IBC Section 1403.2 – Weather Protection

Starting with the basics, the IBC states that “Exterior walls shall provide the building with a weather-resistant exterior wall envelope.” The intent is to protect the wall assembly materials and the building interior from the detrimental effects of the exterior environment. In particular it goes on to require four specific measures to achieve this intent:

Flashing. First is the use of flashing (discussed in detail in 1405.4) that is installed to prevent moisture from entering the wall assembly or to redirect it to the exterior where that happens. The code is rather specific about listing multiple places where flashing is required including door and window perimeters, wall penetrations/rough openings, terminations, and intersections with other elements and projections.

Water-resistive barrier. Second, the IBC requires the prevention of water accumulation in the wall assembly by requiring a water-resistive barrier behind the exterior wall covering. This barrier layer is described in more detail in Section 1404.2 but essentially calls for a minimum one layer of an approved material such as No. 15 asphalt felt complying with ASTM D 226 for Type 1 felt or other approved materials. This barrier can be attached to the exterior side of studs or sheathing but if conventional stucco is used, then the code requires two layers of water barrier. (This barrier will need to be fire tested as part of the testing discussed further for the overall wall as well.)

Drainage. Third, it goes on to require that a means of drainage be provided for any incidental water that does enter behind the exterior wall covering. This can take on the form of properly flashed weepholes detailed into masonry veneer construction or similar appropriate detailing at the bottom of rain screen assemblies where other finish surface options are used.

Condensation prevention. Fourth is protection against condensation forming in the wall assembly (addressed in 1405.3 and the International Energy Conservation Code, IECC). There are somewhat different provisions for different climate zones in the U.S., but code compliance is essentially achieved by providing a Class I or II vapor retarder in the exterior wall. Class I is described as sheet polyethylene film or non-perforated aluminum (foil) creating a very high level of protection. Class II is described as kraft paper faced batt insulation providing a lesser but acceptable level of condensation protection. Not allowed in this case is a Class III vapor retarder which is defined as latex or enamel paint.

International Energy Conservation Code (IECC) – 2012

One of the benefits of the full family of International Codes developed by the International Code Council is that they have been developed together so they are compatible and complementary with each other. This is the case with the IECC which builds upon the basic building code provisions in the IBC and adds compatible requirements for energy efficiency in buildings. As a comprehensive energy conservation code, it establishes minimum regulations for energy-efficient buildings using prescriptive and performance-related provisions. While the IECC addresses both residential and commercial buildings, Chapter 4 focuses specifically on commercial buildings.

With respect to energy-efficient design, the first fundamental decision that needs to be made is which energy code will be used in the design of a commercial building. The IECC recognizes that there are highly developed national standards in place with the similar intent for energy efficiency and therefore has adopted them by reference. The most significant one is the ASHRAE Standard 90.1, the latest edition of which is 2010. Since this standard addresses all of the same items and issues as the IECC, code compliance can be demonstrated using either the criteria listed solely in the IECC or using the criteria in ASHRAE 90.1. There are some differences between the two in that one may be more stringent or lenient than the other on certain specific items. However the end result for determining overall energy efficiency is regarded as equivalent.

There is a catch here, however. The entire design team must agree on which basis is being used to demonstrate compliance with the code on all aspects. Either all of the IECC provisions or all of the 90.1 provisions must be selected—they cannot be co-mingled. The choice will affect all aspects of energy efficiency including the entire building envelope, fenestration, mechanical systems, lighting design, and electrical loads. Since we are limiting our discussion to exterior walls here, the distinction is slight, since items addressed in both the code and 90.1 are the same, although requirements vary slightly. Familiarity with the actual language in the selected compliance path will obviously be important for specific building projects with specific design teams.

In regards to exterior walls, there are essentially two significant requirements that have been updated in the IECC and addressed in 90.1. These two items are added in addition to the four listed in the IBC.