MUBEC: Maine's Building & Energy Code

What MUBEC is

The Maine Uniform Building and Energy Code (MUBEC) is the statewide building and energy code adopted and maintained by Maine's Technical Building Codes and Standards Board. It's assembled from several national model codes and standards — the International Code Council's building, residential, and energy codes, plus referenced ASHRAE and ASTM standards — amended and adopted as a single, uniform set of rules for construction across Maine. The energy-focused portion of MUBEC, sometimes called the Maine Uniform Energy Code (MUEC), is what sets insulation, air-sealing, and mechanical-efficiency requirements for new buildings.

Where it applies — and where it doesn't

MUBEC applies statewide, but enforcement responsibility depends on population: municipalities with more than 4,000 residents are required to enforce it, while smaller towns may choose to enforce it or not. Where a small municipality does enforce a building code, state law requires it to be MUBEC in full, rather than a locally written alternative — the goal is one uniform code, not hundreds of local variations. A narrow exemption exists for small, owner-occupied seasonal dwellings under 750 square feet with no central heating system, a limited electrical service, and no year-round wastewater system.

Current code edition

As of April 7, 2025, MUBEC's energy provisions are based on the 2021 International Energy Conservation Code (IECC), replacing the previous 2015 IECC edition that had been in effect since July 1, 2021. The 2021 edition raised several residential insulation targets compared to the code it replaced — most notably the prescriptive ceiling insulation level, which increased from R-49 to R-60 across Maine's climate zones. Maine law requires the Technical Building Codes and Standards Board to keep MUBEC within one edition of the most current model code, so further updates are expected on a multi-year cycle as the ICC releases new editions.

Maine's two IECC climate zones

The federal climate zone map that MUBEC's energy code is built around splits Maine into two zones, defined at the county level:

• IECC Climate Zone 7 — Aroostook County only. The coldest, most demanding zone in Maine's code.
• IECC Climate Zone 6 — all 15 other Maine counties, from York and Cumberland in the south to Washington and Penobscot in the east and north-central part of the state.

Zone 7 carries a higher prescriptive floor-insulation requirement than Zone 6, reflecting Aroostook County's more severe winter design temperatures. See the insulation regions page for a more practical, ground-level breakdown of how conditions vary even within Zone 6.

MUBEC / 2021 IECC prescriptive insulation table

*An exception permits R-49 where full-depth, uncompressed insulation extends over the wall top plate at the eaves — the code's way of allowing a slightly lower rated R-value where a raised-heel truss isn't used, provided depth isn't compromised at the perimeter. “ci” = continuous insulation, uninterrupted by framing. First number in a wall value is cavity insulation; second is continuous insulation.

Airtightness requirement

Alongside insulation levels, the energy code sets a maximum air leakage rate for new construction in Maine's climate zones: 3 ACH50 (air changes per hour at 50 Pascals), verified by a blower door test performed by the builder or a qualified third party and documented for the code official. This is the same test and the same metric described on this site's blower door testing page — MUBEC is simply the specific numeric target new construction has to hit.

The optional MUBEC Stretch Code

Beyond the base MUBEC requirements, the Technical Building Codes and Standards Board also maintains an optional MUBEC Stretch Code (Appendix NA) — a more stringent energy standard that individual municipalities can choose to adopt in place of the base code. Portland, South Portland, and Freeport have adopted stretch-code requirements ahead of most of the state. A municipality can't enforce a building code other than MUBEC, but it can choose to enforce MUBEC's stretch-code appendix instead of the base energy provisions.

Does MUBEC apply to my mobile home?

This is worth stating plainly: manufactured homes (the federally regulated category that includes most single-wide and double-wide “mobile homes”) are built to a national standard — the HUD Manufactured Home Construction and Safety Standards, 24 CFR Part 3280 — administered by the U.S. Department of Housing and Urban Development, not to MUBEC or the IECC. States are generally preempted from applying their own building energy code directly to the manufactured home itself. So MUBEC's insulation table isn't literally the legal standard a decades-old manufactured home was built to, or is required to be retrofitted to today.

Where MUBEC does become directly relevant is site-built work attached to or around a manufactured home — a stick-built addition, an attached garage, or a foundation and site-built enclosure — which is regulated as ordinary construction. And even where it isn't the legal requirement, the MUBEC/IECC table above is the best available, climate-specific reference point for what “well insulated for Maine” actually means. That's why this site uses it as the retrofit target throughout the R-value and insulation upgrade pages, even for homes the code doesn't technically govern.