2.3  Building Materials and Construction

2.3.1          Materials

Only materials approved by the CEC may be used in defining constructions. Additional materials may be added to the compliance manager through an exceptional method application, as outlined in Section 10-109(e) and Section 10-110.

Table 4 shows a partial list of the materials available for construction assemblies.

Material Name

The material name is used to select the material for a construction.

Thickness

Some materials, such as three-coat stucco, are defined with a specific thickness (not editable by the compliance user). The thickness of other materials, such as softwood used for framing, is selected by the compliance user based on the construction of the building.

Conductivity

The conductivity of the material is the steady-state heat flow per square foot, per foot of thickness, or per degree Fahrenheit temperature difference. It is used in simulating the heat flow in the construction.

Table 4: Materials List

Source: California Energy Commission

Coefficient for Temperature Adjustment of Conductivity

The conductivity of some materials varies with temperature according to the coefficient listed. Materials that have a coefficient of zero (0) do not vary with temperature.

Specific Heat

The specific heat is the amount of heat in British thermal units (Btu) it takes to raise the temperature of 1 pound of the material 1 degree Fahrenheit (Btu/lb-°F).

Density

The density of the material is the weight of the material in pounds per cubic foot (lb/ft³).

R-value per inch

The R-value per inch is the resistance to heat flow for a 1-inch thick material.

2.3.2          Construction Assemblies

“Constructions” are defined by the compliance software user to characterize the envelope performance of the building. The user assembles a construction from one or more layers of materials, as shown in Figure 5: Example Construction Data Screen. For framed constructions, there is a framing layer that has parallel paths for the framing and the cavity between the framing members. The layers that are allowed depend on the surface type. The compliance manager calculates a winter design U-factor that is compared to a construction that meets the prescriptive standard. The U-factor is displayed as an aid to the user. The calculations used in the energy simulation are based on each layer and framing rather than the U-factor.

Figure 5 Example Construction Data Screen

Source: California Energy Commission

Assembly Types

The types of assemblies are:

•    Exterior wall.

•    Interior wall.

•    Underground wall.

•    Attic roof.

•    Cathedral roof.

•    Ceiling below attic.

•    Interior ceiling.

•    Interior floor.

•    Exterior floor (over unconditioned space or exterior).

•    Floor over crawl space.

Construction Type

The types of construction are:

Ø Ceiling below attic (the roof structure is not defined here, but is part of the attic), wood-framed. In a residence with a truss roof, the ceiling is where the insulation is located, while the structure above the ceiling is encompassed by the term “attic” or “roof.” The attic or roof consists of (from inside to outside) the radiant barrier, below-deck insulation, framing, above-deck insulation, and the roofing product, such as asphalt or tile roofing. See more in Section 2.6.2 Ceiling Below Attic.

Ø Cathedral ceiling (with the roof defined as part of the assembly), wood-framed. Since there is no attic, the roof structure is connected to the insulated assembly at this point.

Ø Roof, structurally insulated panels (SIP).

Ø Walls (interior, exterior, underground), wood- or metal-framed, or SIP.

Ø Floors (over exterior, over crawl space, or interior).

Ø Party surfaces separate conditioned space included in the analysis from conditioned space not included in the analysis. Party surfaces for spaces not included in the analysis include spaces joining an addition alone to the existing dwelling. Interior walls, ceilings, or floors can be party surfaces.

Construction Layers

All assemblies have a cavity path and a frame path.

As assemblies are completed, the screen displays whether the construction meets the prescriptive requirement for that component.

Proposed Design

The user defines a construction for each surface type included in the proposed design. Any variation in insulation R-value, framing size or spacing, interior or exterior sheathing, or interior or exterior finish requires the user to define a different construction. Insulation R-values are based on manufacturer-rated properties rounded to the nearest whole R-value. Layers such as sheetrock, wood sheathing, stucco, and carpet whose properties are not compliance variables are included as generic layers with standard thickness and properties.

Walls separating the house from an attached unconditioned attic or garage are modeled as interior walls with unconditioned space as the adjacent zone, which the compliance manager recognizes as a “demising wall.” Floors over a garage are modeled as an interior or demising floor. The exterior walls, floor, and ceiling/roof of the garage are modeled as part of the unconditioned garage zone.

Standard Design

The compliance software assembles a construction that meets the prescriptive standards for each user-defined construction or assembly.

Verification and Reporting

All proposed constructions, including insulation, frame type, frame size, and exterior finish or exterior condition, are listed on the CF1R. Nonstandard framing (for example, 24” on center wall framing, advanced wall framing) is reported as a special feature.

2.3.3          Spray-Foam Insulation

The R-values for spray-applied polyurethane foam (SPF) insulation differ depending on whether the product is open cell or closed cell. Spray-foam insulation R-values are calculated based on the nominal thickness of the insulation multiplied by the default thermal resistivity per inch, or the total R-value may be calculated based on the thickness of the insulation multiplied by the tested R-value per inch as certified by the Department of Consumer Affairs, Bureau of Household Goods and Services. (See details Section 2.3.3 Spray-Foam Insulation and Reference Appendices, Residential Appendix RA3.5.) Additional documentation and verification requirements for a value other than the default values shown in Table 5: Required Thickness Spray-Foam Insulation (in inches) are required. (See RA3.5.6.)

Table 5: Required Thickness Spray-Foam Insulation (in inches)

Source: California Energy Commission

Medium-Density Closed-Cell SPF Insulation

The default R-value for spray-foam insulation with a closed cellular structure is R-5.8 per inch, based on the installed nominal thickness of insulation. Closed-cell insulation has an installed nominal density of 1.5 to 2.5 pounds per cubic foot (pcf).

Low-Density Open-Cell SPF Insulation

The default R-value for spray-foam insulation with an open cellular structure is calculated as R-3.6 per inch, based on the nominal required thickness of insulation. Open-cell insulation has an installed nominal density of 0.4 to 1.5 pounds per cubic foot (pcf).

Proposed Design

The user will select either typical values for open-cell or closed-cell spray-foam insulation or higher-than-typical values and enter the total R-value (rounded to the nearest whole value).

Standard Design

The compliance software assembles a construction that meets the prescriptive standards for each assembly type (ceiling/roof, wall, and floor).

Verification and Reporting

When the user elects to use higher-than-typical R-values for open-cell or closed-cell spray-foam insulation, a special features note is included on the CF1R requiring documentation requirements specified in Reference Appendices, Joint Appendix JA4.1.7. Furthermore, a HERS Verification requirement for the installation of spray-foam insulation using higher-than-default values is included on the CF1R.