Normative Appendix A Rated R-Value of Insulation and Assembly U-factor, C-Factor, and F-Factor Determinations

This is a normative appendix and is part of this standard

The U-factors, C-factors, F-factors, and heat capacities for typical construction assemblies are included in Sections A2 through A8. These values shall be used for all calculations unless otherwise allowed by Section A1.2. Interpolation between values in a particular table in Normative Appendix A is allowed for rated R-values of insulation, including insulated sheathing. Extrapolation beyond values in a table in Normative Appendix A is not allowed.

If the building official determines that the proposed construction assembly is not adequately represented in Sections A2 through A8, the applicant shall determine appropriate values for the assembly using the assumptions in Section A9. An assembly is deemed to be adequately represented if

1. the interior structure, hereafter referred to as the base assembly, for the class of construction is the same as described in Sections A2 through A8 and
2. changes in exterior or interior surface building materials added to the base assembly do not increase or decrease the R-value by more than 2 from that indicated in the descriptions in Sections A2 through A8.

Insulation, including insulated sheathing, is not considered a building material.

The buffering effect of suspended ceilings or attic spaces shall not be included in U-factor calculations.

For the purpose of Section A 1.2, the base assembly is continuous insulation over a structural deck. The U-factor includes R-0.17 for exterior air film, R-0 for metal deck, and R-0.61 for interior air film heat flow up. Added insulation is continuous and uninterrupted by framing. The framing factor is zero.

For roofs with insulation entirely above deck, the rated R-value of insulation is for continuous insulation.

U-factors for roofs with insulation entirely above deck shall be taken from Table A2.2.3. It is not acceptable to use these U-factors if the insulation is not entirely above deck or not continuous.

Table A2.2.3 Assembly U-Factors for Roofs with Insulation Entirely Above Deck

For the purpose of Section A1.2, the base assembly is a roof with thermal spacer blocks where the insulation is draped over the steel structure (purlins), spaced nominally 5 ft on center and compressed when the metal roof panels are attached to the steel structure (purlins).

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 thermal spacer block between the purlins and the metal roof panels is required unless compliance is shown by the overall assembly U-factor.

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 thermal spacer block between the purlins and the metal roof panels is required unless compliance is shown by the overall assembly U-factor.

For assemblies with continuous insulation the continuous insulation is installed above or below the purlins, uncompressed and uninterrupted by framing members.

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 thermal spacer block between the purlins and the metal roof panels is required unless compliance is shown by the overall assembly U-factor.

The first rated R-value of insulation represents faced or unfaced insulation installed between the purlins. The second rated R-value of insulation represents unfaced insulation installed above the first layer, perpendicular to the purlins and compressed when the metal roof panels are attached. A supporting structure retains the bottom of the first layer at the prescribed depth required for the full thickness of insulation. A minimum R-5 thermal spacer block between the purlins and the metal roof panels is required unless compliance is shown by the overall assembly U-factor.

U-factors for metal building roofs shall be taken from Table A2.3.3 or determined in accordance with Section A9.2, provided the average purlin spacing for systems with compressed insulation is at least 52 in. U-factors for metal building roof assemblies with average purlin spacing less than 52 in. shall be determined in accordance with Section A9.2. U-factors in Table A2.3.3 shall not be used where the insulation is substantially compressed by the bracing between the purlins.

Table A2.3.3 Assembly U-Factors for Metal Building Roofs

1. A standing seam roof clip that provides a minimum 1.5 in. distance between the top of the purlins and the underside of the metal roof panels is required.
2. A minimum R-3 thermal spacer block is required.
3. A minimum R-5 thermal spacer block is required.

For the purpose of Section A1.2, the base attic roof assembly is a roof with nominal 4 in. deep wood as the lower chord of a roof truss or ceiling joist. The ceiling is attached directly to the lower chord of the truss, and the attic space above is ventilated. Insulation is located directly on top of the ceiling, first filling the cavities between the wood and later covering both the wood and cavity areas. No credit is given for roofing materials. The single-rafter roof is similar to the base attic roof with the key difference being that there is a single, deep rafter to which both the roof and the ceiling are attached. The heat flow path through the rafter is calculated to be the same depth as the insulation. Additional assemblies include continuous insulation uncompressed and uninterrupted by framing. The U-factors include R-0.46 for semiexterior air film, R-0.56 for 0.625 in. gypsum board, and R-0.61 for interior air film heat flow up. U-factors are provided for the following configurations:

1. Attic roof standard framing: Insulation is tapered around the perimeter with a resultant decrease in thermal resistance. Weighting factors are 85% full-depth insulation, 5% half-depth insulation, and 10% joists.
2. Attic roof advanced framing: Full and even depth of insulation extending to the outside edge of walls. Weighting factors are 90% full-depth insulation and 10% joists.
3. Single-rafter roof. An attic roof where the roof sheathing and ceiling are attached to the same rafter. Weighting factors are 90% full-depth insulation and 10% joists.

