Install insulation without misalignments, compressions, gaps, or voids along the thermal envelope of the house.
All ceiling, wall, floor, and slab insulation should achieve Grade I level insulation installation criteria as defined by the Residential Energy Services Network (RESNET).
See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and Indoor airPLUS.
Gaps, voids, and compressions that cause the insulation to lose contact with the surface it is intended to insulate can cause cold spots in walls, ceilings, and floors. These cold spots may encourage the formation of condensation in the wall cavity, floors, or ceilings.
The Residential Energy Services Network (RESNET) grades insulation installation quality in its Home Energy Rating System Standards, with Grade 1 being the best installation (RESNET 2013).
Grade 1 Installation requires that insulation material should uniformly fill wall cavities, filling each cavity from side to side and top to bottom, without substantial gaps or voids around obstructions. Batt insulation should be cut to fit around any wiring or piping installed in the wall cavities.
Blown insulation, such as loose fiberglass, cellulose, or mineral wool fibers, flows easily around obstructions, such as wiring and piping, to provide complete coverage in the cavities. To install blown insulation, the open cavities are first covered with a netting that is stapled to the stud faces. A slit is cut in the netting in each cavity and the insulation is installed with a hose inserted through the slit. The installer can easily see where the insulation is going to ensure that each cavity is completely filled without voids.
Spray foam is another option that readily fills areas around obstructions in wall cavities, and it has the advantage of providing both air sealing and insulation. The foam completely fills the open wall cavities and is trimmed flush with the stud faces before installing dry wall. Spray foam insulation is made of petroleum, soy, or castor oil-based polyurethane and is available in open-cell, low-density products or closed-cell, high-density products. Both insulate and air seal; high-density products can also provide a vapor barrier. Another option is sprayed-on cellulose or mineral wool that is mixed with adhesive and water then sprayed into the open cavities and allowed to dry before drywalling.
Additional information about insulation, including descriptions of the many types of insulation available, their R-values, applications and advantages and disadvantages of each kind, and installation guidance can be found in the Building America Best Practices Series Volume 17: Insulation, A Guide for Contractors to Share with Homeowners.
How to Install Insulation to RESNET-Defined Grade I
- Install insulation without misalignments, compressions, gaps, or voids in all wall cavities along the thermal barrier of the house. Figure 1 shows proper installation of batt insulation without gaps or voids. Figure 2 shows incorrect installation; the insulation was not cut to fit around wiring so the insulation will not be in full contact with the drywall along the length of the wall cavities.
- Install wall insulation so that it is enclosed on all six sides in each wall cavity. It should completely fill the wall cavities as shown with the blown fiberglass insulation in Figure 3, the blown cellulose in Figure 4, and the spray foam in Figure 5. It should be in substantial contact with the sheathing material on at least one side (interior or exterior) of the cavity.
- Faced batt insulation should be stapled to the surface of framing (Figure 6). Side-stapling is permitted, provided the tabs are stapled neatly (no buckling), the batt is only compressed at the edges of each cavity to the depth of the tab itself, and the batt meets the other requirements of Grade I.
Install slab edge insulation for slab-on-grade floors if the floor surface is less than 12 inches below grade and if required by code in your climate zone. Slab insulation should extend to the top of the slab to provide a complete thermal break (Figure 7). If the insulation is installed between the exterior wall and the edge of the interior slab, the insulation may be cut at a 45-degree angle away from the exterior wall, allowing the poured slab concrete to cover and protect the top edge of the insulation.
Insulating the slab edge will keep the floor warmer and reduce the potential for condensation and elevated relative humidity by allowing the inside surface temperature of the slab perimeter to more closely track the home’s interior temperature. If the slab is monolithic with a grade beam (Figure 8), the insulation is installed on the exterior of the slab edge/grade beam and continues vertically to the bottom of the grade beam. Use insulation material that is appropriate for ground contact such as XPS, rigid fiberglass, or rigid rock wool and use insect controls appropriate for the region. The above-ground portion of the rigid foam should be protected from UV and impact damage with coated fiber cement board.
