By Dan Kolbert

THIS COLUMN’S NUMBER IS A YEAR. It represents a step both back and forward in time. The year is 2015. Specifically, the 2015 International Energy Conservation Code (IECC). This is the energy code recently adopted by the state of Maine, replacing the 2009 version that was in force through June 30 of this year (the 2015 IECC became effective on July 1). There are already 2018 and 2021 versions, but Maine has, unfortunately, chosen the “go slow” route. And, even though it is still two versions behind, the 2015 version is still a step forward from the 2009 code.

Let’s take a look at some of the major changes. Much of the information here comes from my interview of Claire Betze of BuildingWorks in Freeport. She is a Home Energy Rating System (HERS) rater, a Building Performance Institute (BPI)-certified building analyst, and an energy consultant on residential projects. She is also involved in the Maine Energy Codes Collaborative, a group of stakeholders working to support and promote adoption of the updated energy code.

The IECC sets out different minimum standards for different climate zones (CZ). The United States goes from CZ 1 in southernmost Florida, Hawaii and other similar climates, to CZ 7 in the upper Midwest and the Rockies. Maine is in CZ 6, except for Aroostook County, which is CZ 7. I will be referring to CZ 6 standards here; the ones for CZ 7 are slightly higher.

WALLS

The 2009 code says walls have to have an R-value of 20 or greater if insulation is just in the wall cavity or can go to R-13 in the cavity if there is R-5 of “continuous” insulation (13+5). This acknowledges that the thermal break provided by continuous insulation greatly improves the performance of a framed assembly. The continuous layer, typically provided by a layer of rigid foam on the exterior or a product like Huber’s ZIP System® R-sheathing (rigid foam adhered to the inside of their ubiquitous green ZIP sheathing), could also be the space in a double-wall system, filled with cellulose or other blown-in insulation.

These values go up in the 2015 code and make continuous insulation mandatory. The wall requirements will now be R-13 in the cavity + R-10 of continuous or R-20 cavity + R-5 continuous. Betze says she is worried that the second option “will get people in trouble.” That’s because most builders achieve continuous insulation by putting rigid foam board over the sheathing (the plywood attached to the exterior of the studs). This can help protect the sheathing by keeping it warm and thus not a surface where water will condense in cold weather. However, in CZ 6 and CZ 7, R-5 on the exterior won’t keep the sheathing warm enough. And because the foam typically used is not vapor permeable, that condensate can’t escape easily and can cause rot.

Building Science Corporation, an internationally recognized consulting and research group, recommends that 35%, or roughly one-third, of the total R-value be on the exterior if using rigid foam over the sheathing. It’s important to remember that the code requirements are minimums, and nothing prevents you from going as far over them as you want. So, following the Building Science Corp. recommendations, if you’re going to use R-20 in the walls, you should have at least R-11.25 on the exterior.

Most builders concerned with energy efficiency would recommend far higher R-values; generally R-40 for walls, following the guidance from Building Science Corp. and the Pretty Good House model, a building science-based model that got its start here in Maine and seeks to strike a balance between price and performance.

AIRTIGHTNESS

Another big change is in airtightness. The 2009 IECC mandated an airtightness level of 7 air changes per hour at 50 pascals of pressure (ACH 50), and did not require a blower door test to confirm the number (see my column 1 ACH 50 for an explanation of ACH 50 and blower door tests). This threshold was absurdly high—a new house simply should not be anywhere near that drafty. And the lack of verification requirements probably meant many houses were even worse than that.

The 2015 IECC brings the number down to 3 ACH 50. While still higher than a conscientious builder would want to be, that’s not terrible. And more significantly, blower door tests are now mandated. Anyone, even the contractors themselves, can perform the test, but it must be done. Most builders have a “Eureka” moment at their first blower door test, seeing where the leaks are and how to plug them; the educational value alone should help raise the bar.

VENTILATION

Another new mandate is for ventilation systems. The more we learn about indoor air quality (IAQ), the more we realize how critical a reliable supply of fresh air is (see Michael Maine’s Building Science 101: Ventilation in for more on the subject). The code allows either an exhaust-only system (usually bathroom fans running constantly at low speed) or a balanced system—usually a heat-recovery ventilator (HRV) or energy-recovery ventilator (ERV)—but it must meet the 2016 version of the ASHRAE 62.2 standard for fresh air.

Enforcement will be critical, and that has traditionally been a weak point in Maine. Also, just as with the earlier versions of the code, towns of fewer than 4,000 people may choose not to enforce the code. There are only about three dozen municipalities in the state above that number, with Lisbon Falls the smallest at 4,019. Hopefully, Rumford (3,672) and the rest will realize the importance of the energy code and adopt it.

ENERGY RATING INDEX

Another piece that Betze says the new code adds is the Energy Rating Index (ERI). This is in addition to the UA Alternative or Performance paths, which were also available in the 2009 code but not used all that much. Like the HERS rating, the ERI is supposed to give a more objective way for a consumer to gauge a home’s energy efficiency. The lower the number, the more efficient the house, with 0 representing a Net Zero home. The new code’s threshold for our climate zone is a score of 54 or lower (with 100 being a code-minimum house meeting the 2006 energy code). The ERI path must use a third-party evaluator, but the UA Alternative can be used by anyone using simple calculations or RESCheck, which can be downloaded for free at energycodes.gov/rescheck.

As you can imagine, there is plenty more in the hundreds of pages of code. Windows and skylight performance has to be about 10% better. Crawl space insulation requirements are higher. Ducts are required to be twice as airtight. There are also several appendices that address important items such as combustion safety testing—such as making sure combustion appliances won’t backdraft—and planning for photovoltaic panels in roof orientation.

While it is disappointing that Maine did not choose to adopt the most recent code, the 2015 IECC is still a significant step forward. And the bureau that oversees the Maine Uniform Building and Energy Code (MUBEC) is in the process of moving forward with adopting 2021 IECC as a “stretch” code that several towns, such as Portland and South Portland, are eagerly looking forward to adopting.

This article appeared in the Fall 2021 edition of Green & Healthy Maine HOMES. Subscribe today!

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