Table A2.4.2 Single-Rafter Roofs

For attics and other roofs, the rated R-value of insulation is for insulation installed both inside and outside the roof or entirely inside the roof cavity.

Occasional interruption by framing members is allowed but requires that the framing members be covered with insulation when the depth of the insulation exceeds the depth of the framing cavity.

Insulation in such roofs shall be permitted to be tapered at the eaves where the building structure does not allow full depth.

For single-rafter roofs, the requirement is the lesser of the values for attics and other roofs and those listed in Table A2.4.2.

U-factors for attic roofs with wood joists shall be taken from Table A2.4.3. It is not acceptable to use these U-factors if the framing is not wood. For attic roofs with steel joists, see Section A2.5.

Table A2.4.3 Assembly U-Factors for Attic Roofs with Wood Joists

For the purpose of Section A1.2, the base assembly is a roof supported by steel joists with insulation between the joists. The assembly represents a roof in many ways similar to a roof with insulation entirely above deck and a metal building roof. It is distinguished from the metal building roof category in that there is no metal exposed to the exterior. It is distinguished from the roof with insulation entirely above deck in that the insulation is located below the deck and is interrupted by metal trusses that provide thermal bypasses to the insulation. The U-factors include R-0.17 for exterior air film, R-0 for metal deck, and R-0.61 for interior air film heat flow up. The performance of the insulation/framing layer is calculated using the values in Table A9.2-1.

U-factors for attic roofs with steel joists shall be taken from Table A2.5.2. It is acceptable to use these U-factors for any attic roof with steel joists.

Table A2.5.2 Assembly U-Factors for Attic Roofs with Steel Joists (4.0 ft on Center)

Table A3.1-1 Assembly U-Factors for Above-Grade Concrete Walls and Masonry Walls

Table A3.1-2 Assembly U-Factors, C-Factors, R_u, R_c, and HC for Concrete

The U-factors and R_u include standard air film resistances.

The C-factors and R_c are for the same assembly without air film resistances.

Note that the following assemblies do not qualify as a mass wall or mass floor: 3 in. thick concrete with densities of 85, 95, 125, and 135 lb/ft³.

Table A3.1-3 Assembly U-Factors, C-Factors, R_u, R_c, and HC for Concrete Block Walls

Table A3.1-4 Effective R-Values for Insulation/Framing Layers Added to Above-Grade Mass Walls and Below-Grade Walls

For the purpose of Section A1.2, the base assembly is a masonry or concrete wall. Continuous insulation is installed on the interior or exterior or within the masonry units, or it is installed on the interior or exterior of the concrete. The brick cavity wall has continuous insulation between the brick and the concrete or masonry. The U-factors include R-0.17 for exterior air film and R-0.68 for interior air film, vertical surfaces. For insulated walls, the U-factor also includes R-0.45 for 0.5 in. gypsum board. For the cavity wall, the U-factor includes R-0.74 for brick. U-factors are provided for the following configurations:

1. Concrete wall: 8 in. normal weight concrete wall with a density of 145 lb/ft³.
2. Solid grouted concrete block wall: 8 in. medium weight ASTM C90 concrete block with a density of 115 lb/ft³ and solid grouted cores.
3. Partially grouted concrete block wall: 8 in. medium weight ASTM C90 concrete block with a density of 115 lb/ft³ having reinforcing steel every 32 in. vertically and every 48 in. horizontally, with cores grouted in those areas only. Other cores are filled with insulating material only if there is no other insulation.

Mass wall HC shall be determined from Table A3.1-2 or A3.1-3.

The rated R-value of insulation is for continuous insulation uninterrupted by framing other than 20 gage 1 in. metal clips spaced no closer than 24 in. on center horizontally and 16 in. on center vertically.

Where other framing, including metal and wood studs, is used, compliance shall be based on the maximum assembly U-factor.

Where rated R-value of insulation is used for concrete sandwich panels, the insulation shall be continuous throughout the entire panel.

U-factors for mass walls shall be taken from Table A3.1-1 or determined by the procedure in this subsection. It is acceptable to use the U-factors in Table A3.1-1 for all mass walls, provided that the grouting is equal to or less than that specified. HC for mass walls shall be taken from Table A3.1-2 or A3.1-3.

