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Code Corner: The IECC 2009 and ASHRAE 90.1-2007 Effect

By: James R. Baty II | Tilt-Up Concrete Association

I received a technical question the other day from an eastern state asking if it was true that Tilt-Up could no longer be built due to the new energy codes.  It seems the contractor had caught wind of changes to the energy code and assumed that Tilt-Up would be one of the casualties of the new requirement for continuous insulation.  The truth couldn’t be farther from that position.

The real question is, what has changed for the construction industry with the increased adoption of the 2009 IECC and thereby ASHRAE 90.1-2007?  Knowing the details will prepare your company to take advantage of the information in your marketing and selling plans.

The energy required to condition spaces in commercial buildings accounts for more than 33% of the energy budget for a building (see figure 1) when you combine space heating, cooling and ventilation.  Since we are about building envelopes, the answer to our question can be quickly referenced in the 2009 IECC Tables 502.2(1) and Table 502.2(2) for Building Envelope Requirements – Opaque Assemblies.  These tables provide the new prescriptive minimum criteria for building envelope design based on the method of construction.  ASHRAE also updated the reference to climate through eight primary climate zones for the U.S. market (figure 2). These direct you to the proper prescriptive requirement in the tables.

In the energy codes, building systems for above-grade walls are classified as mass, metal building, metal-framed and wood-framed and other. What you will find in the prescriptive tables are reference such as:

  • NR = None required
  • R-16 = A minimum R-value using a traditional insulation system with no specific requirements for connection detailing (i.e. faced fiberglass batts compressed at steel-framing members, or between studs)
  • R-5.7ci = A minimum R-value achieved with a continuous rigid insulation layer.
  • R-13 + R-5.6ci = An assembly with traditional insulation system and an additional required layer of continuous rigid insulation.

These insulation designations are provided to give prescriptive simplicity based on the minimum performance required for each climate.

Assembly U-value Compliance Method:

An alternative code option for prescriptive compliance in the energy codes is maximum assembly U-value.  Based on the calculation methods required by ASHRAE for each building system, an overall assembly U-value can be determined.  Additionally, a building system U-value may be determined by thermal testing and thereby rated as a maximum assembly U-value.  U-value, of course, is the inverse of the R-value so a maximum assembly U-value of 0.1 would be an approximate minimum R-value of 10.  Any construction element that thermally bridges or creates discontinuity in the insulation layer must be considered when determining the effective U-value with this compliance method.

So, in order to understand the impact of the code most clearly, let’s take a look at each building type and determine the changes in insulation required based on the climate zone.  I have combined the tables noted above for quicker reference.

Mass buildings
Mass buildings would be those constructed of Tilt-Up, precast, concrete masonry units or full wythe brick as well as CIP concrete. This building type in Climate Zone 1 does not require any insulation. However, in Climate Zone 2 and higher, all mass buildings must have a continuous layer of insulation.

Climate Zone
1 2 3 4* 5+ 6 7 8
R-value NR R-5.7ci R7.6ci R-9.5ci R-11.4ci R-13.3ci R-15.2ci R-15.2ci
U-value 0.580 0.151 0.123 0.104 0.090 0.080 0.071 0.071
The notes * and + represent the requirement for zones classified as marine (primarily the Pacific Northwest and Northern California based on the predominant presence of high humidity) be considered as Climate Zone 5 for building envelope criteria.

Metal buildings
A metal building is to be understood as a traditional pre-engineered metal frame with a cladding and/or insulation system covering the metal frame. All climate regions require insulation for this building type and in Climate Zone 5 and higher, continuous insulation must be present in addition to the spanning fiberglass batt.

