2.2 The Building

The building is defined through entries for zones, surfaces, and equipment. Zone types include attic, conditioned space, crawl space, basements, and garages. The roof (such as asphalt shingles or tile) is defined as either part of the attic or as part of a cathedral ceiling (also called a rafter roof). The software models Surfaces separating conditioned space from exterior or unconditioned spaces (such as a garage or storage) as interior surfaces adjacent to the unconditioned zone. Exterior surfaces of an attached garage or storage space are modeled as part of the unconditioned zone.

The input file will include entries for floor areas, wall, door, roof and ceiling areas, and fenestration and skylight areas, as well as the water heating, space-conditioning, ventilation, and distribution systems.

Each surface area is entered along with performance characteristics, including building materials, U-factor and SHGC. The orientation and tilt (Figure 2) are required for envelope elements.

Building elements are to be consistent with the actual building design and configuration.

To determine the standard design for low-rise buildings, the software creates a building with the same general characteristics (number of stories, attached garage, climate zone) and with wall and window areas distributed equally among the four main compass points. Energy features are set to be equal to Section 150.1(c) and Table 150.1-A for single-family houses or Table 150.1-B for multifamily buildings. For additions and alterations, the standard design for existing features in the existing building shall have the same wall and fenestration areas and orientations as the proposed building. The details are below.

All inputs that are used to establish compliance requirements are reported on the CF1R for verification.

To determine the reference design for low-rise buildings, a building with the same general inputs, assumptions and algorithms as the standard design building is modeled except for the following requirements:

b. Wall construction. Climate Zones 2-15 have 2x4 R-13 walls. Climate Zones 1 and 16 have 2x6 R-19 walls.

c. Roof/ceiling construction. Climate Zones 2-15 have R-30 ceiling. Climate Zones 1 and 16 have R-38 ceiling. No climate zones include radiant barriers or cool roofs.

d. Floor construction. Climate Zones 2-15 have 2x10 R-19 floors. Climate Zones 1 and 16 have 2x10 R-30 floors.

e. Slab edge insulation. Climate Zones 1 and 16 include R-10 insulation 24 inches deep.

f. Window U-factors. Climate Zones 2-15 have a U-factor of 0,65. Climate Zones 1 and 16 have a U-factor of 0.35.

h. Window area. When the window area is below 18 percent of the floor area, the reference design has the same area as the proposed design. Above 18 percent, the reference design has 18 percent.

i. HVAC equipment efficiencies. HVAC equipment meets NAECA requirements in effect in 2006 such as 78 percent AFUE for gas central furnace, 13 SEER for central AC.

j. Water heating efficiency. Water heating modeled as a 40-gallon storage water with a 0.594 Energy Factor if gas or a 0.9172 Energy Factor if electric.

2.2.1 Climate and Weather

The user specifies the climate zone based on the zip code of the proposed building. Compliance requirements, weather, design temperatures, and time-dependent valuation (TDV) of energy factors are a function of the climate zone. Compliance software assumes that the ground surrounding residential buildings has a reflectivity of 20 percent in summer and winter.

The zip code and climate zone of the proposed design are reported on the CF1R for verification.

2.2.2 Standards Version

This input determines the appropriate federal appliance efficiency requirement for the standard design to compare with the proposed design.

The standard design cooling equipment efficiency is based on the federal requirements. A minimum SEER and EER (if applicable) that meet the current standard for the type of equipment is modeled.

2.2.3 Existing Condition Verified

These inputs are used for additions and alterations. The standard design assumption for existing conditions vary based on whether the existing conditions are verified by a home energy rating system (HERS) rater before construction. See Section 2.10.4 for more information.

The user inputs either yes or no. “Yes” indicates that the existing building conditions verified by a HERS rater. The default assumption is “no.”

The standard design assumption is based on Section 150.2(b), Table 150.2-C. If the user input is “no,” the standard design for the existing component is based on the value in the second column. If the proposed design response is “yes,” the standard design value for the existing components is the value in the third column.

