2012 IRC INSULATION CODE CHANGES

The 2012 International Residential Code (IRC) insulation requirements have changed. Currently, Teton County is using the 2006 code. While an exact date has not been set, it appears that somewhere within the next 12 months Teton County will be adopting the 2012 IRC. Should you have any clients that are in the conceptual stage of drafting plans, it is possible that by the time those plans are finalized and submitted to the building department that the 2012 code may be in place.

The goal of the 2012 IRC is to make buildings 30% more energy efficient over the 2006 code. The new code outlines several required methods for doing this. While Teton County can modify the code as part of its adoption, it is my understanding that Teton County will modify the 2012 code as listed below.

We have outlined the new major energy components of the code and have given input as to our opinion of the pros and cons of the code -

1: Rigid board insulation sheathing is now required on the exterior of walls. The 2012 code calls for walls to have either an R5 of exterior rigid board and an R20 of cavity fill insulation, or for walls to have an R10 of exterior rigid board with an R11 of cavity fill insulation. Teton County has indicated that they are modifying the code requirements to meet the following: Walls that have the R5 of exterior rigid board will be required to have third-party verification of the interior vapor barrier installation. Walls with an R10 of exterior rigid board will NOT be required to have third-party verification of the vapor barrier. As an alternate, instead of using rigid board on the exterior of the walls, Teton County will allow the use of 1/2" rigid board on the interior walls with the rim-joists spray foamed.

2: Non-vented roof insulation is now required to be composed of a 60% minimum of air-impermeable insulation. (The old code required all of the non-vented ceiling insulation to be air-impermeable).

3: Vented crawlspace floors are required to be R38, or to have sufficient insulation to fill the floor joist cavity.

4: An air barrier is required in the entire building envelope.

5: Plates and framing need to be caulked as part of the air-sealing package.

6: Rim joists need to be sealed as part of the air barrier system.

7: Blower door testing is required.

8: Mechanical air exchange is required.

So in a nutshell, the new code requires increased whole wall insulation values via rigid board with air barrier and air sealing installations, in addition to mechanical ventilation. Here are our thoughts on these changes -

1: Exterior Rigid Board - This provides a thermal break over the framing. The need for this may be marginal on homes that are built with simple framing 24 OC. The type of construction in Teton County seldom allows simple framing. The seismic engineering framing requirements can add a substantial amount of framing area, and adding the rigid board to the exterior provides an effective thermal break.

The problem with installing rigid board on the exterior side of an assembly is that it creates a vapor barrier with a condensation surface dew point on the wrong side of the building assembly. There are many thoughts on this issue.

One thought is to not use a vapor barrier on the interior, with the idea that any moisture that gets into the cavity during the cold weather season would migrate back out of the cavity during the warm weather season. If the warm weather season is long enough and hot enough, this method can work. In cold weather areas, moisture could be inside the wall assembly for most of the year, if not year round, as the drying process is limited. It does not sound like this will be allowed by Teton County.

Another idea is to install a vapor barrier on the interior side of the wall assembly to prevent any moisture from entering the cavity. This creates a double vapor barrier in the wall and any moisture that gets into the cavity would be trapped there, most likely forever.

Teton County's modification of the code regarding third-party inspection of the vapor barrier is due to concerns about condensation if using 1" of rigid board. They feel that this creates a situation where condensation will occur. The third-party verification of the vapor barrier is to help alleviate those concerns. No details have been given as to what the third-party requirements will be, or what the procedure will be for damage done to the plastic during the drywall, misc. cabinets, etc. application. Airtight electrical boxes will probably be required with this application. Teton County feels that if installing 2" of rigid board on the exterior that the condensation concerns are reduced to where no third-party inspection of the vapor barrier is needed.

In the past we have seen, in ceilings, cases of where rigid board has been used for baffles and fiberglass with plastic installed under the rigid board, where there has been condensation issues. In less severe climates, there probably are no problems with this method. We are leery of this type of application, but if you have a perfect and permanent vapor barrier, this combination may work.

Another method is to spray foam the cavity with closed cell foam. This solves the moisture and condensation issue and when combined with caulked framing, this creates the required vapor barrier-air barrier and eliminates the need for airtight boxes.


