1.01 Scope
A. Work covered by this specification consists of furnishing all labor, equipment, materials and accessories, and performing all operations required, for correct fabrication and installation of air duct systems using fibrous glass duct board, in accordance with applicable project drawings and specifications, subject to terms and conditions of the contract:
B. The finished duct system shall meet the requirements of NFPA 90A and 90B by complying with the requirements of Underwriters Laboratories Standard for Safety UL 181 for Class 1 Air Duct.
C. Dimensions shown on the plans are finished inside dimensions. Fabrication and installation shall conform to the manufacturer's recommendations and to the requirements of the latest edition of the North American Insulation Manufacturers Association's Fibrous Glass Duct Construction Standard (hereinafter referred to as NAIMA FGDCS).
D. Grooves and shiplaps shall be made using specific tools and/or machines designed for that purpose. Ends shall meet so that shiplaps fit without ridges or rough edges.
1.02 Delivery and storage of materials
A. All materials and/or fabricated duct sections and fittings shall be delivered to the job site in good condition and stored in a safe dry place.
B. All means necessary shall be used at the job site to protect materials from dust, dirt, moisture, and physical abuse before and during installation.
2.01 Insulated duct system
A. All rectangular supply ducts, return ducts, and related fittings of 96 in. (2400mm) span or less operating at + 2 in. w.g. (+ 500 Pa) shall be fabricated from one of the following:
B. Duct board shall be imprinted with the manufacturer's name, board type, and R-value in a repeat pattern. Additionally, each full duct board sheet shall have a UL Class 1 Air Duct label adhered to the facing of the board. Flexible ducts shall be identified in a similar manner.
C. The duct board shall have an air barrier/vapor retarder facing of aluminum foil/kraft laminate reinforced with scrim.
2.02 Alternate material specification
A. Lined or coated duct board products are available for use where it is desired to have the airstream surface coated or faced to (1) isolate the glass fiber substrate, (2) inhibit penetration of the insulation by dust, dirt or other pollutants, and (3) provide a surface that is easily cleanable. These products may be rated for internal air velocities exceeding 2,400 fpm (12 m/s).
2.03 Closure materials
Closure materials shall be one of the following:
A. Pressure-sensitive aluminum foil tapes listed and labeled under UL 181A, Part I (P), identified by name, date of manufacture, product name/number, and UL 181A-P. Minimum width of pressure-sensitive tape for 1 in. (25mm) duct board is 21/2 in. (64mm). 3 in. (76mm) pressure-sensitive tape is recommended for 11/2 in. (38mm) duct board and required for 2 in. (51mm) duct board.
B. Heat-activated tapes listed and labeled under UL 181A, Part II (H), identified by name, date of manufacture, product name/ number, and UL 181A-H, may be used in all applications except for bonding to sheet metal. Tapes shall be at least 3 in. (76mm) wide.
C. Mastic as listed under UL181A, Part III (M) and applied in conjunction with 3 in. (76mm) wide glass fabric tape. This closure system may be used as an alternative to either pressure-sensitive or heat-activated tapes for all closure applications, and must be used to bond duct board to sheet metal when system operating pressure is greater than 1 in. w.g. (125 Pa). It may also be required in some fire-rated assemblies.
3.01 Receiving Inspection
A. All materials shall be inspected to verify that the duct system may be installed in accordance with project drawings, operating performance parameters, limitations, and standards published in NAIMA FGDCS.
3.02 Fabrication, straight duct and fittings
A. All straight duct sections shall be fabricated in accordance with NAIMA FGDCS, Section II, and all fittings shall be fabricated in accordance with NAIMA FGDCS, Section III, using proper machinery, tools, and techniques.
3.03 Closure
A. Mechanical fasteners of the types shown in NAIMA FGDCS, Section IV, shall be used to connect the duct board to sheet metal before application of closure material.
B. Flaps on all field joints shall be stapled approximately 2 in. (50mm) on centers with 1/2 in. (13mm) (min.) outward clinching steel staples near the edge of the flap. On fitting joints where stapling flaps cannot be included as part of the construction, tape tabs 8 in. (200mm) (min.) in length shall be applied. Tape tabs shall be centered over the joint, a minimum of one tab per duct side and/or 12 in. (300mm) (max.) on centers.
C. On field joints, all taping surfaces shall be wiped clean before sealing. If the surface is contaminated with grease or oil, it shall be cleaned with a solvent recommended by the tape manufacturer.
