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What Size VELUX Skylight Do You Need?

Writer: Craig Gouker Roofing
Craig Gouker Roofing
11 minutes ago
6 min read

VELUX deck-mounted skylights come in standard sizes identified by a letter and number code, from a narrow A06 (15 1/4 by 46 1/4 inches outside frame) to a wide S06 (44 3/4 by 46 1/4 inches). The right size depends on the space between your roof framing, the room below and whether you are replacing an existing skylight, in which case the product ID plate on the old unit tells you exactly what fits. For most homes, the choice starts with three widths: C (21 1/2 inches), M (30 9/16 inches) and S (44 3/4 inches).

 

The codes are easier to read than they look. In VELUX's size chart for its Fixed Skylight (FS), every code that shares a letter shares a width, and every code that shares a number shares a height: C01, C04, C06, C08 and C12 are all 21 1/2 inches wide, while A06, C06, D06, M06 and S06 are all 46 1/4 inches tall. Curb-mounted VELUX skylights use a different system, a four-digit code that matches the inside curb size, so a 2246 fits a curb that measures 22 1/2 by 46 1/2 inches inside. This guide lays out the full deck-mounted size chart, explains how to find the size of a skylight you already have, and covers the other decisions that go with choosing a size.


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What Is the Difference Between Deck-Mounted and Curb-Mounted Skylights?

 

A deck-mounted skylight attaches directly to the roof deck and is sealed with a flashing kit that works with the surrounding shingles. A curb-mounted skylight sits on a raised frame, called a curb, that is built on the roof first, and the skylight fits over the curb.

 

VELUX sizes the two types differently:

 

  • Deck-mounted skylights use letter and number codes such as C01, M04 or S06, and VELUX lists an outside frame size and a rough opening size for each.

  • Curb-mounted skylights use four-digit codes such as 2222, 2246 or 3030, and VELUX lists the inside curb, outside curb and maximum skylight clearance for each.

 

If you are replacing a skylight, start by identifying which type you have, because the two use different code systems and switching types means reworking the roof opening.

 

What Are the Standard VELUX Deck-Mounted Skylight Sizes?

 

Here are the sizes VELUX lists for its Fixed Skylight (FS), shown as outside frame, then rough opening, in inches (width by height):

 

  • A06: 15 1/4 x 46 1/4; rough opening 14 1/2 x 45 3/4

  • C01: 21 1/2 x 27 3/8; rough opening 21 x 26 7/8

  • C04: 21 1/2 x 38 3/8; rough opening 21 x 37 7/8

  • C06: 21 1/2 x 46 1/4; rough opening 21 x 45 3/4

  • C08: 21 1/2 x 54 15/16; rough opening 21 x 54 7/16

  • C12: 21 1/2 x 70 3/4; rough opening 21 x 70 1/4

  • D26: 23 1/4 x 23 7/16; rough opening 22 1/2 x 22 15/16

  • D06: 23 1/4 x 46 1/4; rough opening 22 1/2 x 45 3/4

  • M02: 30 9/16 x 30 1/2; rough opening 30 1/16 x 30

  • M04: 30 9/16 x 38 3/8; rough opening 30 1/16 x 37 7/8

  • M06: 30 9/16 x 46 1/4; rough opening 30 1/16 x 45 3/4

  • M08: 30 9/16 x 54 15/16; rough opening 30 1/16 x 54 7/16

  • S01: 44 3/4 x 27 3/8; rough opening 44 1/4 x 26 7/8

  • S06: 44 3/4 x 46 1/4; rough opening 44 1/4 x 45 3/4

 

The rough opening is the framed hole in the roof deck, and the outside frame is the size of the skylight itself. Always plan the framing around the rough opening number.

 

Do Venting Skylights Come in the Same Sizes?

 

Mostly, yes. VELUX's Solar Powered Fresh Air (VSS) and Manual Fresh Air (VS) deck-mounted skylights share the C01 through S06 codes and dimensions used by the fixed skylight, including M02. The Electric Fresh Air (VSE) chart lists the same codes except M02. The fixed skylight is the only one of these that adds the narrow A06, the long C12 and the D26 and D06 sizes.

 

That matters if you want a fixed skylight in one spot and a venting unit in another. Matching codes let the two look consistent from inside the room. If you are weighing a motorized model, our article on whether electric skylights are worth the extra installation cost covers the tradeoffs.

