2.11 Additions/Alterations    

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

2.11.1  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 substantively upgraded.

2.11.2  Addition Alone Approach    

The proposed addition alone is modeled the same as a newly constructed building except that the internal gains are prorated to the size of the dwelling and any surfaces such as walls or ceilings that are between the existing building and the addition are modeled not included in the calculations. The addition complies if the proposed design uses equal or less space heating and space cooling 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 not modeled or treated as an adiabatic surfaces. All other features of the addition shall be modeled as for 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 (or Package A, see Section 2.4.1). 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 newly constructed building.

2.11.3  Existing + Addition + Alteration Approach     

Standards §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.

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 in accordance with the rules in the standards that take into account whether altered components meet or exceed the threshold at which point they receive a compliance credit and whether any measures are triggered by altering a given component. For example, when replacing or adding an air handler, outdoor condensing unit of a split system, or cooling or heating coil, the prescriptive requirements include duct leakage testing to 15%.

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.

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

•      Verified and Altered: the surface or system is being altered in the proposed design and the original condition is verified by a HERS rater.

•      New: a new surface or system is added in the proposed design (typically part of the addition, but may be in the existing building).

Features being removed are not included in the proposed design.

When the standard design requirements for existing, altered and new are identical for a particular input, this section uses the term “all”.

The compliance software user shall indicate that an existing + addition + alteration is being modeled and select the correct tag for each surface or system. Features to be altered must be paired with an existing feature. The compliance documentation shall clearly indicate each tag .

The user chooses whether the project is run “Without” or “With Third Party Verification” of an existing condition (see §150.2, Table 150.2-B):

•      Without 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 software ignores the specific attributes of the existing condition, and automatically sets the standard design based solely on the type of surface or system being altered and the climate zone. Energy compliance credit 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. This path is the default user selection.

The existing condition for altered features may be left undefined since the software uses Table 150.1-B to set the standard design.

Example: an existing 2x4 wood frame exterior wall with no insulation is upgraded to include R-15 cavity insulation. The standard design is based on R-13 cavity insulation (U=0.102), the mandatory minimum insulation requirement, and the proposed R-15 in the walls receives an energy credit for the difference between R-13 and R-15.

•      With Third Party Verification of Existing Conditions. This compliance path requires that a HERS Rater perform an on-site inspection of pre-alteration conditions prior to registration of the performance Certificate of Compliance by the HERS Provider Data Registry. If an altered component or system meets or exceeds the prescriptive alteration requirements, the compliance software uses the 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.

The HERS Rater verifies only those existing features that are being altered for compliance credit and used to set the standard design. A summary of the existing measures to be verified are listed on a special Verification of Existing Conditions form (CF3R-20-H) which can be downloaded by the HERS Rater from the HERS Provider website.

In this approach, the existing condition for altered features must be defined by the user since that is used to set the standard design.

Using the same example as above, the standard design is the existing uninsulated wall, and the energy compliance credit is based on the difference between the R-0 wall and the proposed R-15 wall.

Details on the verification of existing conditions are contained in the Residential Compliance Manual, Appendix G.

This subsection presents a summary of standard design modeling assumptions based on proposed design inputs, including whether a proposed feature is new, altered or existing to remain unchanged.

2.11.3.1 Roof/Ceilings    

Standard Design

The standard design roof/ceiling construction assembly is based on the proposed design assembly type as shown in Table 2-23.

Table 2-23: Standard Design for Roofs/Ceilings

2.11.3.2 Exterior Walls    

Proposed Design

Existing structures 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 2-24.

Table 2-24: Standard Design for Exterior Walls

2.11.3.3 Fenestration    

Table 2-25: 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 §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.

Example: A 5’-0” x 6’-8” (33.33 ft²) single pane metal frame sliding door is replaced with a 6’-0” x 6’-8” (40.0 ft²) dual vinyl low-e sliding door. Since the new glass sliding door replaces the full area of the existing glass sliding door, an altered glass door is modeled with an area of 33.33 ft², and a new glass door is modeled with an area of (40.0 - 33.33) = 6.67 ft².

Standard Design

Standard design fenestration area, orientation, U-factor and SHGC are based on the proposed design fenestration as shown in Table 2-25. Vertical glazing includes all fenestration in exterior walls such as windows, clerestories and glazed doors. Skylights include all glazed openings in roofs and ceilings.

The standard design is set for fenestration areas and orientations as:

1.   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.

2.   Proposed design > 20% total fenestration area:

The standard design first calculates the allowed total fenestration area as follows total existing and altered fenestration area in existing or altered walls and roofs + 20% of the addition conditioned floor area.

Example: An existing 2,000 sf house is undergoing alterations and a 400-ft² addition. The existing portion of the house has a total of 560 ft² (28%) of windows, glazed doors and skylights that are existing (unchanged) or altered (replaced) within the exterior walls and roofs to remain. Therefore:

Standard design = 560 + (0.20 x 400) = 560 + 80 = 640 ft²

The standard design is based on 640 ft² of glazing divided among the 4 building surfaces.

2.11.3.4   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 2-26. Treated differently than fixed overhangs and sidefins, exterior shading includes such features as exterior woven or louvered sunscreen, or roll-down awnings or slats as explained in Section 2.5.6.9.

Table 2-26: Standard Design for Overhangs, Sidefins and Other Exterior Shading

2.11.3.5   Window Film    

Proposed Design

A window film is treated as a window replacement for the SHGC value. To determine the SHGC value, use Table 2-27 to calculate the adjusted SHGC value for the program input. If a window film does not have a 10-year warranty, multiply column 3 by column 4 (ignore column 5) and enter the adjusted SHGC value into the software for the window’s altered SHGC value. If a window film has a 10-year warranty, the multiplier in Column 4 is used with the NFRC value in column 5 (ignore column 3) and enter the adjusted SHGC value into the software for the window’s altered SHGC value. It shall be treated as a window replacement.

Table 2-27 Window Film Calculated SHGC

2.11.3.6 Floors    

Standard Design

The standard design for floors is shown in Table 2-28.

Table 2-28: Standard Design for Raised Floor, Slab-on-Grade and Raised Slab

2.11.3.7 Thermal Mass    

Standard Design

The standard design for thermal mass in Existing + Addition + Alteration calculations is the same as for all newly constructed buildings as explained in Section 2.5.4.1.

2.11.3.8 Air Leakage and Infiltration    

Standard Design air leakage and infiltration

The standard design for space conditioning systems is shown in Table 2-29.

Table 2-29: Standard Design for Air Leakage and Infiltration

2.11.3.9 Space Conditioning System    

Standard Design

The standard design for space conditioning systems is shown in Table 2-30.

Table 2-30: Standard Design for Space Conditioning Systems

2.11.3.10 Duct System    

Standard Design

Table 2-31: 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”.

2.11.3.11 Water Heating System    

Standard Design

Table 2-32: Standard Design for Water Heater Systems