C402.2.1
Roof
assembly. The minimum thermal resistance (
R-value) of
the insulating material installed either between the roof framing or
continuously on the roof assembly shall be as specified in Table C402.1.3,
based on construction materials used in the roof assembly.
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EXCEPTIONS:
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1. Where tapered insulation is used with insulation
entirely above deck, those roof assemblies shall show compliance on a U-factor
basis per Section C402.1.4. The effective U-factor shall be determined through
the use of Tables A102.2.6(1), A102.2.6(2) and A102.2.6(3).
2. Two layers of insulation are not required where
insulation tapers to the roof deck, such as at roof drains. At roof drains, the
immediate 24 inch by 24 inch plan area around each roof drain has a minimum
insulation requirement of R-13, but otherwise is permitted to be excluded from
the roof insulation area-weighted calculations.
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C402.2.1.1
Minimum thickness, lowest point. The minimum thickness of
above-deck roof insulation at its lowest point, gutter edge, roof drain or
scupper, shall be not less than 1 inch (25 mm).
C402.2.1.2
Suspended ceilings.
Insulation installed on suspended ceilings having removable ceiling tiles shall
not be considered part of the minimum thermal resistance
(R-value) of roof insulation in roof/ ceiling
construction.
C402.2.1.3
Skylight curbs. Skylight curbs shall be insulated to the level of
roofs with insulation entirely above deck or R-5, whichever is less.
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EXCEPTION:
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Unit skylight curbs included as a component of a
skylight listed and labeled in accordance with NFRC 100 shall not be required
to be insulated.
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C402.2.1.4
Rooftop HVAC equipment
curbs. Structural curbs installed to support rooftop HVAC equipment are
allowed to interrupt the above roof insulation. The area under the HVAC
equipment inside of the equipment curb shall be insulated to a minimum of R-13
in all locations where there are not roof openings for ductwork. The annular
space between the roof opening and the ductwork shall be sealed to maintain the
building air barrier. The plan-view area of the HVAC equipment curb shall be
excluded from the prescriptive roof insulation requirements or the
area-weighted component performance calculations.
Notes
Wash. Admin. Code §
51-11C-40221
Amended by
WSR
16-03-072, Filed 1/19/2016, effective
7/1/2016
Amended by
WSR
19-24-040, Filed 11/26/2019, effective
7/1/2020
Amended by
WSR
22-14-091, Filed 7/1/2022, effective
7/1/2023
Statutory Authority:
RCW
19.27A.020,
19.27A.025 and
chapters
19.27 and
34.05 RCW. 13-04-056, §
51-11C-40221, filed 2/1/13, effective
7/1/13.
