2.10 Additions/Alterations

Addition and alteration compliance is based on standards Section150.2. Alterations must model the entire dwelling unit. When there is no addition Section 150.2(b)2 requires at least two components of the residence must be altered. Additions may be modeled as an entirely new building (whole building), addition alone, or as “existing+addition+alteration”.

2.10.1 Whole Building

The entire proposed building, including all additions and/or alterations, is modeled the same as a newly constructed building. The building complies if the proposed design uses equal or less energy than the standard design. This is a difficult standard to meet as the existing building usually does not meet current standards and must be upgraded.

2.10.2 Addition Alone Approach

The proposed addition alone is modeled the same as a newly constructed building except that the internal gains are prorated based on the size of the dwelling. None of the exceptions included for prescriptive additions, which are implemented in the existing plus addition compliance approach (see Section 2.10.3) are given to the addition alone approach (see Standards Section 150.2(a)2.B.) The addition complies if the proposed design uses equal or less space heating, space cooling, and water heating TDV energy than the standard design.

The addition alone approach shall not be used when alterations to the existing building are proposed. Modifications to any surfaces between the existing building and the addition are part of the addition and are not considered alterations.

Proposed Design

The user shall indicate that an addition alone is being modeled and enter the conditioned floor area of the addition. Any surfaces that are between the existing building and the addition are either not modeled or are treated as adiabatic surfaces. All other features of the addition shall be modeled the same as a newly constructed building.

When an existing HVAC system is extended to serve the addition, the proposed design shall assume the same efficiency for the HVAC equipment as the standard design (see Sections 2.4.1 and 2.4.5).

When a dual-glazed greenhouse or garden window is installed in an addition or alteration, the proposed design U-factor can be assumed to be 0.32.

Standard Design

The addition alone is modeled the same as a newly constructed building, with the following exceptions:

A. When roofing requirements are included in Table 150.1-A, they are included in the standard design if the added conditioned floor area is greater than 300 ft².

B. When ventilation cooling (whole-house fan) is required by Table 150.1-A, it is included in the standard design when the added conditioned floor area is greater than 1,000 ft². The capacity shall be based on 1.5 cfm/ft² of conditioned floor area for the entire dwelling unit conditioned floor area.

C. When compliance with indoor air quality requirements of Section 150.0(o) apply to an addition with greater than 1,000 ft² added, the conditioned floor area of the entire dwelling unit shall be used to determine the required ventilation airflow. For additions with 1,000 ft² or less of added conditioned floor area, no indoor air quality requirements shall apply.

2.10.3 Existing + Addition + Alteration Approach

Standards Sections 150.2(a)2 and (b)2 contain the provisions for additions and alterations to be modeled by including the existing building in the calculations. This is called the “Existing + Addition + Alteration” (or “E+A+A”) performance approach.

Proposed Design

The proposed design is modeled by identifying each energy feature as part of the existing building, the addition, or an alteration. The compliance software uses this information to create an E+A+A standard design using the rules in the standards that take into account whether altered components meet or exceed the threshold at which they receive a compliance credit and whether any measures are triggered by altering a given component.

For building surfaces and systems designated below, all compliance software must provide an input field with labels for the proposed design which define how the standard design requirements are established, based on the option selected by the software user:

•      Existing: remains unchanged within the proposed design (both standard design and proposed design have the same features and characteristics).

•      Altered: the surface or system is altered in the proposed design. No verification of existing conditions is assumed.

•      Verified Altered: the surface or system is altered in the proposed design and the original condition is verified by a HERS rater (an optional selection).

•      New: a new surface or system is added in the proposed design may be in the existing building or the addition.

Features removed are not included in the proposed design.

The user chooses whether an altered feature includes “Third Party Verification” of an existing condition (see Section 150.2, Table 150.2-B):

Altered with no third party verification of existing conditions (the default selection). This compliance path does not require an on-site inspection of existing conditions prior to the start of construction. The attributes of the existing condition is undefined, with the standard design for altered components based on Section 150.2, Table 150.2-B and the climate zone. Energy compliance credit or penalty is a function of the difference between the value for that specific feature allowed in Table 150.2-B and the modeled/installed efficiency of the feature.

Verified Altered existing conditions. This compliance path requires that a HERS rater perform an on-site inspection of pre-alteration conditions prior to construction. If an altered component or system meets or exceeds the prescriptive alteration requirements, the compliance software uses the user-defined existing condition as the standard design value. Energy compliance credit is then based on the difference between the verified existing condition for that altered feature and the modeled/installed efficiency of the proposed design.

2.10.3.1 Roof/Ceilings

Standard Design

The standard design roof/ceiling construction assembly is based on the proposed design assembly type as shown in Table 21. For additions less than or equal to 700 square feet, radiant barrier requirements follow Option C (Section 150.1(c)9B). The standard design for unaltered ceilings and roofs is the existing condition.

