ENERGY STAR requires that ceiling, wall, floor, and slab insulation levels shall comply with one of the following options:
- Meet or exceed 2009 IECC levels OR
- Achieve ≤133% of the total UA resulting from the U-factors in 2009 IECC Table 402.1.3, excluding fenestration and per guidance in note “d” below, AND home shall achieve ≤ 50% of the infiltration rate in Exhibit 1 of the National Program Requirements.
This guide desctibes complying with both of these options.
Option A is considered the prescriptive approach. Following Option A, insulation R-Values installed in the home must meet or exceed the values in the table below, which has been adapted from the 2009 IECC.
Table 1. Minimum Insulation Levelsa for New Homes as Required by the 2009 International Energy Conservation Code (IECC)
Click here for additional information about building energy codes.
Exceptions to Option A
ENERGY STAR includes some exceptions to these requirements, as outlined below. The exception for ceilings with attic spaces (from note b below) is included because the 2009 IECC assumes standard truss systems. The code allows a “credit” in the form of a reduced R-value requirement if insulation is allowed to be installed full height over the exterior wall plate line (e.g., raised heel truss). In ceilings without attic spaces (from note c below), the design of the roof/ceiling assembly does not allow sufficient space for the required insulation, so the code sets the requirements for those spaces at R-30 but limits the area to which this reduced R-value can apply to 500 ft2 or 20% of the total insulated ceiling area, whichever is less. Specifically, the exceptions are as follows and match footnote 3 in the ENERGY STAR Qualified Homes Thermal Enclosure System Rater Checklist:
- Steel-frame ceilings, walls, and floors shall meet the insulation requirements of the 2009 IECC Table 402.2.5. In CZ 1 and 2, the continuous insulation requirements in this table shall be permitted to be reduced to R-3 for steel-frame wall assemblies with studs spaced at 24 inch on center. This exception shall not apply if the alternative calculations in "d" below are used;
- For ceilings with attic spaces, R-30 shall satisfy the requirement for R-38 and R-38 shall satisfy the requirement for R-49 wherever the full height of uncompressed insulation at the lower R-value extends over the wall top plate at the eaves. This exemption shall not apply if the alternative calculations in "d" are used;
- For ceilings without attic spaces, R-30 shall satisfy the requirement for any required value above R-30 if the design of the roof/ceiling assembly does not provide sufficient space for the required insulation value. This exemption shall be limited to 500 square feet or 20% of the total insulated ceiling area, whichever is less. This exemption shall not apply if the alternative calculations in "d" are used;
- [As described in Option B below] An alternative equivalent U-factor or total UA calculation may also be used to demonstrate compliance, as follows:
d.1. An assembly with a U-factor equal or less than specified in 2009 IECC Table 402.1.3 complies.
d.2 A total building thermal envelope UA that is less than or equal to the total UA resulting from the U-factors in Table 402.1.3 also complies. The insulation levels of all non-fenestration components (i.e., ceilings, walls, floors, and slabs) can be traded off using the UA approach under both the Prescriptive and the Performance Path. Note that fenestration products (i.e., windows, skylights, doors) shall not be included in this calculation. Also, note that while ceiling and slab insulation can be included in trade-off calculations, the R-value must meet or exceed the minimum values listed in Items 4.1 through 4.3 of the ENERGY STAR Checklist to provide an effective thermal break, regardless of the UA tradeoffs calculated. The UA calculation shall be done using a method consistent with the ASHRAE Handbook of Fundamentals and shall include the thermal bridging effects of framing materials. The calculation for a steel-frame envelope assembly shall use the ASHRAE zone method or a method providing equivalent results, and not a series-parallel path calculation method.
Additional Information Related to Option A
Slab edge insulation is allowed to be cut at a 45-degree bevel cut to avoid bringing the insulation to the top of the slab edge so a carpet tack strip can be attached.
Option B is similar to Option A, but it uses U-factors instead of R-values and allows some tradeoffs among the envelope components.
Calculating the Total Building Thermal Envelope UA (for Option B)
To use Option B for quality-installed insulation, the U-factor of each entire assembly (e.g., framed wall) must be equal to or less than the U-factor specified in Table 402.1.3 of the 2009 IECC (see Table 2 below). The entire assembly refers to framing, air films, insulation, etc., not just the insulation installed in the component as in Option A. Option B might be chosen instead of Option A if the home is using an innovative or less common construction technique such as log walls.
Table 2. Equivalent U-Factorsa Adapted from 2009 IECC Table 402.1.3
Option B requires the total building thermal envelope UA (U-factor x area) excluding the fenestration components (windows and doors) to be calculated, and that total UA must be less than or equal to 133% of the total UA resulting from the U-factors in Table 2 (also excluding fenestration). This option allows you to trade off some of the insulation for ceilings, walls, and foundation assemblies as long as you achieve 50% better infiltration than required per Exhibit 1 of the National Program Requirements.
The UA calculation must be done using a method consistent with the ASHRAE Handbook of Fundamentals and include the thermal bridging effects of framing materials (see below for different requirements for steel-frame assemblies). DOE’s REScheck software, meets these requirements and can be used to determine whether the home will achieve ≤ 133% of the total UA. To use REScheck for this purpose, follow these steps:
Select 2009 IECC from the Code menu.
Select the home’s location and enter the conditioned floor area on the Project screen.
Enter only ceiling, wall, and foundation components on the Envelope screen. Do NOT enter windows or doors.
Review the REScheck compliance results. As long as you are no more than 33% worse than code, you have met the first part of the requirement.
Steel-Frame Assemblies for Option B
The calculation for steel-frame envelope assemblies must use the ASHRAE zone method or a method providing equivalent results, and not a series-parallel path calculation method. There are online calculators to help with these methods.
Infiltration Rate Requirements for Option B
In order to use Option B, your envelope, exclusive of fenestration, must have a UA ≤ 133% of the total UA as described above AND meet the infiltration rates of the last column in Table 3.
Table 3. Infiltration Rates as Adapted from the ENERGY STAR National Program Requirements