Illinois Energy Conservation Code Training and Support Program
2012 IECC - Frequently Asked Questions - 2012 IECC
II. BUILDING THERMAL ENVELOPE
(Walls, Windows, Doors and Skylights, Roofing, Floors, and Basement walls, etc.)
Q: If a wood-framed wall of a residential building is being re-insulated, what is the minimum required R-value based on our Climate Zone 5A? This is not for the whole wall assembly; the scope of work simply consists of removing and replacing wall cavity insulation and then applying an interior drywall finish.
A: The work constitutes an “alteration” as outlined in Section R101.4.3, Exception 3, requiring replacement with insulation having a density of at least R-3/inch. Note that many of the exceptions outlined in Section R101.4.3 are derivations, in whole or in part, from language appearing in ASHRAE Standard 90.1-2010. In particular, note Section 5.1.3(c) of the Standard. [2012 IECC R101.4.3, 90.1-2010 5.1.3(c)]
Q: Where did provisions for moisture control go? Our community requires the use of a vapor retarder in framed-walls. Acceptable retarders include polyethylene, foil-backed drywall or kraft-paper. Please clarify the moisture control requirements of the 2012 IECC?
A: Neither the 2009 nor the 2012 IECC editions contain provisions for moisture control. Final action to Code Change EC28-06/07 (AM) resulted in identifying and defining vapor retarder materials by Class. Consequently, both the 2009 and 2012 editions of the International Residential Code® (IRC®) now recognize that wall assemblies can be designed and constructed to dry inwards and outwards under particular conditions. The moisture control provisions have been relocated to Section R1405.3 of the 2012 International Building Code® (IBC®) for commercial buildings and Section R601.3 of the IRC for residential buildings. Based on these revised and improved provisions, it is not likely homes constructed in Illinois will require kraft-paper, foil-facings, or even polyethylene vapor retarders any more. Please consult the provisions of IRC R601.3 directly for additional detail.
Where kraft-paper and foil-facing (Class I) vapor retarders, or polyethylene (Class II) vapor retarders are proposed in lieu of latex or enamel paint (Class III), the installation of these vapor retarders shall be continuous over the wall field. Therefore, in order to maintain continuity of the vapor retarder, it would mean the kraft-facings would need to be face-stapled to meet the requirements of R601.3. In addition to restricting water vapor diffusion, the installation of a vapor retarder impedes airflow, provided that it is continuous. Where openings are left in the vapor retarder during installation, either intentionally or by accident, they nullify the control of airflow, and therefore, the flow of moisture.
To summarize, there exist three distinct provisions addressing moisture control and weather resistance for exterior walls in the IECC/IRC, accompanied by a distinct performance requirement:
- A water-resistive barrier shall be installed in accordance with IRC Section R703.2 and Table R703.4, and the manufacturer’s installation instructions (IRC R106.1.2); and
- A Class I, Class II, or Class III vapor retarder shall be installed in accordance with IRC Section R601.3 and Table 601.3.1, and the manufacturer’s installation instructions (IRC R106.1.2); and
- The building thermal envelope shall be durably sealed to limit infiltration by;
a. Installing the components of the building thermal envelope in accordance with IECC Section R402.4.1.1, the manufacturer’s installation instructions (IECC R303.2), and Table R402.4.1.1 by visual inspection; AND
b. Building diagnostic testing and verification as having an air leakage rate not exceeding 5 air changes per hour (ACH) at a pressure of 0.2 inches w.g. (50 Pascal), 5ACH50.
Q: Could you please clarify the intent of the code regarding the reduction of R-5 continuous insulating sheathing referenced in Table R402.1.1, Footnote ‘h’?
A: Since you ask for feedback relative to the intent of Footnote ‘h’, it was very clearly intended that a wall with full structural sheathing still requires the full R-5 continuous insulating sheathing, not R-2, as in the R-13+5ci requirement for Climate Zones 4 and 5.
The original intent was to make it easy to comply with what was becoming a popular approach to wall construction at the time (and still is)—using structural sheathing only at the corners and R-2 insulating sheathing everywhere else—to maintain a consistent total sheathing thickness and a uniform nailing/attachment surface. The 2012 IECC resolves the interpretive inconsistency of the 2009 IECC by clearly limiting the R-value reduction from R-5 to R-2 ONLY to the sheathed portions of walls where the structure is provided with less than 40 percent structural sheathing. Where the structure is provided with 40 percent or more structural sheathing (up to 100%), R-5 continuous insulating sheathing must applied over the entire building thermal envelope
Q: A metal building roof is proposed using batten insulation lapping over purlins and girts. The insulation is compressed at all girts and purlins so R-values will be significantly less at these locations. Are the values specified for “Metal Building Roofs” intended to be maximums, minimums or averages?
A: Often referred to in the industry as “trough-fastened” or “screw-down” metal roofing, a complying prescriptive option no longer exists in the 2012 IECC where the batten insulation is simply draped over purlins and then compressed as the metal purlins (spanning members) are attached. The 2012 IECC now addresses this matter by requiring all metal building roof systems to be provided with thermal blocks to limit conduction and a Liner System (LS) to limit air leakage.
Simply put, a metal building roof complies with the 2009 IECC where the battens are installed along with R-5 thermal blocks as described in Table C402.2. No area-weighted averaging, effective averaging, or averaging of any kind is permitted.
