Washington Administrative Code › Title 51 - Enterprise Services, Department of (Building Code Council) › Chapter 51-11C - State Building Code adoption and amendment of the 2021 edition of the International Energy Conservation Code, Commercial › Section 51-11C-61022 - Section A102.2-Component description

Current through Register Vol. 24-14, July 15, 2024
A102.2 Component description.
The four types of
				ceilings are characterized as follows:
A102.2.1 Ceilings below a vented attic.
Attic
				insulation is assumed to be blown-in, loose-fill fiberglass with a K-value of
				2.6 h " ft2 " °F/Btu per inch. Full bag count
				for specified Rvalue is assumed in all cases. Ceiling dimensions for flat
				ceiling calculations are 45 by 30 feet, with a gabled roof having a 4/12 pitch.
				The attic is assumed to vent naturally at the rate of 3 air changes per hour
				through soffit and ridge vents. A void fraction of 0.002 is assumed for all
				attics with insulation baffles. Standard-framed, unbaffled attics assume a void
				fraction of 0.008.
Attic framing is either standard or advanced. Standard framing
				assumes tapering of insulation depth around the perimeter with resultant
				decrease in thermal resistance. An increased R-value is assumed in the center
				of the ceiling due to the effect of piling leftover insulation. Advanced
				framing assumes full and even depth of insulation extending to the outside edge
				of exterior walls. Advanced framing does not change from the default
				value.
U-factors for flat ceilings below vented attics with standard
				framing may be modified with the following table:
Roof Pitch
U-Factor for Standard Framing
R-30
R-38
4/12
0.036
0.031
5/12
0.035
0.030
6/12
0.034
0.029
7/12
0.034
0.029
8/12
0.034
0.028
9/12
0.034
0.028
10/12
0.033
0.028
11/12
0.033
0.027
12/12
0.033
0.027
Vented scissors truss attics assume a ceiling pitch of 2/12
				with a roof pitch of either 4/12 or 5/12. Unbaffled standard framed scissors
				truss attics are assumed to have a void fraction of 0.016.
A102.2.2 Vaulted ceilings.
Insulation is assumed
				to be fiberglass batts installed in roof joist cavities. In the vented case, at
				least 1.5 inches between the top of the batts and the underside of the roof
				sheathing is left open for ventilation in each cavity. A ventilation rate of
				3.0 air changes per hour is assumed. In the unvented or dense pack case, the
				ceiling cavity is assumed to be fully packed with insulation, leaving no space
				for ventilation.
A102.2.3 Roof decks.
Rigid insulation is applied
				to the top of roof decking with no space left for ventilation. Roofing
				materials are attached directly on top of the insulation. Framing members are
				often left exposed on the interior side.
A102.2.4 Metal truss framing.
Overall system
				tested values for the roof/ceiling Uo for metal framed
				truss assemblies from approved laboratories shall be used, when such data is
				acceptable to the building official.
Alternatively, the Uo for roof/ceiling
				assemblies using metal truss framing may be obtained from Tables A102.2.4 (1)
				through A102.2.4(5).
A102.2.5 Metal building roof.
Table A102.2.5: The
				base assembly is a roof where the insulation is compressed when installed
				beneath metal roof panels attached to the steel structure (purlins). Additional
				assemblies include continuous insulation, uncompressed and uninterrupted by
				framing.
U-factors for metal building roofs shall be taken from Table
				A102.2.5, provided the average purlin spacing is at least 52 inches and the
				R-value of the thermal spacer block is greater than or equal to the thermal
				spacer block R-value indicated in Table A107.2.5 for the assembly. It is not
				acceptable to use the U-factors in Tables A102.2.6(1), A102.2.6(2) and
				A102.2.6(3) if additional insulated sheathing is not continuous.
A102.2.5.1 Single layer.
The rated R-value of
				insulation is for insulation installed perpendicular to and draped over purlins
				and then compressed when the metal roof panels are attached. A minimum R-3
				(R-0.5) thermal spacer block between the purlins and the metal roof panels is
				required, unless compliance is shown by the overall assembly U-factor.
A102.2.5.2 Double layer.
The first rated R-value
				of insulation is for insulation installed perpendicular to and draped over
				purlins. The second rated R-value of insulation is for unfaced insulation
				installed above the first layer and parallel to the purlins and then compressed
				when the metal roof panels are attached. A minimum R-3 (R-0.5) thermal spacer
				block between the purlins and the metal roof panels is required, unless
				compliance is shown by the overall assembly U-factor.
A102.2.5.3 Continuous insulation.
For continuous
				insulation (e.g., insulation boards or blankets), it is assumed that the
				insulation is installed below the purlins and is uninterrupted by framing
				members. Insulation exposed to the conditioned space or semi-heated space shall
				have a facing, and all insulation seams shall be continuously sealed to provide
				a continuous air barrier.
A102.2.5.4 Liner system (Ls).
A continuous
				membrane is installed below the purlins and uninterrupted by framing members.
				Uncompressed, unfaced insulation rests on top of the membrane between the
				purlins. For multilayer installations, the last rated R-value of insulation is
				for unfaced insulation draped over purlins and then compressed when the metal
				roof panels are attached. A minimum R-3 (R-0.5) thermal spacer block between
				the purlins and the metal roof panels is required, unless compliance is shown
				by the overall assembly U-factor.
A102.2.5.5 Filled cavity.
The first rated R-value
				of insulation is for faced insulation installed parallel to the purlins. The
				second rated R-value of insulation is for unfaced insulation installed above
				the first layer, parallel to and between the purlins and compressed when the
				metal roof panels are attached. The facer of the first layer of insulation is
				of sufficient width to be continuously sealed to the top flange of the purlins
				and to accommodate the full thickness of the second layer of insulation. A
				supporting structure retains the bottom of the first layer at the prescribed
				depth required for the full thickness of the second layer of insulation being
				installed above it. A minimum R-5 (R-0.9) thermal spacer block between the
				purlins and the metal roof panels is required, unless compliance is shown by
				the overall assembly U-factor.
A102.2.6 Roofs with insulation entirely above deck
				(uninterrupted by framing).
Tables A102.2.6(1) through A102.2.6(3): The
				base assembly is continuous insulation over a structural deck. These tables
				indicate effective U-factors for tapered roof insulation, sloped from a maximum
				R-value (Rmax) at the peak of the slope to a minimum
				R-value (Rmin) at the low point of the slope. The rows
				of the tables represent the rated R-value of the insulation at the minimum
				conditions (except at roof drains) and the columns of the table represent the
				rated R-value of the insulation at the maximum conditions. The slope of the
				tapered insulation shall be no greater than 1/4 inch per
				foot.
Statutory Authority:
				  RCW
				    19.27A.020,
				  19.27A.025 and
				  chapters
				  19.27 and
				  34.05 RCW. 13-04-056, §
				  51-11C-61022, filed 2/1/13, effective
				  7/1/13.