pricing is driven by these numbers.
- Decide size vs shape. If a rectangle between 18-3/4 and 50-3/4 inches wide and up to 76-1/2 inches long works, price a VELUX FCM custom size first. Move to a bespoke shape only if the design requires it.
- Request a quote. For VELUX, call 1-800-888-3589 or a dealer with dimensions. For shapes, send a drawing to a specialty manufacturer.
- Confirm the curb detail. Verify curb height (4 inches minimum under 3:12 per IRC R308.6.8), glass package, and the flashing kit for your slope and roof material.
- Order and schedule. Place the order 4 to 6 weeks ahead of install so the unit arrives before your crew frames the curb.
When a custom skylight is worth it (and when a standard one wins)
A custom skylight is worth the premium when no stock size fits the opening, when the architecture calls for a shape no manufacturer stocks, or when you need structural or walkable glass. In most homes a standard size does the job: HomeGuide’s standard-size table runs from 21 by 38 inches to 46 by 46 inches at $200 to $1,600 for the unit. Check the VELUX skylight size chart first to see whether a stock code fits.
- Go custom size when your opening falls between two stock FCM codes, or you want a slightly larger daylight area than any code offers.
- Go custom shape when the roofline, atrium, or design demands a circle, pyramid, or polygon.
- Stay standard when a catalog size fits within an inch or two. Reframing the opening to a stock size is often cheaper than a custom unit.
Glass package matters as much as size for comfort and energy bills: on the FCM alone, SHGC runs from 0.18 with Low E340 glazing to 0.28 with tempered Low E366, per the VELUX data sheet. Our energy efficient skylights guide covers the glazing and coatings worth specifying on a custom order. If you are weighing a cheaper dome, see our comparison of plastic skylights versus glass.
Frequently asked questions
Does VELUX make custom sized skylights?
Yes. VELUX makes custom size skylights through its FCM (Fixed Curb Mounted) model. Per the VELUX FCM technical data sheet, custom make sizes run from 18-3/4 to 50-3/4 inches wide and 18-3/4 to 76-1/2 inches long. For longer openings, VELUX Large Span skylights reach up to 10 feet. Custom units are made to order, so you request a quote from VELUX at 1-800-888-3589 or a dealer rather than picking a stock size code.
How much do custom skylights cost?
HomeGuide (August 2025) puts a standard fixed skylight at $150 to $800 for the unit and $1,500 to $4,000 installed, and VELUX fixed or venting models at $1,350 to $5,400 installed. A VELUX FCM custom size is quoted by dealers. Larger and shaped glazing costs more: HomeGuide lists extra-large round units at $1,200 to $5,800 each and custom-built glass roof canopies at $3,000 to $7,000 or more.
What are standard skylight sizes?
VELUX’s 2021 FCM data sheet lists 14 standard codes, from 1430 (14-1/2 by 30-1/2 inches inside curb) to 4672 (46-1/2 by 72-1/2 inches), including 2222, 2246, 3030 and 4646; VELUX’s current pro product page also lists codes such as 3422, so confirm against the live size list. HomeGuide’s general size table runs from 21 by 38 inches to 46 by 46 inches. Anything between stock codes needs a custom size or a reframed curb.
What is the difference between a custom size and a custom shape skylight?
A custom size skylight is a standard product (usually a curb mounted VELUX FCM) built to a non catalog width and length, within 18-3/4 to 50-3/4 by 76-1/2 inches for the FCM. A custom shape skylight is a made to order unit in a non rectangular form (circle, pyramid, octagon, trapezoid) from a specialty manufacturer such as Marco Skylights or Solar Innovations. Custom size is the cheaper, faster route; custom shape is engineered and quoted per project.
Do custom skylights have to be curb mounted?
Almost always, yes. The curb is a site built frame matched to your exact opening, which is what allows a non standard size. Deck mounted (flush) skylights use a factory frame sized to stock openings. On roofs flatter than 3:12, IRC R308.6.8 requires a curb at least 4 inches above the roof plane unless the manufacturer’s instructions specify otherwise.
How long do custom skylights take to make?
OC Skylights, a VELUX dealer, gives a 4 to 5 week lead time for VELUX custom sizes that are not stocked, and 1 to 2 weeks for custom acrylic domes. Bespoke shapes and structural glass from specialty manufacturers can take longer, since each unit is fabricated to a project drawing. Order 4 to 6 weeks before install so the unit arrives before your crew frames the curb.
Can you get a round or pyramid skylight?
Yes, through specialty manufacturers rather than the standard VELUX catalog. Marco Skylights builds circles, polygons, and pyramids to size, Solar Innovations builds pyramid and single-slope units, and Glazing Vision builds circular, walk-on and sliding rooflights. HomeGuide lists extra-large round units 60 to 90 inches wide at $1,200 to $5,800 each installed.
Before specifying a custom unit, see how the major manufacturers stack up in our roundup of the best skylight brands.