VELUX Commercial CMD2 Dynamic Dome Skylights: Sizes, Glazing Codes and Curbs

The VELUX Commercial CMD2 is a curb-mount Dynamic Dome skylight: two domes on a thermally broken aluminum frame that sits over a roof curb. A model number such as CMD2 4848 P1C2 gives the model, the size and the glazing. This guide covers each part, the glazing choices, the curb and the matching screens, using the VELUX documents posted on our product pages.

How to read a CMD2 model number

Segment	Example	What it means
Model	CMD2	Curb mounted dynamic double dome skylight with an aluminum frame
Size code	4848	Inside curb dimension in inches, width x length. 4848 is 48 x 48 inches
Glazing code	P1C2	Outer dome code (P1) followed by inner dome code (C2). Decoded below

VELUX also calls the inside curb dimension the rough opening. For 120 inch lengths the code drops the last digit, so a 3612 is 36 x 120 inches. Each skylight fits a curb 3 inches larger each way outside, so a 4848 fits a 51 x 51 inch curb. The documents we have do not explain a trailing letter such as the M in E2A1M, so match it to the cut sheet.

Every CMD2 size we list

Size code	Inside curb (in)	Outside curb (in)	Nominal	Versions we list
2448	24 x 48	27 x 51	2 x 4 ft	P1C2
3636	36 x 36	39 x 39	3 x 3 ft	P1C2, X1P2
3696	36 x 96	39 x 99	3 x 8 ft	P1C2, X1P2
3612	36 x 120	39 x 123	3 x 10 ft	P1C2
4848	48 x 48	51 x 51	4 x 4 ft	P1C2, P1P1, X1P2, E2A1M
4860	48 x 60	51 x 63	4 x 5 ft	P1C2
4872	48 x 72	51 x 75	4 x 6 ft	P1C2
4896	48 x 96	51 x 99	4 x 8 ft	P1C2, E2A1M
6060	60 x 60	63 x 63	5 x 5 ft	P1C2
6072	60 x 72	63 x 75	5 x 6 ft	P1C2
6096	60 x 96	63 x 99	5 x 8 ft	P1C2
7272	72 x 72	75 x 75	6 x 6 ft	P1P2

The VELUX CMD2 drawing lists more sizes. Two of them, the 4783 and the 5060, break the size code pattern, so ask us for the drawing.

Glazing codes: P1C2, P1P1, P1P2, X1P2 and E2A1

The first pair is the outer dome and the second is the inner dome. P1 is LuxGuard clear smooth polycarbonate (0.118 inch), P2 LuxGuard white smooth, C2 LuxGuard white prismatic, X1 LuxGuard Plus clear (0.150 inch), E2 Satin Sky infrared blocking acrylic and A1 clear acrylic.

Glazing	U-factor	SHGC	VLT	Listed on the cut sheet
P1C2	0.65	0.46	61.9%	NFRC, FM, ICC-ES ESR 4108
P1P2	0.65	0.49	66.4%	NFRC, FM
X1P2	0.65	0.46	65.6%	FM, Miami-Dade NOA 22-0412.02
E2A1M	0.65	0.37	56.8%	NFRC (no FM listed)
P1P1	Confirmed on the quote			See below

P1C2: the standard choice

Most of our CMD2 listings are P1C2. The VELUX guide specification rates it at 100 percent haze, so the white prismatic inner dome fully diffuses the light, and its Factory Mutual 4431 paragraph calls for CMD2 with P1C2 glazing. The prismatic inner dome is not offered on the 7272, which is why our 7272 is a P1P2.

P1P1 vs P1C2

The CMD2 4848 P1P1 replaces the white prismatic inner dome with a second clear dome. VELUX says to use a white interior dome when 100 percent light diffusion is required, so choose P1C2 for diffused light and P1P1 when the project calls for clear glazing. Its posted drawing has no thermal values, so we confirm U-factor, SHGC and VLT on the quote.

