Oklahoma Administrative Code
Title 748 - Oklahoma Uniform Building Code Commission
Chapter 20 - Adopted Codes
Subchapter 6 - IRC®2018
Section 748:20-6-21 - IRC[®] 2018 Chapter 16 Duct Systems

Universal Citation: OK Admin Code 748:20-6-21

Current through Vol. 42, No. 7, December 16, 2024

Chapter 16 of the 2018 IRC® is adopted with the following modifications:

(1) Table M1601.1.1 Duct construction minimum sheet metal thickness for single dwelling units has been stricken from the code and replaced with a newly created table with the same table heading. The newly created table contains three rows and three columns and a footnote. The newly created table is described below:

(A) Row 1 is the header row and contains three columns, one of which is divided into two sub-rows as described below:
(i) Row 1, column 1 header is entitled "Duct Size"

(ii) Row 1, column 2 header is entitled "Galvanized" and contains two sub-rows:
(I) Row 1, column 2, sub-column 1 header is entitled "Minimum thickness (inches)."

(II) Row 1, column 2, sub-column 2 header is entitled "Equivalent Galvanized Gage No."

(iii) Row 1, column 3 is entitled "Approximate Aluminum B and S Gage."

(B) Row 2 contains 2 sub-rows with the following information listed:
(i) Row 2, sub-row 1, column 1 contains the wording "Round ducts and enclosed rectangular ducts 14 inches or less."

(ii) Row 2, sub-row 1, column 2 contains the following numbers in each sub-column:
(I) Row 2, sub-row 1, column 2, sub-column 1 contains the number "0.013."

(II) Row 2, sub-row 1, column 2, sub-column 2 contains the number "30."

(iii) Row 2, sub-row 1, column 3, contains the number "26."

(iv) Row 2, sub-row 2, column 1 contains the wording "Round ducts and enclosed rectangular ducts over 14 inches."

(v) Row 2, sub-row 2, column 2 contains the following numbers in each sub-column:
(I) Row 2, sub-row 2, column 2, sub-column 1 contains the number"0.016."

(II) Row 2, sub-row 2, column 2, sub-column 2 contains the number "28."

(vi) Row 2, sub-row 2, column 3 contains the number "24."

(C) Row 3 contains two sub-rows with the following information listed:
(i) Row 3, sub-row 1, column 1 contains the wording "Exposed rectangular ducts 14 inches or less."

(ii) Row 3, sub-row 1, column 2 contains the following numbers in each sub-column:
(I) Row 3, sub-row 1, column 2, sub-column 1 contains the number "0.016."

(II) Row 3, sub-row 1, column 2, sub-column 2 contains the number "28."

(iii) Row 3, sub-row 1, column 3, contains the number "24."

(iv) Row 3, sub-row 2, column 1 contains the wording "Exposed rectangular ducts over 14 inches."

(v) Row 3, sub-row 2, column 2 contains the following numbers in each sub-column:
(I) Row 3, sub-row 2, column 2, sub-column 1 contains the number"0.019."

(II) Row 3, sub-row 2, column 2, sub-column 2 contains the number "26."

(vi) Row 3, sub-row 2, column 3 contains the number "22."

(D) Between the end of the table and Footnote "a" is the wording "For SI: 1 inch is equal to 25.4 mm."

(E) Footnote "a" has been added to read: "a. Ductwork that exceeds 20 inches by dimension or exceeds a pressure of 1-inch water gage (250 pa) shall be constructed in accordance with SMACNA HVAC Duct Construction Standards Metal and Flexible."

(2) Section M1601.4.1 Joints, seams, and connections. This section has been modified to add a fourth exception for duct systems with sheet metal plenums, Y's and supply boots with liquid applied sealants. This section has been modified to read: M1601.4.1 Joints, seams and connections.

(A) Longitudinal and transverse 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. Joints, longitudinal and transverse seams, and connection in ductwork shall be securely fastened and sealed with welds, gaskets, mastics (adhesive), mastic-plus- embedded-fabric systems, liquid sealants or tapes. Tapes and mastics used to seal fibrous glass ductwork shall be listed and labeled in accordance with UL 181A and shall be marked "181A-P" for pressure-sensitive tape, "181 A-M" for mastic or "181 A-H" for heat sensitive tape.

(B) Tapes and mastics used to seal metallic and 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 BM" for mastic. Duct connections to flanges of air distribution system equipment shall be sealed and mechanically fastened. Mechanical fasteners for use with flexible nonmetallic air ducts shall comply with UL 181B and shall be marked 181B-C. Crimps joints for round metallic ducts shall have a contact lap of not less than 1 inch (25 mm) and shall be mechanically fastened by means of not less than three sheet- metal screws or rivets equally spaced around the joint.

(C) Closure systems used to seal all ductwork shall be installed in accordance with the manufacturers' instructions.

(D) Exceptions:
(i) Exception 1: Spray polyurethane foam shall be permitted to be applied without additional joint seals.

(ii) Exception 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.

(iii) Exception 3: For ducts having a static pressure classification of less than 2 inches of water column (500 Pa), additional closure systems shall not be required for continuously welded joints and seams and locking-type joints and seams. This exception shall not apply to snap-lock and button-lock type joints and seams that are located outside of conditioned space.

(iv) Exception 4: For duct systems with sheet metal plenums, Y's and supply boots, only liquid applied sealants complying with UL 181 BM (Mastic or similar) or equivalent method, shall be used to seal inner liners and start collars to plenum and any other seams in system.

Disclaimer: These regulations may not be the most recent version. Oklahoma may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
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