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 250°F (121°C).
2.
Factory-made ducts shall be listed and labeled in accordance with UL 181 and
installed in accordance with the manufacturer's instructions.
3. Fibrous duct construction shall conform to
the SMACNA Fibrous Glass Duct Construction Standards or NAIMA
Fibrous Glass Duct Construction Standards.
4. Field-fabricated and shop-fabricated metal
and flexible duct constructions shall conform to the SMACNA HVAC Duct
Construction Standards-Metal and Flexible, except as
allowed by Table M1601.1.1. Galvanized steel shall conform to ASTM A
653.
5. Use of gypsum products to
construct return air ducts or plenums is permitted, provided that the air
temperature does not exceed 125°F (52°C) and exposed surfaces are not
subject 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 shall not be used as a duct
or an air plenum in new construction. For existing systems, stud wall cavities
and the spaces between solid floor joists to be used as air plenums shall
comply with the following:
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-space
plenums shall be isolated from adjacent concealed spaces by tight-fitting fire
blocking in accordance with Section R302.11. Fireblocking materials used for
isolation shall comply with Section R302.11.1.
7.5. Stud wall cavities in the outside walls
of building envelope assemblies shall not be utilized as air plenums.
Notes
Wash. Admin. Code
§
51-51-1600
Amended by
WSR
16-03-025, Filed 1/11/2016, effective
7/1/2016
Amended by
WSR
23-23-104, Filed 11/15/2023, effective
3/16/2024
Statutory Authority:
RCW
19.27.031 and
chapters
19.27 and
34.05 RCW. 13-04-068, §
51-51-1600, filed 2/1/13, effective 7/1/13. Statutory Authority:
RCW
19.27.031 and
19.27.074. 10-03-098, §
51-51-1600, filed 1/20/10, effective
7/1/10.