X1P2 for hurricane zones

X1P2 pairs a 0.150 inch LuxGuard Plus clear outer dome with a white smooth inner dome. Its cut sheets list HVHZ testing at Missile Level D with plus or minus 80 psf cycle pressure, and our listings describe it as hurricane rated and Florida approved. For High Velocity Hurricane Zone and Miami-Dade projects, the VELUX guide specification limits LuxGuard Plus to 4 x 8 or 5 x 6 feet.

E2A1M EcoSky

E2A1M pairs an infrared blocking Satin Sky 2 acrylic outer dome with a clear acrylic inner dome. Its SHGC of 0.37 is the lowest of our CMD2 glazings. Acrylic domes carry a 5 year warranty rather than the 15 year polycarbonate term.

Dome, hail and warranty

The dome rises at least 30 percent of the skylight width, a shape meant to capture low morning and afternoon sun. LuxGuard and LuxGuard Plus outer domes are tested to FM 4430 severe hail with 2 inch ice balls, and VELUX warrants polycarbonate dome skylights for 15 years, including leaks and hailstones 2 inches or less. Through Logistics Lighting the Dynamic Dome is also available with a 20 year warranty; see our Johns Manville skylight program page.

Curb requirements

The CMD2 mounts on a site-built or prefabricated curb, on roof pitches from 0 to 60 degrees, with the top of the curb parallel to the finished roof slope. Order by the curb's outside dimension, which the VELUX installation instructions say to measure before the skylight goes on.

• Curbs we list that match a 4848 or 4896: the Curbs Plus CPC-3 4848 (51 x 51 outside) and CPC-3 4896, the AES 4896 ARC3 and the VELUX CCAM 4896 1220, all 51 x 99 outside. The CPC-3 and ARC3 already include a screen.
• Check with us first: the AES 4896 ARC6 measures 51.5 x 99.5 inches outside.
• VELUX curbs: CCA3 (factory insulated steel), CCA6 (steel, insulated in the field) and CCAM or CCAW (factory insulated aluminum), warranted 1 year for steel and 5 years for aluminum.

Installing on the curb

VELUX calls this a dry installation: the PVC inner frame seals to the curb without sealant or tape. Secure and square the curb, clean the top edge, center the skylight with even spacing on all sides and press it down gently. Drive a corrosion resistant screw straight in at every pre-drilled hole without overtightening, then flash the curb using standard roofing practices. VELUX fasteners come in a bag of 25.

Screens and accessories

The P1C2 cut sheets report OSHA fall protection tests to a 1,000 lbf static load and a 1,600 lbf-ft dropped load, yet VELUX warns never to sit, step or walk on a skylight and recommends fall protection.

• CAE exterior safety screen. 4 x 4 inch welded galvanized steel mesh, clamped to the outside edge of the skylight frame with VELUX clamps and fasteners. We list the CAE 4848, CAE 4896 and CAE 6060.
• CRGA ICD interior safety screen. 3/16 inch mesh at 6 inches on center on a frame that mounts to the top of the curb. We list the CRGA 4872 and CRGA 4896.
• CAV ventilation curb extension. The CAV 4896 0000AR is a louvered extension with a rain defender that fits between a 48 x 96 curb and the skylight.

VELUX rates both screens for a minimum static load of 400 pounds per square foot. For background, see OSHA fall protection for skylights.

FAQ

What does P1C2 mean on a VELUX skylight?

A LuxGuard clear smooth polycarbonate outer dome (P1) over a LuxGuard white prismatic polycarbonate inner dome (C2).

Is 4848 the skylight size or the curb size?

The inside curb dimension, 48 x 48 inches. The skylight fits a curb that is 51 x 51 inches outside.

Will a CMD2 fit my existing curb?

Compare its outside dimension with the size table. If it does not match, send us measurements and a photo.

Next steps

Every VELUX product we carry is on our VELUX brand page, cut sheets are on the skylight specification sheets page, and our Curbs Plus and AES guides cover the curbs. Send the quantity, size code, glazing code, curb outside dimension and screen choice through the skylight request for quote page, and we will confirm the configuration before it is built.