Maine’s construction industry is undergoing a major transformation with the implementation of the 2021 MUBEC Code. This statewide update is reshaping how homes are built, raising the bar on insulation, ventilation, air sealing, and overall energy performance. Whether you’re a seasoned contractor, an architect designing your next project, or a homeowner planning a new build, these changes will impact both your approach and your budget.
One of the most talked-about updates? The shift from R-49 attic insulation to R-60 attic insulation. It’s a big jump that significantly reduces heat loss and slashes winter heating bills. Alongside that, builders are now expected to integrate rigid foam insulation and continuous insulation (CI walls) into exterior walls, improving efficiency and eliminating cold spots.
With heating costs still high and climate goals front and center, the focus on energy-efficient construction has never been stronger. Compliance is no longer optional. The new code mandates stricter testing and documentation, pushing everyone to get serious about Maine energy code compliance. This is more than a rule change—it’s the new normal for Maine’s 2025 building market.
Understanding the 2021 MUBEC Code
To understand how Maine’s construction landscape is evolving, it’s important to grasp the foundation of the 2021 MUBEC Code. This section breaks down what the code is, why it matters, and what specific changes are shaping the way homes are being built and upgraded in 2025.
What is MUBEC?
MUBEC, short for the Maine Uniform Building and Energy Code, is the set of baseline construction and energy efficiency rules that govern residential and commercial building projects throughout the state. As of April 2025, Maine updated its code to align with the 2021 International Energy Conservation Code (IECC)—a move that reflects the state’s increasing commitment to reducing energy waste and building smarter, more durable homes.
Key Code Changes
Several critical updates are now in effect under the 2021 MUBEC Code:
- Attic Insulation: Minimum raised from R-49 attic insulation to R-60 attic insulation to reduce heat loss and improve winter energy efficiency.
- Wall Assembly: Requirements now include continuous insulation with configurations like R-13 insulation + R-10 ci or R-20 insulation + R-5 ci.
- Air Sealing: Homes must pass blower door tests with air leakage ≤ 3 ACH50, ensuring tighter envelopes.
- Mechanical Ventilation: All homes must now include systems that meet IRC M1505 standards.
- Lighting: Only high-efficacy fixtures like LEDs and CFLs are allowed.
| Area | 2015 Standard | 2021 Standard | Why It Matters |
| Attic/Roof | R-49 | R-60 (Climate Zone 6) | Cuts winter heat loss by ±10 % and meets the IECC 2021 ceiling U-factor of 0.024 Topsham Maine |
| Walls | R-20 (or R-13 + 5 ci*) | R-20 + 5 ci • R-13 + 10 ci • R-30 cavity only | Continuous insulation (ci) combats thermal bridging |
| Air leakage | ≤ 3 ACH50 (but enforcement spotty) | Must test & hit ≤ 3 ACH50 statewide | Ensures the higher R-values actually perform |
| Ducts | R-6 (small) / R-8 (large) | Same R-values, but stricter sealing & burial rules | |
| Lighting | 75 % high-efficacy | 100 % high-efficacy (LED, CFL) | |
| Ventilation | Not always required | Mechanical ventilation per IRC M1505 |
- *ci = continuous insulation (rigid foam) on the exterior sheathing.
Why R-60 Is a Big Deal
Maine’s frigid winters make attic insulation R-60 a smart upgrade. In Climate Zone 6, this increase reduces winter heat loss by approximately 10%, which means lower heating bills and greater indoor comfort.
Hitting R-60 in Real Life
Builders can meet this requirement in a few ways:
- Blown-in cellulose or fiberglass: Requires around 18–19 inches of material.
- Spray foam with a cellulose top-off: Typically 5–7 inches of closed-cell foam under 12 inches of cellulose.
- Batts and blown-in combo: A retrofit-friendly method that layers R-38 batts with R-22 blown-in.
These assemblies come with added costs—roughly $0.30 to $0.50 per square foot more than previous standards. Raised-heel trusses may also be necessary to accommodate the extra depth. However, despite an average increase of $1,800 to $2,500 per home, homeowners typically recoup this investment within 4–7 years through energy savings.
Why the Code Matters in 2025
Understanding why the 2021 MUBEC Code is a game-changer for Maine’s housing market goes beyond memorizing new R-values or air-tightness numbers. This section explains the practical significance behind the code—how it’s being enforced, what it means for builders and homeowners, and why the upfront investment is worth the payoff.
Statewide Enforcement Gets Serious
Previously, air sealing was often encouraged but not consistently enforced. That changes in 2025. Every new home across the state must now pass a blower door test that demonstrates air leakage of 3 ACH50 or less. This is no longer a suggestion—it’s a requirement. And it ensures that all that high-value house insulation is actually effective, rather than being undermined by leaky gaps.