Verification of existing conditions is a special feature and is reported in the HERS required verification listings on the CF1R.

2.2.4 Air Leakage and Infiltration

Air leakage is a building level characteristic. The compliance software distributes the leakage over the envelope surfaces in accordance with the building configuration and constructs a pressure flow network to simulate the airflows between the conditioned zones, unconditioned zones, and outside.

The airflow through a blower door at 50 pascal (Pa) of pressure measured in cubic feet per minute is called CFM50. CFM50 x 60 minutes divided by the volume of conditioned space is the air changes per hour at 50 Pa, called ACH50.

Specific data on ACH50 may be entered if the single-family home or townhouse will have verified building air leakage testing. In multifamily buildings, due to the lack of an applicable measurement standard, ACH50 is fixed at the above defaults.

ACH50 defaults to 5 for new construction in single-family houses and townhomes and 7 for all other buildings that have heating and cooling system ducts or both outside conditioned space and for buildings with no cooling system. In single-family homes and townhomes with no heating or cooling system ducts or both in unconditioned space, the default ACH50 is 4.4 and 6.2 for all others.

Specific data on ACH50 may be entered if the single-family home or townhouse will have verified building air leakage testing. User input of an ACH50 that is less than the default value becomes a special feature requiring HERS verification.

Due to the lack of an applicable measurement standard, ACH50 is fixed at the above defaults and is not a compliance variable in multi-family buildings.

The standard design shall have 5 ACH50 for single-family home and 7 for other buildings (ducted space-conditioning).

When the user chooses verified building air leakage testing (any value less than the standard design), diagnostic testing for reduced infiltration, with details and target values modeled in the proposed design, is reported in the HERS required verification listing on the CF1R.

The compliance software creates an air leakage network for the proposed and standard design using the building description. Air leakage is distributed across the envelope surfaces according to the factors in Table 2. The air network is insensitive to wind direction. For buildings modeled with multiple conditioned zones, either a 20-square-foot open door or 30-square-foot open stairwell (in a multistory building) is assumed between any two conditioned zones.

The only difference between the air network for the proposed and standard designs is the ACH50 if the user specifies a value lower than the default.

Multifamily buildings that have floors between dwelling units must define each floor as a separate zone or each dwelling unit as a separate zone.

Table 2: Air Leakage Distribution

Configuration	% of Total Leakage by Surface
Configuration	Ceilings	Floors	Exterior Walls	House to Garage Surfaces
Slab on Grade	50	0
Raised Floor	40	10
No Garage			50	0
Attached Garage			40	10

2.2.5 Quality Insulation Installation (QII)

The compliance software user may specify quality insulation installation (QII) for the proposed design as yes or no. The effective R-value of cavity insulation is reduced as shown in Table 3 in buildings with no QII. When set to no, framed walls, ceilings, and floors are modeled with added winter heat flow between the conditioned zone and attic to represent construction cavities open to the attic. QII does not affect the performance of continuous sheathing in any construction.

The compliance software user may specify compliance with QII. The default is “no” for QII.

The standard design is modeled with “yes” for verified QII for newly constructed single-family low-rise houses and additions greater than 700 square feet in all climate zones, for multifamily low-rise residential buildings and additions greater than 700 square feet in Climate Zones 1-6 and 8-16. (Climate Zone 7 has no QII for multifamily buildings.)

For alterations to existing pre-1978 construction, if the existing wall construction is assumed to have no insulation, no wall degradation is assumed for the existing wall.

Table 3: Modeling Rules for Unverified Insulation Installation Quality

Component	Modification
Walls, Floors, Attic Roofs, Cathedral Ceilings	Multiply the cavity insulation R-value/inch by 0.7.
Ceilings Below Attic	Multiply the blown and batt insulation R-value/inch by 0.96-0.00347*R.
Ceilings Below Attic	Add a heat flow from the conditioned zone to the attic of 0.015 times the area of the ceiling below attic times (the conditioned zone temperature - attic temperature) whenever the attic is colder than the conditioned space.

