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Code Compliance

We install to code.Here is exactly what that means.

Minnesota's residential energy code sets minimum R-values by assembly and by climate zone, and adds specific fire and moisture rules for foam plastic insulation. This page lays out those requirements in plain English, with every figure linked back to the official source, so you know exactly what your project is required to meet, and what to expect from a contractor who takes that requirement seriously.

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The Governing Code

Minnesota's Residential Energy Code.

Minnesota's insulation requirements live in Minnesota Rules Chapter 1322, the Residential Energy Code. That chapter adopts the 2012 International Energy Conservation Code as its base and layers Minnesota's own amendments on top of it, several of them stricter than the national baseline to account for our winters. It has been the enforced code since February 2015.

The Department of Labor and Industry has opened an early rulemaking process, with a request for comments published in February 2026, that proposes moving the residential energy code forward to reference the 2024 International Residential Code's energy chapter. As of this writing that process has no adopted rule, no hearing date, and no effective date, so the 2012 IECC-based code described on this page remains the one your project is actually built and inspected against.

Sources: Minn. R. 1322.0010, MN DLI 2020 Minnesota Residential Energy Code fact sheet, and MN DLI rulemaking docket, Chapter 1322.

Find Your Zone

Minnesota sits in two climate zones.

The R-value table below is organized by federal climate zone, because the code asks more of colder ground. Minnesota is split between Zone 6 and the colder Zone 7.

Zone 7

Aitkin, Beltrami, Carlton, Cass, Clearwater, Cook, Crow Wing, Hubbard, Itasca, Kittson, Koochiching, Lake, Lake of the Woods, Mahnomen, Marshall, Norman, Pennington, Pine, Polk, Red Lake, Roseau, St. Louis, and Wadena counties.

Zone 6

Every other Minnesota county, including the entire Twin Cities metro and our home base in Savage.

Source: MN DLI Residential Energy Code Technical Advisory Group handout, aligning the residential code's county assignments with the climate zones already adopted for Minnesota's Commercial Energy Code (Minn. R. 1323.0514).

Minimum R-Values

What the code requires, assembly by assembly.

These are minimums, not targets. A well-built project often exceeds them where it makes sense, but every number below is a floor your home has to clear at inspection.

Ceiling / Attic
Zone 6:R-49
Zone 7:R-49
Above-Grade Wood Frame Wall
Zone 6:R-20 cavity, or R-13 cavity + R-5 continuous
Zone 7:R-21 cavity
Floor Over Unconditioned Space

Applies to floors over garages, crawl spaces, and other unconditioned areas.

Zone 6:R-30, or fill the cavity (R-19 minimum)
Zone 7:R-38, or fill the cavity (R-19 minimum)
Basement Wall
Zone 6:R-15
Zone 7:R-15
Slab Edge
Zone 6:R-10, extending 3.5 ft below grade
Zone 7:R-10, extending 5 ft below grade
Crawl Space Wall
Zone 6:R-15
Zone 7:R-15
Rim Joist / Band Joist

Treated as part of the wall assembly in most editions of the code; confirm the current figure with your building official.

Zone 6:{{VERIFY: exact Minn. R. 1322 rim joist R-value citation}}
Zone 7:{{VERIFY: exact Minn. R. 1322 rim joist R-value citation}}

Source: Minn. R. 1322.0402, Table R402.1.1 (as amended). R-values are minimums under Minnesota's residential energy code. Local jurisdictions and individual site conditions can add requirements on top of these numbers, and code editions change over time, so always confirm the current requirement with your building official before a permit is pulled.

Spray Foam Rules

The requirements specific to foam plastic.

Meeting an R-value is only part of the code. Spray foam is a foam plastic insulation, and the building code adds fire-safety and moisture-control rules on top of the energy table above.

Thermal barrier. Under IRC Section R316.4, as adopted into the Minnesota Residential Code, foam plastic has to be separated from the occupied interior by an approved thermal barrier, typically half-inch gypsum wallboard, unless the assembly is tested to NFPA 275 instead.
Ignition barrier exceptions. Unoccupied attics and crawl spaces entered only for repairs or maintenance can use a lighter ignition barrier in place of the full thermal barrier, and masonry or concrete assemblies and certain roof assemblies have their own narrow exceptions.
Flame spread and smoke rating. Foam plastic itself has to test at a flame spread index of 75 or less and a smoke-developed index of 450 or less under ASTM E84, before any thermal barrier is even considered.
Vapor retarder. In Zones 6 and 7, the code calls for a Class I or Class II vapor retarder on the interior side of frame walls. Spray foam applied at the right permeance and thickness can meet this on its own in many wall assemblies, which is part of why it performs well here, but the specific assembly still has to be checked.

Sources: 2020 Minnesota Residential Code, Section R316, Foam Plastic and Section R702.7, Vapor Retarders.

Why It Matters

Why a code-aware, insured contractor is worth it.

Passes Inspection the First Time

Knowing the exact R-value and vapor-retarder requirement for your zone and assembly before the job starts means no surprises at inspection, and no rework.

Protects the Building, Not Just the Bill

Thermal barriers and vapor retarders exist because foam in the wrong assembly can create a fire risk or trap moisture. Following the code is how those risks stay off the table.

Fully Insured, Every Job

Trust Works Company carries insurance on every project, with 20+ years of hands-on experience insulating Minnesota homes and buildings to the code that actually governs them.

Common Questions

Frequently asked questions.

Minnesota's Residential Energy Code is Minnesota Rules Chapter 1322, which adopts the 2012 International Energy Conservation Code with Minnesota's own amendments layered on top. It has been in effect since February 2015 and remains the enforced code as of this writing. The Department of Labor and Industry is in the early stages of a rulemaking process to update it to reference the 2024 International Residential Code's energy chapter, but that update had not been adopted as of this writing.
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