Does a window off the shelf at a home center meet Maine's code?

Read the NFRC label, not the sticker. The code asks for a U-factor of 0.30 or lower, and the label prints the window's own figure; an ENERGY STAR window for the Northern zone, at U-0.22 or lower, clears it easily.

Why does ENERGY STAR want a high SHGC in Maine?

Because heating is the big bill here. A higher solar heat gain coefficient lets winter sun warm the room, so the Northern zone sets a minimum SHGC instead of the maximum used in hot climates.

Does the code apply in a small town that does not enforce it?

Yes. Maine's code rule says the code applies to all buildings constructed or renovated in Maine regardless of town size; a small town simply does not inspect for it.

Maine window energy code, Portland area

An energy code puts two numbers on a window. The U-factor is how fast heat leaks through it: lower is better, and in a Maine winter it is the number that matters. The solar heat gain coefficient (SHGC) is how much of the sun's heat it lets in. Across the 64 towns we cover there is one answer to what a replacement window must meet, because the state sets it.

What each town requires

Requirement	Towns	Which ones
U-0.30 or lower	64	Acton, Alfred, Arrowsic, Arundel, Baldwin, Bath, Berwick, Biddeford, Bowdoin, Bowdoinham, Bridgton, Brunswick, Buxton, Cape Elizabeth, Casco, Cornish, Cumberland, Dayton, Eliot, Falmouth, Freeport, Georgetown, Gorham, Gray, Harpswell, Harrison, Hollis, Kennebunk, Kennebunkport, Kittery, Lebanon, Limerick, Limington, Lyman, Naples, New Gloucester, Newfield, North Berwick, North Yarmouth, Ogunquit, Old Orchard Beach, Parsonsfield, Phippsburg, Portland, Pownal, Raymond, Richmond, Saco, Sanford, Scarborough, Sebago, Shapleigh, South Berwick, South Portland, Standish, Topsham, Waterboro, Wells, West Bath, Westbrook, Windham, Woolwich, Yarmouth, York

One code for the state

The Maine Uniform Building and Energy Code adopts the 2021 International Energy Conservation Code for the whole state, in force since April 7, 2025. Maine's own changes touch wall insulation, air leakage and basement bulkheads, and leave the window figure alone. A town of more than 4,000 residents must enforce it; a smaller town may choose not to, but may not adopt any other code, and the state says meeting it is the building owner's responsibility either way. Cumberland, Sagadahoc and York counties are all IECC climate zone 6A, cold and moist, on the 2021 map Maine's code uses, and none of them changed zone from the earlier maps.

What each edition set

Edition	Max window U-factor	Max SHGC
2009 IECC	U-0.35	None
2015 IECC	U-0.32	None
2021 IECC	U-0.30	None

Climate zone 6 figures. Maine's statewide code used the 2015 edition until the 2021 edition took over on April 7, 2025; no edition sets an SHGC limit in zone 6.

Does the code reach a replacement window?

Yes, when the window itself is replaced. When an existing window is replaced with a new one, the new unit has to meet the code's U-factor; a storm window added over an old window is not a replacement window. (IECC section R503.1.1.1, Replacement fenestration (2021 edition)) Kennebunk's code office puts it in one line: replacement windows and doors need a permit because the state's energy code requires them to meet current standards.

The stretch code

A town may also adopt the state's stretch code, which asks a new project's whole envelope to beat the code by 15 percent, or 10 percent in an all-electric house; it is measured on the whole building, not as a separate window figure. Portland adopted it by referendum, and South Portland lists the 2021 energy code as its own stretch code. Neither changes the figure on a single replacement window.

The figure worth buying to

All three counties are in ENERGY STAR's Northern window zone, checked county by county on ENERGY STAR's own lookup. A window qualifies there at a U-factor of 0.22 or lower with an SHGC of 0.17 or higher; slightly less insulating windows qualify only with more solar gain (U-0.23 or 0.24 with an SHGC of 0.35 or higher, or U-0.25 or 0.26 with an SHGC of 0.40 or higher). The SHGC is a floor here, not a ceiling, because winter sun through south and west windows is free heat. The Most Efficient tier asks for U-0.20 or lower. Every one of those clears the code's U-0.30 by a wide margin.

Where this comes into the work

Sources: maine.gov · legislature.maine.gov · maine.gov · maine.gov · basc.pnnl.gov · durhammaine.gov · hub.utahcleanenergy.org · maine.gov · energystar.gov · energystar.gov · energystar.gov · energystar.gov · osti.gov · kennebunkmaine.us

What a replacement window has to meet in Maine