When the slab is independent from the perimeter foundation wall, insulation may be installed either on the exterior of the foundation wall or between the foundation wall and the slab (Figure 8), which provides more protection for the insulation from the elements. When the insulation is between the foundation wall and the slab, it forms a bond break and it should also extend horizontally under the slab either at the perimeter or under the entire slab.
- Where an insulated wall separates a garage, patio, porch, or other unconditioned space from the conditioned space of the house, install slab insulation to provide a thermal break between the conditioned and unconditioned slab. Where specific details cannot meet this ENERGY STAR Ver. 3, Rev 6. requirement, provide the detail to EPA to request an exemption prior to the home’s qualification.
Home energy raters are required to inspect and probe in, around, or through the insulation and/or vapor retarder in several places to see whether insulation is installed to RESNET Grade 1 standards. . During inspection, insulation and vapor retarders may be cut or pulled away so raters can see installation details. The raters should replace or repair the vapor retarder and insulation as necessary. During inspection (typically before drywall is installed), if the exterior sheathing is visible from the building interior through gaps in the cavity insulation material, it is not considered a Grade I installation.
The amounts of insulation that must be installed in various building components are specified by code and vary by climate. The U.S. Department of Energy Building Energy Code Program identifies the building codes currently in force for each state.
For more information on the insulation levels required in the 2009 and 2012 International Energy Conservation Code (IECC), which are specified by climate zone, see the 2009 and 2012 IECC Code Level Insulation–ENERGY STAR Requirements and 2015 IECC Code Level Insulation – DOE Zero Energy Ready Home Requirements.
The map in Figure 1 shows the climate zones for states that have adopted energy codes equivalent to the International Energy Conservation Code (IECC) 2009, 12, 15, and 18. The map in Figure 2 shows the climate zones for states that have adopted energy codes equivalent to the IECC 2021. Climate zone-specific requirements specified in the IECC are shown in the Compliance Tab of this guide.
The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.
Rater Field Checklist
Thermal Enclosure System.
1. High-Performance Fenestration & Insulation.
1.3 All insulation achieves Grade I install. per ANSI / RESNET / ICC Std. 301. Alternatives in Footnote 4.4, 5
Footnote 4) Two alternatives are provided: a) Grade II cavity insulation is permitted to be used for assemblies that contain a layer of continuous, air impermeable insulation ≥ R-3 in Climate Zones 1 to 4, ≥ R-5 in Climate Zones 5 to 8; b) Grade II batts are permitted to be used in floors if they fill the full depth of the floor cavity, even when compression occurs due to excess insulation, as long as the R-value of the batts has been appropriately assessed based on manufacturer guidance and the only defect preventing the insulation from achieving Grade I is the compression caused by the excess insulation.
Footnote 5) Ensure compliance with this requirement using the version of ANSI / RESNET / ICC Std. 301 utilized by RESNET for HERS ratings.
Please see the ENERGY STAR Certified Homes Implementation Timeline for the program version and revision currently applicable in in your state.
Exhibit 1 Mandatory Requirements.
Exhibit 1, Item 1) Certified under the ENERGY STAR Qualified Homes Program or the ENERGY STAR Multifamily New Construction Program.
Exhibit 2 DOE Zero Energy Ready Home Target Home.
The U.S. Department of Energy’s Zero Energy Ready Home program allows builders to choose a prescriptive or performance path. The DOE Zero Energy Ready Home prescriptive path requires builders to meet or exceed the minimum HVAC efficiencies listed in Exhibit 2 of the National Program Requirements (Rev 07), as shown below. The DOE Zero Energy Ready Home performance path allows builders to select a custom combination of measures for each home that is equivalent in performance to the minimum HERS index of a modeled target home that meets the requirements of Exhibit 2 as well as the mandatory requirements of Zero Energy Ready Home Exhibit 1.
Exhibit 2, Insulation and Infiltration) Insulation levels shall meet the 2015 IECC and achieve Grade 1 installation, per RESNET standards.
