Washington Administrative Code › Title 51 - Enterprise Services, Department of (Building Code Council) › Chapter 51-11R - State Building Code adoption and amendment of the 2021 edition of the International Energy Conservation Code, Residential › Section 51-11R-40210 - Section R402.1-General

Current through Register Vol. 24-14, July 15, 2024
R402.1
General.
The
building thermal envelope
shall meet
			 the requirements of Sections R402.1.1 through R402.1.6.
EXCEPTION:
The following buildings, or portions thereof,
						  separated from the remainder of the building by
building thermal
						  envelope
assemblies complying with this code shall be exempt from the
building thermal envelope
provisions of this code.
1. Those with a peak design rate of energy usage less
						  than 3.4 Btu/h ft2 (10.7
						  W/m2) or 1.0 watt/ft2 of
						  floor area for space conditioning purposes.
2. Those that do not contain
conditioned
						  space
.
3. Greenhouses isolated from any conditioned space and
						  not intended for occupancy.
R402.1.1
Vapor retarder.
Wall assemblies in the
building thermal
			 envelope
shall comply with the vapor retarder requirements of Section
			 R702.7 of the
International Residential Code
or Section 1404.3
			 of the
International Building Code
, as applicable.
R402.1.2
Insulation and fenestration
			 criteria.
The
building thermal envelope
shall meet the
			 requirements of Table R402.1.2 based on the climate zone specified in Chapter
			 3. Assemblies shall have a U-factor equal to or less than that specified in
			 Table R402.1.2. Fenestration shall have a U-factor equal to or less than
			 specified in Table R402.1.2.
R402.1.3
R-value alternative.
Assemblies with
R
-value of insulation materials equal to or
			 greater than that specified in Table R402.1.3 shall be an alternative to the
U
-factor in Table R402.1.2.
R402.1.4
R
-value
			 computation.
Cavity insulation
alone shall be used to
			 determine compliance with the
cavity insulation R
-value
			 requirement in Table R402.1.3. Where
cavity insulation
is
			 installed in multiple layers, the
R
-values of the
cavity insulation
layers shall be summed to determine
			 compliance with the
cavity insulation R
-value requirements.
			 The manufacturer's settled
R
-value shall be used for blown
			 insulation.
Continuous insulation
(ci) alone shall be used to
			 determine compliance with the continuous insulation
R
-value
			 requirements in Table R402.1.3. Where
continuous insulation
is
			 installed in multiple layers, the
R
-values of the
continuous insulation
layers shall be summed to determine
			 compliance with the
continuous insulation R
-value
			 requirements. Computed
R
-values shall not include an
R
-value for other building materials or air films. Where
			 insulated siding is used for the purpose of complying with the continuous
			 insulation requirements of Table R402.1.3, the manufacturer's labeled
R
-value for insulated siding shall be reduced by
			 R-0.6.
R402.1.5
Total UA
			 alternative.
If the proposed
building thermal envelope
UA is less than or equal to the target UA, the building shall be considered in
			 compliance with Table R402.1.2. The proposed UA shall be calculated in
			 accordance with Equation 2. The target UA shall be calculated in accordance
			 with Equation 1.
U
-factors shall be determined as specified in
			 Section R402.1.6. In addition to UA compliance, the maximum fenestration
			 U-factors of Section R402.5 shall be met.
R402.1.6
U
-factor
			 reference and calculations.
The
U
-factors for typical
			 construction assemblies are included in Appendix A in chapter 51-11C WAC. These
			 values shall be used for all calculations. Where proposed construction
			 assemblies are not represented in Appendix A, values shall be calculated in
			 accordance with the ASHRAE
Handbook of Fundamentals
using the
			 framing factors listed in Appendix A where applicable and shall include the
			 thermal bridging effects of framing materials. The SHGC requirements shall be
			 met in addition to UA compliance.
Fenestration
U
-factors shall comply with
				Section R303.1.3, Fenestration product rating.