Installing the 1/2" rigid board on the interior, if using foiled-faced rigid board, provides an effective vapor barrier. While the interior application of the rigid board provides a thermal break where it is installed, interior wall pockets and rim joists will not have a thermal break over them.

2: Non-Vented Roofs - Previous code required all the insulation in an unvented ceiling to be air-impermeable (rigid boards or spray foams). This was to stop condensation in non-vented cavities.

The new code recognizes that if enough air-impermeable insulation is installed, the dew point is pushed far enough into the building so that adding a smaller amount of air-permeable insulation, such as batts or cellulose over the foam, will not reduce the surface temperature of the foam low enough to create a condensation surface. This is slightly less than a 1/3 to 2/3 rule, where 2/3rds of the insulation needs to be foam and 1/3rd can be batts. (Per the 2012 Code, an R49 ceiling requires an R30 of foam to be able to have an R19 batt installed over it. A R60 ceiling would need to have an R36-R40 of foam before adding batts over the foam.)

We feel that this combination will work for condensation control. However, the real world effective R-value of fiberglass insulation is much lower than the labeled R-value due to the testing methods used. This foam-batt hybrid system is only slightly cheaper than using all foam products, and the hybrid foam-batt performance is less than using all foam.

3: Air Barriers - Air barriers are comprised of several different products or a combination of products. The goal is to prevent air from passing into or out of the building. We feel that while this is important, stopping any air movement within the insulation is equally important, as any air movement via convective looping will greatly reduce the effective R-value of any fibrous insulation. One of the most important elements of an air barrier is selecting one that will not be compromised with penetrations either during or after construction, and one that will last the lifetime of the building.

Exterior Air Barriers: These products can be an approved house wrap material or a liquid applied material. Liquid applied materials are generally used on masonry walls. House wraps are an inexpensive air barrier. The manufacturers instructions for caulking and taping and fastener type must be adhered to. Penetrations caused by the siding application can cause the air barrier to leak.

Interior Air Barriers: This can be any material that stops air from leaking through the cavity into the building. Drywall is an air barrier when it is caulked to plates and window framing. Plastic can be an air barrier. Both of these products require airtight electrical boxes so that the boxes can be sealed to the drywall or plastic. Plastic will be compromised by drywall screws and is subject to tears during the drywall application. During the lifetime of the building it is likely that penetrations will be made into the drywall or plastic, compromising the air barrier. Spray foam is an especially effective air barrier as it is not subjected to penetrations and does not require airtight electrical boxes.

Ceiling Air Barriers: If the ceilings are finished with drywall or if they use spray foam, the caulked and sealed drywall or the spray foam can serve as the air barrier. Other ceiling finishes would require spray foam or some other type of air barrier to be used. Dropped tile ceilings will present a challenge for an air barrier when using conventional fibrous insulation materials.

4: Air Sealing - The code calls for the plates, framing and rim joists to be sealed. When spray foaming the cavities, caulking the framing truly seals up the house. While caulking may be required if using fiberglass or cellulose, these insulation products are not air barrier products and allow for air infiltration. We feel that caulking these fibrous insulation assemblies, while maybe required by code, is of little value.

5: Mechanical Ventilation - This is required under the new code and is needed to provide fresh air for tightly sealed buildings. Mechanical ventilation costs have come down immensely over the past 10 years. Of all the appliances that can be installed into a home, having a good mechanical air exchange is the most important.

6: Blower Door Testing - This is typically done after the drywall is installed with the reasoning that drywall makes a good air barrier. It should not be assumed that the drywall would be the air barrier unless the drywall is caulked and sealed as required to perform as one.

We do not have the exact details of what the soon-to-be-adopted code will entail, but we believe that it will contain the above basic requirements, which will change how buildings are insulated.

It will be important to specify on the plans which product/system i.e.: drywall, spray foam or house wrap - will be the air barrier system, so that the appropriate trade is aware of their scope of work in the proper installation of the sealed air-barrier system. If puncture prone products, such as plastic are used for the air barrier, inspection during the drywall installation is important to ensure that nothing is torn, as this is critical to passing the blower door test.


As always, please let us know if you have any questions.


David Bressler