As of January 1, 2011, many states, including Idaho, adopted new energy code requirements with the 2009 International Energy Conservation Code (IECC). The new code has stricter requirements for the energy efficiency of the building envelope (a technical term for the part of a building that keeps the interior warm, dry, and comfortable). The new code requires a roughly 8-10% upgrade in building thermal efficiency from the previous code.
The biggest changes affect insulation values in ceilings, below grade walls, and to a lesser extent, above grade exterior walls. The insulation requirements vary within 8 different climate zones. North Idaho and much of the Intermountain West are in climate zone 6, which has only slightly lower insulation requirements than zones 7 & 8. Zones 7 & 8 encompass the very coldest parts of the country.
Here’s a quick overview of the new requirements:
- Ceiling insulation values have been increased from R-38 to R-49. (The R-value is a measure of thermal efficiency – the higher the number the more efficient the insulation). This is significant and potentially costly to homeowners, especially if they want vaulted ceilings. Typical roof framing members are not deep enough to accommodate enough conventional fiberglass insulation to achieve this high R-value. There are options that can be employed to meet this requirement and still have vaulted ceilings.
- Use deeper rafters. This is potentially expensive, an inefficient use of resources, and generally not recommended unless structural requirements dictate it.
- Use urethane spray foam insulation, which has a much higher R-value per inch. This product is more expensive than fiberglass insulation, but is an excellent air seal and eliminates the need for venting, which is sometimes difficult on complex roofs.
- Use fiberglass insulation in the rafter space, and then a continuous rigid board insulation on either the ceiling below the rafters or on the roof above the sheathing. This reduces thermal bridging, which is a major source of heat loss in stick frame construction. Depending on the application, it may be better to put board insulation on the interior; putting it on the roof is physically easier but makes attaching some types of roofing problematic.
The code does allow for some R-value reductions if certain details are used, and there is an allowance for a maximum of 500 S.F. of vaulted ceilings with R-38 insulation value, subject to some restrictions.
- Basement wall insulation values have been increased from R-13 to R-19. These numbers are for insulation in wall cavities, if continuous board or spray foam insulation is used R- 15 is required. This accounts for the reduction in heat loss through thermal bridging, as mentioned above. One implication of this is that basement living space will potentially be reduced because walls need to be thicker to accommodate more insulation. Use of an ICF foundation system is an effective way to achieve this R-value without losing interior space.
- Exterior wall insulation value has been increased from R-19 to R-20. This is significant because conventional fiberglass batt insulation is not able to achieve R-20 in a 2 x 6 wall. As an alternative, the code allows for a cavity insulation value of R-13 if a continuous board or foam insulation of minimum R-5 is used as a supplement. This is, again, an acknowledgement of the value of reducing thermal bridging. Urethane spray foam insulation can easily achieve R-20 in 2 x 6 stud cavities.
The new IECC has upped the ante for reducing building energy consumption, and future versions of the code promise further improvements. I have always been an advocate for maximizing the thermal performance of any new building, and hyper-insulating is a very effective means of achieving that goal. Money spent up front in insulation will be rewarded through reduced energy costs, smaller mechanical systems, and enhanced comfort levels for building occupants.
Tom Russell, LEED AP, Project Architect
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