The upgrade federal researchers put first

In November 2017, NREL published Residential Energy Efficiency Potential: Minnesota, built on its ResStock model of the nation's single-family housing. The upgrade at the top of Minnesota's list was not a smart thermostat, a replacement heating system, or new windows. It was R-10 basement wall insulation.

The model specified rigid foam installed on the inside of the foundation walls and rim joists—the location Commerce’s guide cautions homeowners about. The energy model did not establish moisture safety for an individual basement.

What the ranking means: NREL estimated economic potential from the homeowner's point of view, assuming broad adoption, using circa-2012 housing data. It shows the size of the statewide opportunity. It does not promise the same savings or the fastest payback in every house.

"Usually not a good idea"

The Minnesota Department of Commerce's Home Energy Guide: Basement Insulation says it plainly:

From the inside—usually not a good idea.

The guide says that unless moisture risk is very low, homeowners should leave interior basement walls uninsulated. It calls exterior insulation the best way, though it says that approach is usually more costly in an existing home.

For most existing homes, exterior insulation means digging around the foundation, past porches, steps, walks, landscaping, and utility lines. The state's caution about moisture is real. Basements can leak, and older methods failed. The same guide rejects the wood-stud-and-fiberglass walls that once trapped moisture against concrete.

Established building-science guidance describes safer interior approaches. Building Science Corporation and the Department of Energy's Standard Work Specifications describe interior assemblies that use continuous, moisture-tolerant rigid foam, water management, and sealed edges. These methods are designed to keep indoor air off cold masonry and to let the wall dry.

The $1,200 rebate that wasn't

On January 29, 2024, Xcel Energy filed its 2024–2026 ECO Triennial Plan. On printed page 87, the residential insulation program covers attic insulation, wall cavity insulation, and air sealing. It excludes basements and other below-grade installations, and it requires a registered contractor.

This case involves Green Home Club’s own founder, John Horchner. He spent more than $100,000 on energy improvements to his Saint Paul home, including continuous rigid foam on the basement walls, and received $400 in rebates. In his public comment, Horchner reports that Xcel denied his application for a further $1,200 insulation rebate, citing the basement exclusion and its registered-contractor requirement. The comment also recounts Commerce’s response defending the contractor requirement on training, quality-assurance, and moisture-protection grounds.

The result is three positions that don't line up:

1. Federal modeling ranks basement wall insulation first for statewide bill-savings potential.
2. State guidance discourages doing it from the inside.
3. Xcel’s residential insulation program excludes basement work entirely.

The rebate account is drawn from Green Home Club's public comment in PUC Docket 26-341.

An audit is a beginning. Sometimes it’s also the end.

CEE’s March 2026 Hennepin County action plan estimates current delivery at roughly one-tenth to one-quarter of the pace its model requires. CEE notes that differences in program reporting prevent an exact count.

In a 2018 Wilder Research evaluation for CenterPoint Energy and CEE, 56% of respondents answering the completion question—164 of 292—reported completing none of three recommended envelope upgrades: attic insulation, attic air sealing, and wall insulation.

Among respondents with no plans to finish their remaining recommendations, competing home improvements and inability to afford the expense were the leading main barriers. Interviews also identified work that had to happen first, including ventilation improvements and addressing knob-and-tube wiring.

There was progress, too: 44% completed at least one recommended upgrade.

These were self-reported pilot results, not a statewide completion rate or proof that rebate exclusions caused the unfinished work. The survey received 300 responses from 970 invitations (31%); eight respondents did not provide a usable completion answer. Of the 164 reporting no completed upgrades, 98 were still considering the work or unsure about future plans. “Not completed” described the time of the survey, not necessarily a permanent decision. The study did not report a separate basement-insulation completion rate. See Wilder, pp. 2–5, 8–9, 14–15, 24–25, and 27.

On October 15, 2026, Green Home Club filed a public comment in the Minnesota Public Utilities Commission's affordability investigation, Docket 26-341. The comment asks why the gap between assessments and finished work is so large, and why an upgrade with substantial modeled savings potential is excluded from program rules.

Other cold states found a way

Other programs show that quality safeguards and foundation incentives can exist together.