If not taken from Table A3.1-1, mass wall U-factors shall be determined from Tables A3.1-2, A3.1-3, or A3.1-4 using the following procedure:

1. If the mass wall is uninsulated or only the cells are insulated:
   1. For concrete walls, determine the U-factor from Table A3.1-2 based on the concrete density and wall thickness.
   2. For concrete block walls, determine the U-factor from Table A3.1-3 based on the block size, concrete density, degree of grouting in the cells, and whether the cells are insulated.
2. If the mass wall has additional insulation:
   1. For concrete walls, determine the R_c from Table A3.1-2 based on the concrete density and wall thickness. Next, determine the effective R-value for the insulation/framing layer from Table A3.1-4 based on the rated R-value of insulation installed, the thickness of the insulation, and whether it is installed between wood or metal framing or with no framing. Then, determine the U-factor by adding the R_u and the effective R-value together and taking the inverse of the total.
   2. For concrete block walls, determine the R_u from Table A3.1-3 based on the block size, concrete density, degree of grouting in the cells, and whether the cells are insulated. Next, determine the effective R-value for the insulation/framing layer from Table A3.1-4 based on the rated R-value of insulation installed, the thickness of the insulation, and whether it is installed between wood or metal framing or with no framing. Then, determine the U-factor by adding the R_u and the effective R-value together and taking the inverse of the total.

For the purpose of Section A1.2, the base assembly is a wall with metal wall panels and a metal structure. Insulation is installed in accordance with this section. Insulation exposed to a conditioned space or semiheated space shall have a facing with seams overlapped or sealed.

The first rated R-value of insulation is for insulation compressed between metal wall panels and the steel structure.

For assemblies with continuous insulation, the continuous insulation is installed on the outside or inside of the girts, uncompressed and uninterrupted by the framing members.

The insulation is installed in the cavity between the girts, not compressed by the framing. A membrane or facing, installed separately or adhered to the insulation, is installed inside of the girts to form a continuous layer. A thermal spacer block or thermal break strip between the girts and metal wall panels is required when specified in Table A3.2.3.

The first rated R-value of insulation is for insulation installed in the cavity between the girts, not compressed by the framing. The second rated R-value of insulation is for insulation compressed between metal wall panels and the steel structure. A membrane or facing, installed separately or adhered to the insulation, is installed inside of the girts to form a continuous layer. A thermal spacer block or thermal break strip between the girts and metal wall panels is required when specified in Table A3.2.3.

U-factors for metal building walls shall be taken from Table A3.2.3 or determined in accordance with Section A9.2. provided the average girt spacing is at least 52 in. U-factors for metal building wall assemblies with average girt spacing less than 52 in. shall be determined in accordance with Section A9.2.

Table A3.2.3 Assembly U-Factors for Metal Building Walls

(Multiple R-values are listed in order from inside to outside.)

1. A minimum R-0.375 thermal spacer block or thermal break strip is required when installed without continuous insulation.
2. A minimum R-0.75 thermal spacer block or thermal break strip is required when installed without continuous insulation.
3. A minimum R-3 thermal spacer block is required.

For the purpose of Section A1.2, the base assembly is a wall where the insulation is installed within the cavity of the steel stud framing but where there is not a metal exterior surface-spanning member. The steel stud framing is a minimum uncoated thickness of 0.043 in. for 18 gage or 0.054 in. for 16 gage. The U-factors include R-0.17 for exterior air film, R-0.08 for stucco, R-0.56 for 0.625 in. gypsum board on the exterior, R-0.56 for 0.625 in. gypsum board on the interior, and R-0.68 for interior vertical surfaces air film. The performance of the insulation/framing layer is calculated using the values in Table A9.2-2. Additional assemblies include continuous insulation uncompressed and uninterrupted by framing. U-factors are provided for the following configurations:

1. Standard framing: Steel stud framing at 16 in. on center with cavities filled with 16 in. wide insulation for both 3.5 in. deep and 6.0 in. deep wall cavities.
2. Advanced framing: Steel stud framing at 24 in. on center with cavities filled with 24 in. wide insulation for both 3.5 in.deep and 6.0 in. deep wall cavities.

The first rated R-value of insulation is for uncompressed insulation installed in the cavity between steel studs. It is acceptable for this insulation to also be continuous insulation uninterrupted by framing.

If there are two values, the second rated R-value of insulation is for continuous insulation uninterrupted by framing, etc., to be installed in addition to the first insulation.

Opaque mullions in spandrel glass shall be covered with insulation complying with the steel-framed wall requirements.

U-factors for steel-framed walls shall be taken from Table A3.3.3.1.

Table A3.3.3.1 Assembly U-Factors for Steel-Frame Walls

For steel-framed walls with framing at less than 24 in. on center, use the standard framing values as described in Section A3.3.1(a).

