CONVENTIONAL ROOF CURB TERMS

ROOF CURB: A product manufactured to provide both a  watertight opening thru a buildings roof and support for the mounting of fans, ventilation equipment.Roof curbs also provide openings for duct / pipe penetrations and allow for easy access to roof mounted equipment.

CANTED STYLE: This style roof curb has a built in “cant” measuring 3” x 3” x 3” around the bottom curb perimeter and is ideal for use on flat roofs utilizing composite type rolled roofing. This “cant” allows for the easy transitioning of the roofing up the sides of the roof curb to the wood nailer without breaking or cracking the roofing materials. This style is not recommended for use on pitched or shingled roofs without first adding extended flanges.

 SELF-FLASHING STYLE: This style roof curb has straight vertical sides and is a great all-purpose curb. A “self-flashing” style roof curb is designed specifically for use on rubber roofs but with the addition of fiber cants (supplied by the roofer) they can also be used with composite rolled roofing materials. This style can be used on either flat or pitched roofs but extended flanges are recommended for use with shingled roofs.

 RAISED CANT STYLE: This style roof curb also has a built-in 3”x 3”x 3” “ cant” but as the name implies it is raised up from the bottom perimeter. This style is designed specifically for use on insulated roofs and the “raised” portion of the cant can be made to same thickness as the roofing insulation with the standard being 1-½ inches.

 WOOD NAILER: The standard wood nailers consist of a square 1-5/8” thick wood frame attached on the top of the roof curb O. D. and is provided primarily as termination point for fastening the roof materials. It also provides some dampening effect on transmitted vibrations and noise created by the fans or equipment.

 TREATED WOOD NAILER: This wood has been chemically treated to resist water and insects to help prevent rot or deterioration. Other than being chemically treated, it has the same features and functions as a standard wood nailer.

 INSULATION: Standard fiberglass insulation consist of a 1 ½” thick, 3 pound density, fibrous glass type material bonded together into a rigid form with a phenolic resin. This insulation provides a thermal barrier to help prevent condensation and also has some slight sound absorption qualities.

DAMPER SHELF OR TRAY: Standard damper shelves or trays measure 1” wide and are located on the inside bottom portion of the curb to provide support for dampers. The desired damper opening size is designated as “ E x F” which is the actual clear opening size desired and not the actual size of the damper. Damper shelves or trays need to be sized a minimum of 1” over all smaller than the actual damper size. Example: A damper with an actual O.D. size of 20” x 20” would require a minimum “E x F” size of 19” x 19”.

 SOUND BAFFLES:  Standard sound baffles consist of a series of vertically mounted 6” high baffles spaced on 5” centers constructed of 1 ½” thick 3 lb. density rigid fiberglass insulation mounted in an 18 ga. (.050) galvanized frame. They are installed from the top of the curb and screwed or riveted to curb top with the mounting flanges that are provided. Sound baffles are normally used where some measure of sound reduction is required from the curb-mounted equipment or fan.

CURB EXTENSION: Standard curb extensions are used primary to extend the height of an existing roof curb. Curb extensions also make it possible to add vents, access panels, damper shelves, hinged tops and sound baffles to existing roof curbs without having to replace the existing roof curb.

BURGLAR BARS: Standard burglar bars are manufactured using cold rolled steel bars and angle stock. The bars are ½” diameter spaced on either 6” or 8” centers in both directions. The bars are welded into a 1” x 1” angle frame and at each junction where the bars intersect. Burglar bars are usually attached to bottoms of the roof curbs with welds but can be made to fit inside of duct or wall openings.  These are classed as “BURGLAR BARS” and not “Security Bars”. Security bars are usually manufactured using high resistant tool steel, which is not available.

 ROOF CURB ADAPTERS: Roof curb adapters allow the use of an existing roof curb when replacing an existing fan or other roof mounted equipment that requires a larger or small roof curb o.d. size. Our model RCA-I is used to increase the existing roof curb o.d. to a larger roof curb o.d. The model RCA-D is used when it is necessary to reduce the existing roof curb o.d. size.

 HINGED TOP ADAPTERS: Standard hinged top adapters allow the fan or equipment to be tilted back for cleaning or adjustment. The hinged top adapter is mounted on top of a new or existing roof curb and consist of all 14 ga. steel construction, gasketing, galvanized steel butt hinges, lockable galvanized steel hasp and limit opening chains. There are weight and size restrictions on these adapters.

 ACCESS PANEL:  Standard access panel is constructed of same gauge and material as curb or curb extension and has a maximum opening width of 3” less than the curb / extension side where it’s located and is 4” less than the curb / extension height. The access panel is secured with sheet metal screws for easy removable and is sealed with a closed cell neoprene gasket. Access panel is insulated with 1 ½” 3 lb. density fiberglass insulation to match curb / extension and is omitted on non-insulated models.

 KNOCKED DOWN CONSTRUCTION: Some larger roof curbs can exceed the normal shipping size restrictions and have to be constructed in multi-sections or completely knocked down in order to fit into a truck trailer. When this type of construction is required the curb is made in as few sections as possible and assembly instructions / splice kits are included with the curb. Normally, anytime dimensions exceed 88” multi-sections or knockdown construction should be expected.

 SINGLE PITCH: Single pitched roof curbs are pitched only on one side and are used to keep the fan or equipment level when the roof is pitched to allow for water run off. Roof curbs can be pitched from 1/8” in 12” to as much as 17” in 12” with the pitch being described as the amount of pitch in 12”. When used with shingled roofing a minimum 6” extended bottom flange is recommended.

 DOUBLE PITCH: Double pitched roof curbs are pitched in two and usually opposite directions. The term “Ridge or Peaked” mounted roof curbs is occasionally used to describe these type curbs. Double-pitched roof curbs are available in the same pitches and other accessories as single pitched roof curbs.

 VENTED ROOF CURB: Vented curbs are usually associated with restaurant hood ventilation requirements such as NFPA 96 A. Usually vented roof curbs have no insulation, no wood nailer, and a special height to obtain a discharge height of 40” minimum and can be vented in either 2 opposite sides or on all 4 sides. Check the local building codes to see what will meet the local code requirements.

 COUNTER FLASHING TOP: Depending on the curb o.d. size and use, counter flashing tops can be as simple as an 18 ga. galvanized sheet metal temporary cover. With the addition of ¾” thick plywood decking and cross bracing the curb can be used as load bearing equipment platform roof curb. Curbs with counter flashing tops, which are subject to being walked on, require the plywood decking for safety. The plywood is attached directly to the top of the wood nailer on the curb.