Footnote 9) DOE Zero Energy Ready Home requires projects to be certified under the ENERGY STAR Certified Homes program or under the ENERGY STAR Multifamily New Construction (ESMFNC) program. Projects certifying under the ESMFNC program are advised that DOE ZERH certification requires that such projects use either the HERS or Prescriptive paths within the ESMFNC program, and that such projects are limited to 5 stories above grade or less to be eligible for DOE ZERH certification. Partners are also advised that DOE is developing a revised program design for multifamily dwellings, consistent with the ENERGY STAR Multifamily New Construction program, which will be available for use (but not yet required) on/after March 1, 2020. This program design is likely to be limited to buildings 5 stories above grade or less. Project certification under the ENERGY STAR Multifamily High-Rise program is not accepted at this time.
Sampling of those requirements for ENERGY STAR Homes qualification is permitted consistent with the ENERGY STAR for Homes V3 allowances for sampling (see ENERGY STAR Homes National Program Requirements). Sampling for Indoor airPLUS qualification is permitted consistent with the Indoor airPLUS program requirements.
With respect to Provision 1.3 within the ENERGY STAR Qualified Homes, Version 3/3.1 (REV09) Rater Field Checklist requiring RESNET-defined Grade I installation of insulation, where ceiling, wall, or floor assembly insulation is installed "blind" between layers of sheathing and therefore cannot be visually inspected, such assemblies are deemed equivalent to a RESNET-defined Grade I installation if the assembly insulation level is at least 50% greater than the specified value for the DOE Zero Energy Ready Home Target Home, based on nominal R-value.
Footnote 13) Insulation levels in a home shall meet or exceed the component insulation requirements in the 2015 International Energy Conservation Code (IECC) – Table R402.1.2. The following exceptions apply:
a. Steel-frame ceilings, walls, and floors shall meet the insulation requirements of the 2015 IECC – Table 402.2.6.
b. 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;
c. 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 sq. ft. or 20% of the total insulated ceiling area, whichever is less. This exemption shall not apply if the alternative calculations in d) are used;
d. An alternative equivalent U-factor or total UA calculation may also be used to demonstrate compliance, as follows: An assembly with a U-factor equal to or less than specified in Table 402.1.4 of the 2015 IECC complies. A total building thermal envelope UA that is less than or equal to the total UA resulting from the U-factors in Table 402.1.4 also complies. The insulation levels of fenestration, ceilings, walls, floors, and slabs can be traded off using the UA approach under both the Prescriptive and the Performance Path. Also, note that while ceiling and slab insulation can be included in trade-off calculations, Items 3.1 through 3.3 of the ENERGY STAR Rev09 Rater Field Checklist shall be met 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.
Section R303.1.1 Install insulation that has R-value marked on it or provide a certification listing the type, manufacturer, and R value of insulation installed in each element of the building envelope.
Section R303.1.1.1 For blown or sprayed in ceiling insulation the height of the insulation should be indicated on marker installed at least one for every 300 square feet in the space.
Section R303.2 Installation. All materials, systems, and equipment to be installed per the manufacturer’s instructions and the International Building Code or International Residential Code, as applicable.
Section R303.2.1 Insulation installed on exterior foundation walls should have a rigid, opaque, and weather-resistant covering that covers the exposed insulation and extends 6 inches below grade to prevent degradation.
Section R101.4.3 (Section R501.1.1 in 2015, 2018, and 2021 IECC). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)
Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.
The following authors and organizations contributed to the content in this Guide.
Poorly installed insulation can result in higher heating and cooling costs, comfort problems, mold and other moisture problems. Professionally-installed insulation meets industry best practices as specified for Grade 1 installation by the Residential Energy Services Network (RESNET). This includes no gaps, voids, compression, or misalignment with air barriers; complete air barriers; and minimal thermal bridging. This creates conditioned spaces that require very little heating and cooling, along with even comfort and quiet throughout the house.