While somewhat dated, the NAIMA Compliance Guide for Metal Buildings (MB304) provides additional detail for typical metal building construction assemblies, and may be found at the following URL: http://www.naima.org/pages/products/mb.html. [2012 IECC Table C402.2]
Q: When using tapered insulation where the insulation is close to zero thickness near a roof drain, is the required R-value [R-20ci from Table 502.2(1), Climate Zones 2-6, “Insulation entirely above deck”] taken as the average thickness over the entire roof or is the minimum R-value required at the roof drain together with the additional tapered thickness on top of that?
A: Neither. The minimum R-20ci [Table 502.2(1), Climate Zones 2-6, and “Insulation entirely above deck”] applies to the area-weighted average U-factor (U-0.048 from Table 502.1.2) of the tapered insulation assembly. However, at no point (i.e., at roof drains) is the thickness of insulation to vary more than 1-inch (25 mm) from the required minimum R-20ci. For instance, if the density of the insulation were R-5/in., and the code-required minimum R-value were R-20ci, then the minimum thickness of insulation permissible at roof drains (i.e., where the taper starts) would be 3-inches (i.e., 4-in. x R-5/in. = R-20; 3-in. x R-5/in. = R-15).
Put another way, Exception 1 to Section C402.2.1 is such that a deficit of no more than 1-inch of insulation is allowed at any point within the roof field (i.e., provided the field is thickened elsewhere to compensate for areas where insulation levels are less than the minimum R-values (thickness in inches) required), such that the overall, area-weighted average insulation U-factor for the entire roof field achieves the minimum U-factor equivalent to the R-value specified in Table C402.2. We see the exception allowing a degree of latitude, while requiring a minimum level of insulation over the entire roof field so as to minimize issues of condensation and energy performance for this particular assembly of roofing components.
Note also that Section C402.2.1 applies to installation of insulation for both low-sloped and structurally sloped roofing systems. There are five generic classifications of low slope roof systems addressed by the International Building Code (IBC) and as identified by the National Roofing Contractors’ Association as follows:
- Built-up roof (BUR) membranes
- Metal panel roof systems for low-slope applications
- Polymer-modified bitumen sheet membranes
- Single-ply membranes
- Thermoplastic membranes (e.g., PVC, TPO)
- Thermoset membranes (e.g., EPDM)
- Spray polyurethane foam-based (SPF) roof systems
Questions posed by The Chicago Roofing Contractors Association (CRCA).
Q: How is continuous Air Barrier Construction [2012 IECC, 402.4.1.1] affected by reroofing, roof recover, or roof replacement alterations as defined by the IBC?
A: On issues pertaining to reroofing, roof recover, roof replacement defined by the IBC, the Illinois Energy Conservation Code, and the 2012 IECC, only items altered or affected by alterations, renovations or repairs to an existing building are required to conform to the provisions of the code as they relate to new construction.
Note there are several Exceptions (1-8) itemized in Section C101.4.3 which permit a degree of compliance subject to approval of the code official. With respect to reroofing (Exception 5), the 2012 IECC considers work affecting roofing insulation an alteration to the building. A roofing membrane, however, is considered a roof covering, and as such, is subject to only to the construction requirements of the Building Code of the jurisdiction, likely Chapter 15 of the IBC. Therefore, work considered reroofing or roof recovering is not subject to the provisions of Section C402.4.1, provided the existing insulation level is unaltered (i.e., unmodified).
The provisions of both the 2012 IECC with respect to alterations and repairs affecting the building thermal envelope, and the IBC specific to alterations and repairs affecting building roof coverings are coordinated in this regard.
Put simply, no continuous Air Barrier is required when the extent of work is limited solely to reroofing, roof recover, roof replacement as defined by the IBC, and the Exceptions (1-8) itemized in Section C101.4.3, which permit a degree of compliance subject to approval of the code official.
Q: There are additional measures to be considered when roof R-Values increase from R-20 to R-25 insulation, as is the case in the 2012 IECC. With adding an extra 1” to 1.5” of insulation comes raising all rooftop equipment such as heating/air conditioning units. Even low, door and window sills must be raised; soil stacks that provide vents for drains must also be extended to meet minimum flashing heights for proper roofing applications, etc.
A: The use of ASHRAE Standard 90.1-2010 as an alternative compliance path for commercial buildings is permitted by the 2012 IECC as it applies to reroofing, roof recover, and roof replacement as defined in the IBC. Table 5.5-5 of Standard 90.1 allows commercial roofs in Illinois, with insulation entirely above deck, to be insulated to R-20 in lieu or the 2012 IECC requirement for R-25. Therefore, both paths to compliance (IECC or Standard 90.1) are recognized compliance options.
Q: The CRCA asks whether the State of Illinois, in pursuing the adoption the 2012 IECC, had considered that Illinois jurisdictions typically adopt and apply earlier editions of the ICC International Codes.
A: Yes. The Illinois Energy Code Advisory Council, in making its recommendations to the Capital Development Board (CDB), considered this very issue at length, for Illinois jurisdictions adopting earlier editions of the ICC International Codes. Accordingly, Administrative Rules to adopt the 2012 IECC with amendments were filed with the Secretary of State, May 4th, 2012 in Issue 18 of the Illinois Register. The 2009 IECC will stay in effect until the rules process is finished or until January 1, 2013, the effective date of the 2012 IECC in Illinois.
Q: The CRCA asserts the use of prefixes ‘R’ for designating Residential provisions and ‘C’ for designating Commercial provisions is confusing in the 2012 IECC.
A: The ICC Board of Directors approved of the format change to the International Energy Conservation Code for the purpose of improving clarity in assigning maintenance of code proposals.