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Basement Wall Insulation

Installed correctly, basement wall insulation can cut your utility bills, make your home more comfortable, and increase its value.

Older homes without effective basement wall insulation allow excessive heat loss in winter and heat gain in summer. Insulating walls is a highly effective way to improve your home’s performance. It can reduce your heating and cooling bills, improve comfort with less drafts, and help your home meet increasing performance expectations. The optimum location for basement wall insulation is on the exterior; however, this is typically impractical for existing homes. The following options are available for insulating from the inside. For exposed foundation walls, spray foam or rigid foam panels can be applied directly or a framed assembly can be constructed then filled with batt or blown-in insulation and finished with drywall. For finished basements, holes can be drilled and insulation blown into the framing cavities.

Checklist

This U.S. Department of Energy checklist includes important specifications that can contribute to a complete and quality installation. All work shall comply with these specifications, all relevant codes and standards, and all manufacturer installation instructions. The contractor shall check each box on the checklist below and sign and date at the bottom to certify the work is completed.

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Preparation


The basement shall be inspected for any evidence of asbestos, lead paint, bulk water penetration, moisture, or pest damage, and a list of any potential problems shall be provided to the homeowner before proceeding with the work so remediation can be fully addressed as necessary.

Doors from the basement to the outside shall be replaced with minimum R-5 insulated doors that are fully weather-stripped.

A continuous sealant (e.g., caulk, foam, or aerosol sealant) compatible with its intended surfaces and maximum gap dimensions shall be applied to all exposed rim joist and foundation wall cracks, seams, or holes including where the foundation meets the sill plate, where the sill plate meets the rim joist, and where the rim joist meets the subfloor.

Option 1: Unfinished Basement Insulation


All rim joists adjoining the exterior shall be insulated directly against the rim joist with closed-cell spray foam and/or rigid insulation board to an R-value that meets or exceeds the prescriptive levels specified by the 2012 International Energy Conservation Code for the home’s location. If only rigid insulation board is used, seams shall be fully sealed with caulk, foam, mastic, or flashing tape specified acceptable by the rigid insulation manufacturer.

Basement walls shall be insulated with either spray foam or rigid foam insulation panels.

If using spray foam, a steel or treated-wood stud wall shall be constructed 2 inches away from the basement wall. (The space allows complete coverage of the wall and reduces thermal bridging.) High-density closed-cell or medium-density open-cell foam shall be sprayed directly on the entire surface of all basement walls adjoining the exterior.

Any exposed non-fire-rated spray foam or rigid foam insulation shall be covered with a code-approved ignition barrier or a fire-rated assembly such as 1⁄2-inch drywall.

If drywall is installed, it shall be at least 1⁄2 inch off the floor to help protect against potential moisture problems.

If using rigid foam insulation panels, they shall be attached to the interior of the basement wall with construction adhesive applied in a serpentine pattern. When using two layers of foam, stagger the seams. These panels shall completely cover all basement wall surfaces exposed to the exterior with no air gap between them and shall be fully in contact with the masonry wall, with no gaps. Panel seams shall be fully sealed with caulk, foam, mastic, or flashing tape specified as acceptable by the rigid foam manufacturer.

If using rigid foam insulation panels, furring strips shall be installed to create a nailing surface for the drywall.

Option 2: Finished Basement Insulation


If the basement walls are already covered with framing and insulation, inspect the cavity walls for moisture. If no evidence of moisture is found, the walls can be left as is. If evidence of moisture is found, or if higher insulation levels are desired, remove the existing cavity wall, remediate any sources of moisture, then insulate the walls with spray foam or rigid foam and install a new insulated frame wall if desired..

The walls shall be insulated with spray foam or rigid foam with an R-value that meets or exceeds the prescriptive levels specified by the 2012 International Energy Conservation Code for the home’s location.

A new insulated frame wall shall be installed.

Commissioning


A combustion safety test in accordance with ANSI/ACCA 12 QH Appendix A or RESNET Chapter 8 shall be performed if any natural draft combustion equipment (e.g., water heater, furnace) exists in the basement to help ensure there is no back-drafting or spillage of combustion emissions. Recommendations for remediation shall be made to the homeowner where combustion safety issues are identified.

At the completion of the work, a radon test kit shall be provided to the homeowner to measure post-retrofit radon levels and implement a remediation strategy if radon levels exceed EPA limits.
Basement Wall Insulation

Tips to Sell Quality Installed Home Improvements

Home Improvement Expert is a valuable tool for organizations committed to quality installed work. The following tips help optimize the value of this tool when selling home improvements:

Trust Matters: Inform homeowners how your work conforms to this world-class expert guidance. Recommend they visit the DOE website as evidence these are indeed official best practices.

Knowledge Matters: Take advantage of the Building America Solution Center as a resource for becoming an expert on these projects.

Clarity Matters: Tell prospective clients to contrast your expert-recommended best practices with other contractors.

Value Matters: Advise prospective clients to insist other bids also include these checklists to ensure equivalent quality work.

Message Matters: Showcase on your website and marketing materials that your company uses the highest quality best practices specified on HIE Checklists.

Experiences Matter: Provide visual evidence contrasting the difference between poor and high quality work such as infrared images; pre- and post-energy bills; short and long warranties; and simple charts and graphics depicting performance advantages.

Related Guides

Guide:

Pre-Retrofit Assessment of Crawlspaces and Basements

Description
Information guide describing things to consider when considering home retrofits in the basement or crawlspace including HVAC, wiring, or structural systems.
Guide:

Air Sealed, Insulated Basements

Description
Guide describing how to insulate a basement to improve the overall thermal performance of the building and provide more dry, usable conditioned space for home occupants and HVAC equipment.
Guide:

Floor Above Unconditioned Basement or Vented Crawlspace

Description
Guide describing how to air-seal and insulate the floor above an unconditioned basement or crawl space.
Guide:

Water Management of Existing Basement Floor

Description
Guide describing how to retrofit an existing basement floor or slab to reduce moisture issues.

Disclaimer

This content is a work created with funding provided by the United States Department of Energy under Contract no DE-AC05-076RL01830 for the operation of Pacific Northwest National Laboratory. The information and guidance provided by Pacific Northwest National Laboratory (PNNL) in the content are intended solely for educational purposes only and do not constitute formal training or certification. It is provided with the explicit understanding that neither the United States Government nor the United States Department of Energy, nor the Contractor, nor any or their employees, nor any jurisdiction or organization that has cooperated in the development of these materials, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness or any information, apparatus, product, software, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or Battelle Memorial Institute. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Viewers assumes full responsibility for all actions that they may take from information provided in this content including ensuring the safety, code compliance, and proper functionality of any products they choose to install. Installation and use of such products should be performed in accordance with local regulations and manufacturer instructions.