2.3 Building Materials and Construction

2.3.1    Materials

Only materials approved by the Energy Commission may be used in defining constructions. Additional materials may be added to the compliance manager.

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

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

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.

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.

The conductivity of insulation materials vary with temperature according to the coefficient listed. Other materials have a coefficient of zero (0), and the conductivity does not vary with temperature.

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.

The density of the material is its weight in pounds per cubic foot.

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

Table 4: Materials List

Source: California Energy Commission

2.3.2    Construction Assemblies

Constructions are defined by the compliance user for use in defining the building. The user assembles a construction from one or more layers of materials, as shown in Figure 3. 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 3: Example Construction Data Screen

The types of assemblies are:

Exterior wall.
Interior wall.
Underground walls.
Attic roof.
Cathedral roof.
Ceiling below attic.
Interior ceiling.
Interior floor.
Exterior floor (over unconditioned space or exterior).
Floor over crawl space.

1.   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 (moving 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 2.4.5.

2.   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.

3.   Roof, structurally insulated panels (SIP).

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

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

6.   Party surfaces separate conditioned space included in the analysis from conditioned space that may or may not be included in the analysis. Party surfaces for spaces that are modeled include surfaces between multifamily dwelling units. 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.

All assemblies have a cavity path and a frame path.

Spray foam insulation R-values are either default values with no special inspection requirements or higher values when supported by an ESR number (see details Section 2.3.3 and RA3.5) verified by a HERS rater.

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

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.

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

All proposed constructions, including insulation, frame type, frame size, and exterior finish or exterior condition are listed on the CF1R. Nonstandard framing (e.g., 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.

Table 5: Required Thickness Spray Foam Insulation

Source: California Energy Commission

Additional documentation and verification requirements for a value other than the default values shown in Table 5 is required. (See RA3.5.6.)

2.3.3.1        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).

2.3.3.2        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).

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).

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

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 RA4.1.7. Furthermore, a HERS verification requirement for the installation of spray foam insulation using higher-than-default values is included on the CF1R.