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Stucco Walls and the IECC

We are approaching to release of the 2010 International Energy Conservation Code. The only step left is the final hearing scheduled in Charlotte, N.C., later in the fall.

The Association of the Wall and Ceiling Industry has elected not to fight the adoption of the portions of the code setting the more restrictive U-values that require continuous insulation on the exterior envelope of the building. The course of action is to solve the constructability problems that are presented by the new code language. In a recent teleconference of AWCI’s Stucco Energy Code Task Group, the consensus of the group was to move forward with two basic designs for a three-coat portland cement plaster wall system incorporating the continuous insulation concept. In order to prove that these two designs will meet the requirements, a series of laboratory tests needs to be conducted. These tests will determine the constructability of the system (Can the walls be built as designed?), durability (Will the walls stand the test of time?), moisture migration through the wall and potential condensation issues, how the walls behave in wind driven rain, and what the probability is of moisture (either from rain or condensation) developing in the stud cavity and heat flow (Will the system really retard the flow of heat [thermal shorts])?. These tests will be conducted in an environmental testing facility and will require building panels using the materials selected. The panels will be subjected to a series of tests that will confirm or deny the properties needed to comply with the requirements of the 2010 IECC.

Working under the assumption that the tests conducted in the environmental laboratory are successful, we then must proceed with fire testing of the designs. Currently, fire-rated designs do not exist for portland cement plaster assemblies that contain foam insulation under the metal lath. In fact, the only insulation in the legacy fire rated designs currently being used is batt insulation in the wall cavity created by the framing members. Fire-rated designs are not required in all states, but there are enough states and municipalities that require fire-rated exteriors that we need to have them in place.

The fire testing will be more extensive than the environmental tests. Because the U-values for the exterior envelope are established by climate zones, the thickness of the continuous insulation will vary depending on the climate zone were the building is located. This means that we will have to conduct at a minimum four fire tests for each wall design. We are looking for a two-hour design and a four-hour design utilizing the basic wall designs. Because of the variable insulation thickness, we will have to test one at minimum insulation thickness and another at maximum thickness. Since each test can cost upward of $10,000, we will conduct small-scale preliminary tests at a facility that will not cost as much. This will also help us determine if the designs will perform prior to committing to the cost of full scale tests. I have been led to understand that depending on the size of the furnace involved, a small scale test is a very effective way to determine the viability of the design, and it is also an indication of how the design will react when placed in a full-size furnace.

This is another “go–no go” waypoint. If the small-scale tests indicate the potential for positive results downstream, we will then commit to the full-size tests. This will be a laborious process. In order for the assemblies to perform at their highest potential, the portland cement plaster will have to undergo the proper curing before being subjected to the heat of the furnace. We will be looking at seven to 10 days of construction time to ensure a good wall assembly.

Now comes the question of how we are going to pay for all of this testing, and why is it justified considering the current economic conditions. First of all, there are many thousands of jobs on the line, not only mechanics but the companies that employ them as well. Stucco is alive and well in many parts of the country. There are alternatives, but many owners and architects want the durability and look of stucco and will settle for nothing less.

AWCI is currently putting together a budget for the costs we estimate will be required to cover the testing. We have already had indications of support from AWCI member organizations to help in the way of funding, materials and labor for the effort. We are in the process of putting together a schedule of events to guide the work required.

Look for more updates later in the year.

Donald E. Smith, CCS, is AWCI’s director of technical services. Send your questions to [email protected] or call him directly at (703) 538.1611.

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