 

How Do You Find the Size of Your Existing Skylight?

 

If you are replacing a VELUX skylight, the product ID is the fastest way to confirm the size. According to VELUX:

 

1. On a deck-mounted fixed skylight, the product ID plate is on the bottom left of the frame.

 

2. On deck-mounted solar or electric Fresh Air skylights, the plate is on the bottom left of the sash.

 

3. On curb-mounted skylights, the product ID information is stamped into the side of the exterior covers.

 

4. On newer systems installed after April 2025, VELUX says a QR code on the included remote control holds the identifying information.

 

VELUX says the product ID includes the skylight model, glass type and date of manufacture, and you will need it to order shades or have the skylight serviced. If there is no readable plate, your roofer can measure the rough opening from the attic side. Our guide on when to schedule a skylight replacement covers the signs that an older unit is due.

 

What Else Should You Consider When Choosing a Skylight Size?

 

Size is only one part of the decision. Before you settle on a code, think through:

 

  • Roof framing: Wider sizes such as M and S may require reframing between roof rafters, which your installer confirms from the attic.

  • Room size and use: A C01 over a small bathroom and an S06 over a family room create very different amounts of light.

  • Ceiling shaft: On homes with an attic, the light shaft from the roof to the ceiling affects how much of the skylight you see from below.

  • Roof pitch: VELUX lists its step flashing for asphalt shingles, wood shakes or slate on roofs from 14 to 85 degrees.

  • Shades: VELUX says you need the product ID to order shades and other accessories, so keep it with your home records.

 

For a broader planning checklist, see what to know before adding a skylight.

 

Which Flashing Kit Goes With a VELUX Deck-Mounted Skylight?

 

VELUX pairs each deck-mounted skylight with a flashing kit that matches the roofing material. For its Fixed Skylight, VELUX lists:

 

  • EDL step flashing with adhesive underlayment for asphalt shingles, wood shakes or slate, for roof pitches from 14 to 85 degrees

  • EDW high profile flashing for tile roofs

  • EDM metal roof flashing for metal roofs

 

The flashing is what ties the skylight into the roof, so the kit has to match both the skylight size and the roofing material. Our article on why skylights sometimes leak over time explains what to watch for.

 

FAQ

 

What does a VELUX size code like C06 mean?

 

In VELUX's deck-mounted charts, the letter sets the width and the number sets the height. A C06 fixed skylight is 21 1/2 by 46 1/4 inches outside frame, with a 21 by 45 3/4 inch rough opening.

 

What does a four-digit VELUX code like 2246 mean?

 

Four-digit codes are for curb-mounted skylights and match the inside curb size. A 2246 fits a curb measuring 22 1/2 by 46 1/2 inches inside.

 

Where is the size on my VELUX skylight?

 

Look for the product ID plate on the bottom left of the frame on a fixed deck-mounted skylight, or the bottom left of the sash on a Fresh Air model. Curb-mounted units have the information stamped into the side of the exterior covers.

 

Can I replace my skylight with a different size?

 

Yes, but a size change means reframing the roof opening and finishing the interior shaft to match, which adds work. Replacing with the same code is simpler.

 

What sizes do VELUX Sun Tunnels come in?

 

VELUX lists its Low Profile rigid Sun Tunnel in 10, 14 and 22 inch diameters.

 

Is the best time to change skylight size during a roof replacement?

 

It is often the most practical time, because the roof deck is exposed and the new flashing can be integrated with new underlayment and shingles.

 

Why Pittsburgh Homeowners Choose Craig Gouker Roofing for VELUX Skylights

 

Craig Gouker Roofing has been replacing roofs in the Pittsburgh area since 1991 and installs VELUX skylights, including traditional skylights, roof windows, modular skylights and sun tunnels, with several venting options and opening mechanisms. As an Owens Corning Platinum Preferred Contractor focused on full roof replacements, the company encourages homeowners to ask their estimator about adding or replacing skylights as part of a roof replacement project. Learn more on our skylight installation and replacement page and request a free estimate.

 

Visit Craig Gouker Roofing or call (412) 664-7679 today. Contact us for more information.


Craig Gouker Roofing

 
 
 

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