December 19, 2014 | Ryan Meres

This blog post is the second of a two-part series for Builder Magazine on what the 2015 International Energy Conservation Code means for home builders.

Continuing our exploration of the 2015 International Energy Conservation Code (IECC), let’s take a look at what makes this latest version of the code different from the 2012 IECC. The biggest alteration that will affect builders is the addition of an Energy Rating Index compliance path, as discussed in our earlier blog post. However, that’s not the only change builders should note.

Five of the major adjustments in the 2015 IECC that will affect new home construction include specifying required inspections; revised requirements for vertical access doors; a new requirement for combustion closets; revisions to the building envelope air leakage testing requirements; and revised requirements for duct insulation.

To dig into these changes and many other small revisions, you can read a fact sheet my team created here. Below, however, are five key revisions to pay attention to:

1. Required inspections

Section 104 was revised to list and describe required inspections as:

  • Footing and foundation
  • Framing and rough-in
  • Plumbing rough-in
  • Mechanical rough-in

What’s the difference? The 2012 IECC simply says that “work shall not be done beyond the point indicated in each successive inspection without first obtaining the approval of the code official.” This provides no guidance or indication of which inspections are required. The new 2015 provisions, however, specify when the inspection should be done and what should be inspected.

Potential impact: Because many local jurisdictions delete Chapter 1 and reference their own administrative procedures, it’s possible that the impact of this change will be minimal, but it will be felt the most where a jurisdiction adopts the new inspection requirements. In those areas, builders will have to adapt to the change by not covering up the items that need to be looked at and requesting inspections at the appropriate times.

2. Vertical access doors

A new exception has been added to Section R402.2.4—“Access hatches and doors.” This exception allows vertical doors that provide access from conditioned to unconditioned spaces to meet the fenestration requirements in Table R402.1.2.

What’s the difference? This change means that these types of doors, such as attic kneewall doors and other vertical attic access doors, do not have to be insulated to the same level as the surrounding wall, as long as they meet the fenestration U-factor requirements specified in Table R402.1.2.

Potential impact: This change now allows the option of using an exterior door that meets the U-value requirements or an interior door with enough insulation attached to the back to meet the vertical access door requirement.

3. Building envelope air leakage testing

Building envelope air leakage testing must now be done in accordance with either ASTM E 779 or ASTM E 1827.

What’s the difference? In both the 2009 and 2012 versions of the IECC there were requirements for air leakage testing of the building envelope, but neither code referenced any standard by which to conduct the test. The 2015 code now requires that one of the two ASTM standards be followed when conducting the air leakage test.

Potential impact: The impact of this requirement is expected to be minimal, but make sure your air leakage testers know the ASTM standard.

4. Combustion closets

There is a new section, R402.4.4—“Rooms containing fuel burning appliances,” that states “where open combustion air ducts provide combustion air to open combustion fuel burning appliances, the appliance and combustion air opening shall be located outside the building thermal envelope or enclosed in a room, isolated from inside the thermal envelope.” This new requirement only applies in Climate Zones 3-8, but requires combustion closets to be insulated to levels not less than the basement wall R-value requirements in Table R402.1.2. The closet must also be air sealed and the door must be fully gasketed.

What’s the difference? This is an entirely new requirement.

Potential impact: Complying with this new requirement could cost a few hundred dollars, depending on your current construction practices. There are several options for complying: (1) Install direct vent appliances (i.e., high-efficient furnace and water heater) where both intake and exhaust pipes are continuous to the outside; (2) Where you have combustion air ducts (often called hi/low vents) bringing combustion air to an atmospherically vented appliance, you can enclose the appliance in a combustion closet; (3) Don’t use combustion appliances (i.e., build an all-electric house); or (4) Locate your combustion appliances outside the building thermal envelope (i.e., in an unfinished basement with insulation in the floor joists or in an attic where the roofline is uninsulated).

5. Duct insulation

The requirements for duct insulation have been revised slightly. The new language makes duct insulation requirements dependent on location and the diameter of the duct.

What’s the difference? The 2012 IECC requires supply ducts in the attic to be R-8 and all other ducts R-6. The 2015 code revises the requirements as follows:

  • Supply and return ducts in the attic must be a minimum of R-8 (where ≥3-inch diameter) and R-6 (where <3-inch diameter).
  • Supply and return ducts everywhere else must be a minimum of R-6 (where ≥3-inch diameter) and R-4.2 (where <3-inch diameter).

Potential impact: Although these revisions allow more flexibility, they also require careful attention by your HVAC contractor to not mix up insulation values. Of course, there is always the exception which allows for ducts (or portions of ducts) located completely inside conditioned space not to be insulated. There is also the option to specify all ducts in the attic to be R-8 and everywhere else to be R-6.

Overall, builders will find the 2015 IECC to be a better code than the 2012 version. Not only does it allow for a new and more flexible compliance path (the ERI Compliance Path, discussed in our previous blog post), but also many of the small changes, not included here, have cleaned up the language to make the code easier to understand and comply with.
To learn more about the 2015 IECC changes, check out these additional resources:

• To purchase a copy of the 2015 IECC, visit the International Code Council website:

• For the Department of Energy’s preliminary determination on the 2015 IECC:

• For a wealth of energy codes information visit:


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Ryan Meres

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