Climate Zone
1 2 3 4* 5+ 6 7 8
R-value R-16 R-16 R-19 R-19 R-13+R-5.6ci R-13+R-5.6ci R-19+R-5.6ci R-19+R-5.6ci
U-value 0.093 0.093 0.084 0.084 0.069 0.069 0.057 0.057

Metal-framed are those built with traditional metal stud framing technology (also known as stick-built) and insulated in the framing cavities. Like metal buildings all climates require insulation for this building type. Beginning with Climate Zone 3, however, continuous insulation must be present in addition to the fiberglass batts between studs.

Climate Zone
1 2 3 4* 5+ 6 7 8
R-value R-13 R-13 R-13+R3.8ci R-13+R-7.5ci R-13+R-7.5ci R-13+R-7.5ci R-13+R-7.5ci R-13+R-7.5ci
U-value 0.124 0.124 0.084 0.064 0.064 0.064 0.064 0.064

Wood-framed are those built with traditional wood stud framing technology (also known as stick-built) and insulated in the framing cavities. There is a tag for and other in this category meant to encompass any non-traditional building systems such as SIP, etc. that are not considered mass. Like metal-framed buildings, this category requires insulation in all climate zones and begins the continuous insulation requirement in Climate Zone 5.

Climate Zone
1 2 3 4* 5+ 6 7 8
R-value R-13 R-13 R-13 R-13 R-13+R-3.8ci R-13+R-7.5ci R-13+R-7.5ci R-13+R-15.6ci
U-value 0.089 0.089 0.089 0.089 0.064 0.051 0.051 0.036

The compliance with the values set out in these tables can be achieved simply using a program available online known as ComCheck. Representatives of ORNL and PNWL created this online program to quickly determine if a building envelope will comply developed this program. Some jurisdictions and/or project specifications will even require a ComCheck to demonstrate compliance. Caution must be exercised when using this software, however, since it only knows what the user inputs. If a user doesn’t know the effective U-value or thermal performance of a particular assembly, the project may pass even though it isn’t truthfully in compliance. In other words, just because a concrete block has a 5-in. core of insulation doesn’t make it an R-value of 17.5. Thermal bridging significantly impacts the effective U-value of the assembly.

Therefore, let me provide an answer for the question posed at the start of this article, “is Tilt-Up no longer a viable method of construction in the newest energy code?” The use of solid concrete Tilt-Up panels for any location beyond Climate Zone I based on the 2009 IECC or below the “warm humid zone” of ASHRAE 90.1-2007 for a project not approved as “semi-conditioned” is not supported. However, the advantages of Tilt-Up concrete system are quickly realized in the high-quality air barrier, the amount of thermal mass and the ease of providing continuous insulation. More simply, far less insulation is required than other building systems.
From this information, it is pretty clear the direction that energy codes are headed. The prescriptive criteria, however, are often the least favorable to your ultimate goals. They provide the minimum (maximum) value that you can get away with but what they can’t account for is the true building performance attained by the sum of the parts being greater than the whole. Therefore, the 2009 IECC defers to ASHRAE 90.1-2007 (and in the future -2010) for the alternate compliance path using energy modeling.

Stay tuned in future editions where I’ll offer thoughts on thermal modeling; or consider attending the TCA Annual Convention this year in Amelia Island, FL (Oct 1-3, 2012) where we will feature a presentation on the proper ways for using the energy budget method of compliance.

2 Responses to “Code Corner: The IECC 2009 and ASHRAE 90.1-2007 Effect”
  1. The most common locations regarding insulating material usually are attics plus outer walls.

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  1. […] new IECC and ASHRAE energy codes? Jim Baty with the Tilt-up Concrete Association (TCA) provides an in-depth review of tilt-up wall panels compared to other building systems for new R-value and U-value requirements in a recent article in […]

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TILT-UP TODAY, a publication of the Tilt-Up Concrete Association, is THE source for Tilt-Up industry news, market intelligence, business strategies, technical solutions, product information, and other resources for professionals in the Tilt-Up industry. A subscription to TILT-UP TODAY is included in a TCA membership. Subscriptions for potential TCA members are also available. If you would like to receive a complimentary subscription to the publication, please contact the TCA.