D. Pressure-sensitive tape shall be firmly rubbed in place immediately after application using a squeegee tool. When the duct surface temperature is below 50˚F (10˚C), a heat-sealing tool shall be used to assure bonding. Pressure-sensitive tapes may be used to seal to properly cleaned sheet metal when system operating pressure is less than 1 in. w.g. (125 Pa).
E. Heat-activated tape closures shall be sealed with an iron (a heat gun may not be used) using a smearing action. Heat-sealing equipment must be capable of maintaining a sufficient temperature at the duct surface to assure an adequate bond. Colored dots on tape surface shall become darkened, indicating that satisfactory bonding temperature has been reached. Staples may be omitted when closures are made by machine using heat-activated tape. Joint shall be allowed to cool before stressing.
F. Mastic shall be brushed onto joint and glass fabric embedded in it. A second coat of mastic shall be brushed over the glass fabric until the fabric is filled. Mastic shall be applied in accordance with application instructions on the container, and allowed to cure before stressing.
3.04 Reinforcement
A. All straight ducts and fittings shall be reinforced to prevent ballooning, collapsing, or sagging using either the formed sheet metal system or the tie rod system in accordance with the provisions of Section V of NAIMA FGDCS. Tie rod washers shall be 21/2 in. (64mm) square or 3 in. (76mm) diameter and shall be made of plated or galvanized sheet metal of at least 0.028 in. (0.7mm) thickness, with turned edges to prevent cutting into the facing of the duct board. Hole size shall be approximately 0.150 in. (4mm) to allow the tie rod to move freely through the washer.
B. To prevent sagging of top panels of supply ducts over 48 in. (1200mm) wide reinforced with formed sheet metal channel, #10 plated sheet metal screws with 21/2 in. (64mm) square or 3 in. (76mm) diameter galvanized steel washers shall be installed inside the duct on the longitudinal centerline of the duct. When tie rod reinforcement is used, sag support shall consist of 1/2 in. (13mm) rigid galvanized steel conduit and 21/2 in. (64mm) square or 3 in. (76mm) diameter galvanized steel washers inside the duct on the longitudinal centerline 3 in. (76mm) from the male shiplap edge. For all negative pressure systems, refer to NAIMA FGDCS for proper spacing of reinforcement and proper attachment to the duct board.
3.05 Hanging and support
A. The duct system shall be supported in accordance with the provisions of Section VI of NAIMA FGDCS.
B. All hangers, supports, and attachments to the structure must be capable of withstanding three times the anticipated load.
3.06 Accessories
A. Doors, coils, dampers, registers, grilles, diffusers, air turning vanes, air volume extractors, and other accessory items shall be installed as detailed in NAIMA FGDCS with adequate reinforcement and support to accommodate additional weight without damage to the duct board.
Dampers over 2 square feet (0.19m2) shall be supported by sheet metal sleeves with all moving parts shielded with galvanized sheet metal at abrasion points. All 90˚ elbows shall contain turning vanes spaced at 3 in. (75mm) (max.) intervals, mounted in accordance with the turning vane manufacturer's instructions. Turning vanes shall not be considered as reinforcing members. If air volume extractors or splitter dampers are required on side take-off and split duct connections, these shall be fabricated using appropriate hardware. Slip-in electric heating coils shall be supported independently of the duct system and installed in galvanized sheet metal sleeves extending 6 in. (150mm) (min.) on both sides of the coils.
Accessory items shall be connected to the duct system using 21/2 in. (64mm) square or 3 in. (76mm) round galvanized or plated steel washers and #10 sheet metal screws of appropriate length to spread the load to the duct board.
3.07 Final Inspection
A. Upon completion of installation of the duct system and before operation is to commence, the system shall be visually inspected to verify that it has been correctly installed using the Inspection Check List in NAIMA FGDCS. Any scraps and loose pieces of material shall be removed from inside the duct system.
B. All dampers shall be opened and fans turned on to blow all remaining loose material out of the duct system.
C. The duct system shall be checked to ensure that there are no air leaks through joints or through tears or punctures of the air barrier facing. If tears or punctures are found, these shall be repaired using procedures as detailed in Section VIII, NAIMA FGDCS.
3.08 Safety precautions
A. All job site operations shall be conducted in compliance with applicable provisions of the Occupational Safety and Health Act, NAIMA's Health and Safety Partnership Program (HSPP) and all state and/or local safety and health codes and regulations that may apply to the work. Manufacturer's Material Safety Data Sheets (MSDS) shall be consulted when appropriate.