AES Roof Curbs: How to Read ARC3 and ARC6 Skylight Curb Model Numbers

AES Industries builds galvanized steel roof curbs, the raised frames that skylights and smoke vents mount on. We carry two AES skylight curb families, ARC3 and ARC6, plus the AES-3 rail curb for rooftop equipment. Every AES skylight curb model number follows one pattern, for example 4896 ARC3 12H 18GA SSG. The segments give the size, the curb family, the height, the steel gauge and the safety guard. This guide explains each segment, using only what the AES shop drawings and our product listings show.

How to read an AES skylight curb model number

The AES shop drawings carry the same pieces in their titles. The drawing for the 36120 curb, for example, reads "SKYLIGHT / ARC3 / 36120 / 12H / 18GA".

Segment	Example	What it means
Size code	4896	The nominal curb size. On most sizes it equals the inside dimension in inches (4896 is 48 x 96 inches inside). Some sizes are exceptions, listed below
Curb family	ARC3 or ARC6	ARC3 curbs are insulated at the factory. ARC6 curbs are not insulated. See the comparison below
Height	9H, 12H, 14H, 16H	Curb height in inches
Gauge	14GA or 18GA	Galvanized steel gauge
Guard	SSG, CG or NG	SSG: 3/16 inch security grid at 6 inches on center. CG: 3/16 inch security grid at 4 x 4 inches on center. NG: no guard

The AES documents we have do not say what the letters ARC, SSG or CG stand for, so we describe each code by what the drawings show rather than by an expanded name.

ARC3 vs ARC6

	ARC3	ARC6
Insulation	1-1/2 inch thick, 3 pound density fiberglass behind 20 gauge liners	None (non-insulated)
Nailer	2 x 2	2 x 4 pressure treated
Guard on the models we list	SSG grid, welded to the frame 2.5 inches below the curb top	CG grid or NG (no guard)
Outside dimension on our listings	Inside dimension plus 3 inches each way	Inside dimension plus 3.5 inches each way
Steel	18 gauge, or 14 gauge on the 4040	18 gauge, or 14 gauge on the 5060 and one 4848

Both families have full height mitered and welded corners and a pre-primed white interior. On the ARC3, the security grid is also painted white.

Pick the ARC3 when you want the curb insulated at the factory. Pick the ARC6 when the roofer will insulate the curb in the field. Whichever family you choose, the outside dimension is what the skylight or smoke vent frame must fit, so check it against the unit's cut sheet.

Every AES skylight curb we list

Model	Inside (in)	Outside (in)	Nominal
36120 ARC3 12H 18GA SSG	36 x 120	39 x 123	3 x 10 ft
4040 ARC3 12H 14GA SSG	47 x 47	50 x 50	4 x 4 ft
4896 ARC3 9H, 12H and 16H 18GA SSG	48 x 96	51 x 99	4 x 8 ft
4848 ARC6 12H 14GA CG and 14H 18GA CG	48 x 48	51.5 x 51.5	4 x 4 ft
4872 ARC6 14H 18GA NG	48 x 72	51.5 x 75.5	4 x 6 ft
4896 ARC6 14H 18GA CG and NG	48 x 96	51.5 x 99.5	4 x 8 ft
4896 ARC6 14H 18GA CG - VLX SVT	47.5 x 95.5	51 x 99	4 x 8 ft
5060 ARC6 14H 14GA CG	58.875 x 70.875	62.375 x 74.375	5 x 6 ft
6060 ARC6 14H 18GA NG	60 x 60	Confirm on the drawing	5 x 5 ft

The exceptions that catch people

• 4040 is a 4 x 4 foot curb that measures 47 x 47 inches inside, not 40 x 40.
• 5060 is a 5 x 6 foot curb that measures 58.875 x 70.875 inches inside.
• 4896 ARC6 CG - VLX SVT is built for VELUX smoke vents. It has a 51 x 99 inch outside dimension, and its 4 x 4 screen is attached 1 inch below the curb top so the smoke vent mechanism has room to work.
• A 4896 ARC3 and a 4896 ARC6 have the same inside size but different outside sizes (51 x 99 vs 51.5 x 99.5), so confirm which one the skylight or vent was sized for.

Our advice: order from the inside and outside dimensions on the product page and the AES drawing, not from the size code alone.

Guards and OSHA

OSHA 1910.28(b)(3)(i) treats a skylight as a hole. Each employee must be protected from falling through a skylight that is 4 feet or more above a lower level by a cover, a guardrail system, a travel restraint system or a personal fall arrest system. SSG and CG curbs ship with a 3/16 inch grid installed at the factory, although the ARC drawings do not list a load rating for it. NG curbs have no guard, so plan for fall protection some other way when you order one. For more background, see OSHA fall protection for skylights.

AES-3 rail curb supports

The AES-3 is not a skylight curb. It is a self-flashing rail curb that supports rooftop equipment. Its model number reads the same way: AES-3 10H 120L 18GA is 10 inches high, 120 inches long and 18 gauge. Our listings describe each one as 18 gauge with a 2 x 4 wood nailer and a mill finish, and the AES drawing shows an 18 gauge cap over a 2 x 4 pressure treated nailer. We carry the 8H 96L, 10H 96L, 10H 120L, 12H 48L and 12H 120L.

The AES equipment support specification calls for a minimum height of 8 inches above the finished roof, a slope matching the roof slope, and a support that spans at least two structural members. No load may be applied to a cantilever longer than 1 foot. AES guarantees equipment supports against defects in material and workmanship for one year.

Installation note

The AES skylight curb installation sheet says its connection details are suggestions only. The installer is responsible for meeting local building codes and the architect's or engineer's requirements.

FAQ

Is this AES the roof curb company?

Yes. This guide covers AES Industries roof curbs for skylights and smoke vents, and its rail curbs for rooftop equipment.

Is the size in an AES model number the inside or outside of the curb?

Usually the inside, but not always. The 4040 is 47 x 47 inches inside and the 5060 is 58.875 x 70.875, so check the listed dimensions.

Which AES curb should I order to insulate in the field?

An ARC6. Our listing for the 6060 ARC6 describes it as non-insulated, to be field insulated.

Next steps

All of these curbs are on our AES Industries brand page. Curbs from every fabricator we carry are on the roof curbs page, AES drawings are on the roof curb spec sheets page, and our Curbs Plus curb guide covers the other curb line we carry. Send the quantity, model, inside and outside dimensions and the unit going on top through the curbs request for quote page, and we will confirm the configuration before AES fabricates it.