For steel-framed walls with framing from 24 to 32 in. on center, use the advanced framing values as described in Section A3.3.1(b).

For steel-framed walls with framing greater than 32 in. on center, use the metal building wall values in Table A3.2.3.

For the purpose of Section A1.2, the base assembly is a wall where the insulation is installed between 2 in. nominal wood framing. Cavity insulation is full depth, but values are taken from Table A9.4.3 for R-19 insulation, which is compressed when installed in a 5.5 in. cavity. Headers are double 2 in. nominal wood framing. The U-factors include R-0.17 for exterior air film, R-0.08 for stucco, R-0.56 for 0.625 in. gypsum board on the exterior, R-0.56 for 0.625 in. gypsum board on the interior, and R-0.68 for interior air film, vertical surfaces. Additional assemblies include continuous insulation uncompressed and uninterrupted by framing. U-factors are provided for the following configurations:

1. Standard framing: Wood framing at 16 in. on center with cavities filled with 14.5 in. wide insulation for both 3.5 in. deep and 5.5 in. deep wall cavities. Double headers leave no cavity. Weighting factors are 75% insulated cavity, 21% studs, plates, and sills, and 4% headers.
2. Advanced framing: Wood framing at 24 in. on center with cavities filled with 22.5 in. wide insulation for both 3.5 in. deep and 5.5 in. deep wall cavities. Double headers leave uninsulated cavities. Weighting factors are 78% insulated cavity, 18% studs, plates, and sills, and 4% headers.
3. Advanced framing with insulated headers: Wood framing at 24 in. on center with cavities filled with 22.5 in. wide insulation for both 3.5 in. deep and 5.5 in. deep wall cavities. Double header cavities are insulated. Weighting factors are 78% insulated cavity, 18% studs, plates, and sills, and 4% headers.

The first rated R-value of insulation is for uncompressed insulation installed in the cavity between wood studs. It is acceptable for this insulation to also be continuous insulation uninterrupted by framing.

If there are two values, the second rated R-value of insulation is for continuous insulation uninterrupted by framing, etc., to be installed in addition to the first insulation.

U-factors for wood-framed walls shall be taken from Table A3.4.3.1.

Table A3.4.3.1 Assembly U-Factors for Wood-Frame Walls 

For wood-framed walls with framing at less than 24 in. on center, use the standard framing values as described in Section A3.4.1(a).

For wood-framed walls with framing from 24 to 32 in. on center, use the advanced framing values as described in Section A3.4.1(b) if the headers are uninsulated, or the advanced framing with insulated header values as described in Section A3.4.1(c) if the headers are insulated.

For wood-framed walls with framing greater than 32 in. on center, U-factors shall be determined in accordance with Section A9.

For the purpose of Section A1.2, the base assembly is 8 in. medium-weight concrete block with a density of 115 lb/ft³ and solid grouted cores. Continuous insulation is installed on the interior or exterior. In contrast to the U-factor for above-grade walls, the C-factor for below-grade walls does not include R-values for exterior or interior air films or for soil. For insulated walls, the C-factor does include R-0.45 for 0.5 in. gypsum board.

C-factors for below-grade walls shall be taken from Table A4.2.1 or determined by the procedure described in this subsection.

Table A4.2.1 Assembly C-Factors for Below-Grade Walls

It is acceptable to use the C-factors in Table A4.2.1 for all below-grade walls.

If not taken from Table A4.2.1, below-grade wall C-factors shall be determined from Tables A3.1-2, A3.1-3, or A3.1-4 using the following procedure:

1. If the below-grade wall is uninsulated or only the cells are insulated:
   1. For concrete walls, determine the C-factor from Table A3.1-2 based on the concrete density and wall thickness.
   2. For concrete block walls, determine the C-factor from Table A3.1-3 based on the block size, concrete density, degree of grouting in the cells, and whether the cells are insulated.
2. If the mass wall has additional insulation:
   1. For concrete walls, determine the R_c from Table A3.1-2 based on the concrete density and wall thickness. Next, determine the effective R-value for the insulation/framing layer from Table A3.1-4 based on the rated R-value of insulation installed, the thickness of the insulation, and whether it is installed between wood or metal framing or with no framing. Then determine the C-factor by adding the R_c and the effective R-value together and taking the inverse of the total.
   2. For concrete block walls, determine the R_c from Table A3.1-3 based on the block size, concrete density, degree of grouting in the cells, and whether the cells are insulated. Next, determine the effective R-value for the insulation/framing layer from Table A3.1-4 based on the rated R-value of insulation installed, the thickness of the insulation, and whether it is installed between wood or metal framing or with no framing. Then determine the C-factor by adding the R_c and the effective R-value together and taking the inverse of the total.