Statutes, codes, and regulations
District Of Columbia Administrative Code
Title 12 - CONSTRUCTION CODES SUPPLEMENT OF 2013Subtitle 12-B - RESIDENTIAL CODE SUPPLEMENT OF 2013
Chapter 12-B16 - DUCT SYSTEMS
Rule 12-B1601 - M1601 - DUCT CONSTRUCTION

D.C. Mun. Regs. tit. 12, r. 12-B1601

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Current through Register Vol. 72, No. 2, January 10, 2025
Rule 12-B1601 - M1601 - DUCT CONSTRUCTION

Strike Section M1601.1.1 of the International Residential Code in its entirety and insert new Section M1601.1.1 in the Residential Code in its place to read as follows:

M1601.1.1

Above-ground duct systems. Above-ground duct systems shall conform to the following:

1.Equipment connected to duct systems shall be designed to limit discharge air temperature to a maximum of 250ºF (121ºC).
2. Factory-made air ducts shall be constructed of Class 0 or Class 1 materials as designated in Table M1601.1.1(1).
3. Fibrous duct construction shall conform to the SMACNA Fibrous Glass Duct Construction Standards or NAIMA Fibrous Glass Duct Construction Standards.
4. Minimum thickness of metal duct material shall be as listed in table M1601.1.1(2). Galvanized steel shall conform to ASTM A653. Metallic ducts shall be fabricated in accordance with SMACNA HVAC Duct Construction Standards - Metal and Flexible.
5. Use of gypsum products to construct return air ducts or plenums is permitted, provided that the air temperature does not exceed 125ºF (52ºC) and exposed surfaces are not exposed to condensation.
6.Duct systems shall be constructed of materials having a flame spread index not greater than 200.
7. Stud wall cavities and the spaces between solid floor joists to be used as air plenums shall comply with the following conditions:
7.1.

These cavities or spaces shall not be used as a plenum for supply air.

7.2.

These cavities or spaces shall not be part of a required fire-resistance-rated assembly.

7.3.

Stud wall cavities shall not convey air from more than one floor level.

7.4.

Stud wall cavities and joist-stud plenums shall be isolated from adjacent concealed spaces by tight-fitting fire blocking in accordance with Section R602.8.

7.5.

Stud wall cavities in the outside walls of building envelope assemblies shall not be utilized as air plenums.

Strike Section M1601.4.1 of the International Residential Code in its entirety and insert new Section M1601.4.1 in the Residential Code in its place to read as follows:

M1601.4.1

Joints, seams and connections. All longitudinal joints, seams and connections in metallic and nonmetallic ducts shall be constructed as specified in SMACNA HVAC Duct Construction Standards - Metal and Flexible and NAIMA Fibrous Glass Duct Construction Standards. All joints, longitudinal and transverse seams, and connections in ductwork shall be securely fastened and sealed with welds, gaskets, mastics (adhesives), mastic-plus-embedded-fabric systems, liquid sealants or tapes.

Closure systems used to seal flexible air ducts and flexible air connectors shall comply with UL 181B and shall be marked "181 B-FX" for pressure-sensitive tape or "181 B-M" for mastic. Duct connections to flanges of air distribution system equipment shall be sealed and mechanically fastened. Mechanical fasteners for use with flexible non-metallic air ducts shall comply with UL 181B and shall be marked "181 B-C." Crimp joints for round metallic ducts shall have a contact lap of not less than 1 inch (25.4 mm) and shall be mechanically fastened by means of not less than three sheet-metal screws or rivets equally spaced around the joint.

Closure systems used to seal metal ductwork shall be installed in accordance with the manufacturer's instructions. Round metallic ducts shall be mechanically fastened by means of at least three sheet-metal screws or rivets spaced equally around the joint. Unlisted duct tape shall not be permitted as a sealant on any duct.

Exceptions:

1. Spray polyurethane foam shall be permitted to be applied without additional joint seals.
2. Where a duct connection is made that is partially inaccessible, three screws or rivets shall be equally spaced on the exposed portion of the joint so as to prevent a hinge effect.
3. Continuously welded and locking-type longitudinal joints and seams in ducts operating at static pressures less than 2 inches of water column (500 Pa) pressure classification shall not require additional closure systems.

D.C. Mun. Regs. tit. 12, r. 12-B1601

Final Rulemaking published at 61 DCR 3063 (March 28, 2014 - Part 2)
The District of Columbia Residential Code (2013), referred to as the "Residential Code," consists of the 2012 edition of the International Residential Code for One- and Two-Family Dwellings, published by the International Code Council (ICC), as amended by the District of Columbia Residential Code Supplement (2013) (12 DCMR B). The International Residential Code is copyrighted by the ICC and therefore is not republished here. However, a copy of the text may be obtained at:http://publicecodes.cyberregs.com/icod/irc/2012/index.htm?bu=IC-P-2012-000002&bu2=IC-P-2012-000019.
Authority: Section 10 of the Construction Codes Approval and Amendments Act of 1986 (Act), effective March 21, 1987 (D.C. Law 6-216; D.C. Official Code § 6-1409 (2012 Repl.)) and Mayor's Order 2009-22, dated February 25, 2009, as amended.