Impacts on New Construction and Retrofits
For new builds, the code prompts some design reconsiderations:
- Framing must accommodate R-60 attic insulation depth
- Walls require exterior rigid foam insulation to hit updated performance targets
- Mechanical ventilation must be built into every home
Retrofits face steeper challenges. Adding insulation and tightening older homes can be costly and complex. Still, bringing them up to code can yield big rewards in energy savings and comfort.
Costs vs. Long-Term Gains
Initial costs have risen—builders report an average of $1,800 to $2,500 in added construction expenses for a 2,000-square-foot home. But those costs are offset within a few years through reduced heating and cooling bills. Plus, code-compliant homes offer better resale value and long-term comfort thanks to energy-efficient construction.
How Builders and Developers Are Responding
Meeting the new demands of the 2021 MUBEC Code requires more than just reading the rulebook—builders and developers are evolving their methods, materials, and mindsets to stay ahead.
Material Innovations
To meet stricter energy performance targets, builders are turning to smarter material choices. Dense-pack cellulose and mineral wool are popular options for boosting R-values, especially in walls and attics. These materials are not only efficient but also cost-effective and readily available. For exterior walls, rigid foam insulation—like EPS, XPS, and Polyiso—is now frequently used to stop thermal bridging and increase overall envelope performance. In addition, air-sealing solutions such as advanced tapes, sealants, and gaskets are essential to hit the required airtightness levels.
Code Training and Upskilling
As expectations rise, so does the need for specialized skills. Today’s crews must know how to handle CI wall installation, execute accurate blower door tests, and seamlessly incorporate mechanical ventilation systems. These are no longer niche skills—they’re baseline requirements.
Design Changes
Architects and designers are getting proactive. Deeper attic framing, wider wall cavities, and tighter envelopes are now built into design plans from the start. REScheck software is often used in the planning phase to evaluate how different trade-offs affect overall compliance and performance.
Statewide Implications for Housing and Sustainability
The ripple effect of the 2021 MUBEC Code goes far beyond insulation and blower door tests—it’s reshaping how homes are designed, built, and financed across Maine. This section explores how the updated code affects housing affordability, environmental policy, and statewide support programs.
Affordable Housing and Compliance
For affordable housing developers, meeting the new performance standards is a major hurdle. Budget constraints are tight, yet compliance with R-60 attic insulation, ci walls, and blower door requirements is non-negotiable. To navigate this, many builders are relying on the REScheck path, using it to strategically trade higher performance in one area for more flexibility in another, like pairing R-21 insulation in walls with triple-pane windows. Additionally, prefab and modular construction are gaining traction as a solution. These systems arrive on-site already insulated, sealed, and compliant, saving both time and labor costs.
Energy Policy and Sustainability Goals
The 2021 MUBEC Code directly aligns with Maine’s larger climate objectives. By reducing thermal loads, the code makes homes more compatible with electric heating systems and lowers greenhouse gas emissions—a big step toward carbon reduction targets.
Efficiency Maine’s Role
Efficiency Maine plays a crucial role in supporting this transition. From builder training sessions to rebates on high-efficiency equipment, the program helps ensure that Maine energy code compliance is achievable and practical, not just an expensive mandate on paper.
Looking Ahead: What to Expect Beyond 2025
As Maine moves forward, the 2021 MUBEC Code won’t be the final stop for energy performance improvements. With the 2024 IECC already published, there’s growing anticipation that Maine’s next code update will push building standards even further.
Future Code Updates
Upcoming revisions may lower the air leakage target below 3 ACH50, requiring builders to take airtightness to the next level. Stricter U-factor requirements for windows and doors are expected, pushing product specs closer to passive house levels. Also gaining traction is the push for solar-ready homes and electrification infrastructure, like pre-wiring for EV chargers or heat pumps, making today’s builds more future-proof.
Prefabrication Takes the Lead
Modular construction is gaining momentum. Factory-built panels with continuous insulation, sealed joints, and integrated air barriers make code compliance faster and more predictable. This method also helps with labor shortages and quality control.
Modeling and Compliance Tech
REScheck and energy modeling software are becoming indispensable. Builders can no longer guess or eyeball compliance. These tools now guide early design choices, prevent costly oversights, and offer verification that designs meet or exceed Maine energy code compliance requirements.
Adapting to a More Efficient Future
The 2021 MUBEC Code is reshaping how homes are designed, built, and lived in throughout Maine. From R-60 attic insulation to ci walls, it’s all about better performance and long-term value. Builders who embrace the code will lead the market—those who ignore it will fall behind.
Homeowners, too, benefit from tighter envelopes and lower energy bills. With the help of tools like REScheck and programs like Efficiency Maine, staying compliant doesn’t have to be a headache.
Contact us today to explore your options for Maine energy code compliance, third-party energy audits, or project planning assistance. Let’s build a smarter, warmer, and more efficient Maine together.