2.2.6 Number of Bedrooms

The number of bedrooms in a building is used to establish the indoor air quality (IAQ) mechanical ventilation requirements and to determine if a building qualifies as a compact building for incentive programs.

The standard design shall have the same number of bedrooms as the proposed design.

2.2.7 Dwelling Unit Types

Internal gains and IAQ ventilation calculations depend on the conditioned floor area and number of bedrooms. For multifamily buildings with individual IAQ ventilation systems, each combination of bedrooms and conditioned floor area has a different minimum ventilation CFM that must be verified. In buildings with multiple dwelling units, a dwelling unit type has the same floor area, number of bedrooms, and appliances (washer/dryer in the dwelling unit).

The standard design shall have the same number and type of dwelling units as the proposed design.

The number of units of each type and minimum IAQ ventilation for each unit is reported on the CF1R for field verification.

2.2.8 Front Orientation

The input for the building front orientation is the actual azimuth of the front of the building. This azimuth will generally be the side of the building facing the street or where the front door is located. The orientations of the other sides of a building viewed from the outside looking at the front door are called front, left, right, back, or a value relative to the front, and the compliance software calculates the actual azimuth from this input. Multiple orientation compliance can be selected for newly constructed buildings only.

The user specifies whether compliance is for multiple orientations or for a site-specific orientation. For site-specific orientation, the user inputs the actual azimuth of the front in degrees from true north.

The compliance software constructs a standard design building that has 25 percent of the proposed model wall and window areas facing each cardinal orientation regardless of the proposed model distribution of wall and window area.

A typical reported value would be "290 degrees (west)." This value would indicate that the front of the building faces north 70° west in surveyors’ terms. The closest orientation on 45° compass points should be reported in parentheses (for example, north, northeast, east, southeast, south, southwest, west, or northwest). When compliance is shown for multiple orientations, "all orientations" or “cardinal” is reported as a special feature on the CF1R and the energy use results are reported for four orientations including north, east, south, and west.

2.2.9 Gas Type

For newly constructed buildings, the standard design fuel type is based on the proposed design fuel type. The user specifies natural gas (if available) or propane, whether it is used for cooking appliances, clothes dryer, heating equipment, or water heating equipment. This specification is to establish the TDV values from Reference Appendices JA3 used by the compliance software to determine standard and proposed design energy use.

For projects with a run scope of “addition alone,” natural gas is available if a gas service line can be connected to the site without a gas main extension. Natural gas is available for existing plus addition/alteration projects if a gas service line is connected to the existing building.

The user specifies either natural gas, if it is available at the site, or propane.

The standard design assumptions for space heating are as defined in Section 2.4.1 and for water heating are defined in Section 2.9.

2.2.10 Attached Garage

The user specifies whether there is an attached garage. The garage zone is modeled as an unconditioned zone (Section 2.8).

The standard design has the same attached garage assumption as the proposed design.

2.2.11 Lighting

The details of the calculation assumptions for lighting loads included Appendix E are based on the Codes and States Enhancement Initiative (CASE) report on plug loads and lighting (Rubin 2016, see Appendix F).

Fraction of portable lighting, power adjustment multiplier and the exterior lighting power adjustment multiplier (watts/ft² – watts per square foot) are fixed assumptions.

No lighting information is reported on the CF1R for compliance with Title 24, Part 6.

2.2.12 Appliances

The details of the calculation assumptions for appliances and plug loads contained in Appendix E are based on the Codes and States Enhancement Initiative (CASE) report on plug loads and lighting (Rubin 2016, see Appendix F).

All buildings are assumed to have a refrigerator, dishwasher, and cooking appliance. Optionally, buildings can have a clothes washer and clothes dryer. The user can select fuel type as gas or electric for the clothes dryer and cooking appliance.

No information for the appliance types listed above is reported on the CF1R for compliance with Title 24, Part 6.