Table 21: Addition Standard Design for Roofs/Ceilings

2.10.3.2 Exterior Walls

Proposed Design

Existing structures with R-11 insulation that are being converted to conditioned space using an E+A+A approach are allowed to show compliance using R-11 wall insulation, without having to upgrade to R-13 mandatory insulation requirements. The walls are modeled as an assembly with R-11 insulation.

Standard Design

The areas, orientation and tilt of existing, new and altered net exterior wall areas (with windows and doors subtracted) are the same in the existing and addition portions of standard design as the proposed design.

If the proposed wall area is framed, the gross exterior wall area (excluding knee walls) is equally divided between the four building orientations: front, left, back and right. The gross exterior wall area of any unframed walls is also equally divided between the four orientations in the standard design.

The standard design exterior wall construction assembly is based on the proposed design assembly type as shown in Table 22. Framed walls are modeled as 16-inch on center wood framing. The standard design for unaltered walls is the existing condition. The software does not implement the prescriptive provision that allows eliminating continuous insulation for walls being extended to an addition.

Table 22: Addition Standard Design for Exterior Walls

2.10.3.3 Fenestration

Table 23: Addition Standard Design for Fenestration (in Walls and Roofs)

Proposed Design

Fenestration areas are modeled in the addition as new. In the existing building they may be existing, altered or new. Altered (replacement) fenestration is defined in Section 150.2(b)1.B as “existing fenestration area in an existing wall or roof [which is] replaced with a new manufactured fenestration product...Up to the total fenestration area removed in the existing wall or roof....“ Added fenestration area in an existing wall or roof is modeled as new.

Standard Design

Standard design fenestration U-factor and SHGC are based on the proposed design fenestration as shown in Table 23. Vertical glazing includes all fenestration in exterior walls such as windows, clerestories and glazed doors. Skylights include all glazed openings in roofs and ceilings.

New fenestration in an alteration is modeled with the same U-factor and SHGC as required for an addition.

West-facing limitations are combined with maximum fenestration allowed and are not an additional allowance.

The standard design is set for fenestration areas and orientations as shown in Table 23:

•      Proposed design < 20% total fenestration area:

In the existing building, the standard design uses the same area and orientation of each existing or altered fenestration area (in its respective existing or altered wall or roof.)

In the addition, new fenestration is divided equally between the four project compass points similar to new gross wall areas in the addition described above.

Proposed design > allowed % total fenestration area:

The standard design first calculates the allowed total fenestration area as the total existing and altered fenestration area in existing or altered walls and roofs + % of the addition conditioned floor area.

2.10.3.4 Overhangs, Sidefins and Other Exterior Shading

Standard Design

The standard design for a proposed building with overhangs, sidefins and/or other exterior shades is shown in Table 24.  Exterior shading (currently limited to bug screens) is treated differently than fixed overhangs and sidefins as explained as explained in Section 2.5.6.9.

Table 24: Addition Standard Design for Overhangs, Sidefins and Other Exterior Shading

2.10.3.5 Window Film

Proposed Design

A window film must have at least a 10-year warranty and is treated as a window replacement. The values modeled are either the default values from Tables 110.6-A and 110.6-B or the NFRC Window Film Energy Performance Label.

2.10.3.6 Floors

Standard Design

Table 150.2-C requires that the standard design is based on the mandatory requirements from Section 150.0(d) The standard design for floors is shown in Table 25.

Table 25: Addition Standard Design for Raised Floor, Slab-on-Grade and Raised Slab

2.10.3.7 Thermal Mass

Standard Design

The standard design for thermal mass in existing plus addition plus alteration calculations is the same as for all newly constructed buildings as explained in Section 2.5.4.1.

2.10.3.8 Air Leakage and Infiltration

Standard Design air leakage and infiltration

The standard design for space conditioning systems is shown in Table 26.

Table 26: Addition Standard Design for Air Leakage and Infiltration

2.10.3.9 Space Conditioning System

Standard Design

The standard design for space conditioning systems is shown in Table 27.

When cooling ventilation is required by Sections 150.1 and 150.2, the capacity is 1.5 cfm/ft² of conditioned floor area for the entire dwelling unit.

When compliance with indoor air quality requirements of Section 150.0(o) apply to an addition with greater than 1,000 ft² added, the conditioned floor area of the entire dwelling unit is used to determine the required ventilation airflow. For additions with 1,000 ft² or less of added conditioned floor area, no indoor air quality requirements shall apply.

Table 27: Addition Standard Design for Space Conditioning Systems

2.10.3.10 Duct System

Standard Design

Table 28: Addition Standard Design for Duct Systems

Note 1: Refer to Section 150.2(b)1Diia for definition of
an “Entirely New or Complete Replacement Duct System”.

2.10.3.11 Water Heating System

Standard Design

Table 29: Addition Standard Design for Water Heater Systems