It is easy to see that the primary intent of the older Model Code and the new International (I-) Code is identical: the builder’s use of flashings at exterior wall transitions to ensure construction of a fully weather-resistant building envelope.

However, there is a radical difference between these two code sections. Architects should compare the requirements of the following building code sections closely:

  • “Weather-exposed surfaces shall have a weather-resistive barrier to protect the interior wall covering … Exterior openings exposed to the weather shall be flashed in such a manner as to make them weatherproof,” 1997 Uniform Building Code, section 1402.
  • “Exterior walls shall provide the building with a weather-resistant exterior wall envelope … The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior veneer ...” 2003 International Building Code (IBC), section 1403, and 2003 International Residential Code (IRC), section R703.

The difference is the addition to the new I-Codes of two critical words: “be designed.” In those jurisdictions that have adopted the I-Codes, building designers are now responsible for providing to the builder sufficient details and guidance for weatherproof construction of the wall and roof covering systems.

Until the I-Codes’ adoption, architects often were allowed to pass all or part of this design responsibility to the builders by doing nothing more than calling out “building paper” and “flashing” on a typical wall section. We have seen construction drawings in which the architect’s guidance consists solely of the specification: “comply with code requirements.”

If these exterior walls or roofs begin leaking, who do the architects loudly blame? The builders, of course, for their failure to comply with the architects’ overall design intent, represented by their references to building paper and flashing and the code.

It is our experience that this design intent defense by a project architect has worked well in litigation process because the builder’s continuation of the construction constitutes acceptance of the additional responsibility and a commitment by the builder to carry out the work in conformance with the controlling building code.

Later, when building envelope failures result in water infiltration and mold damage claims, the builder’s only defense often is the hollow mantra, “I built it exactly how the architect detailed it.” While literally true, this argument often fares poorly against the design intent defense—unless the designer also has provided regular monitoring of the ongoing work under a contract administration agreement or, as is required in some jurisdictions, has a statutory obligation to oversee the design, and thus should have noticed the defects that resulted in water damage.

Now, with the advent of the I-Codes, building designers have been burdened with the clear responsibility of providing to the builder a weatherproof design for the exterior walls and the roof. “Be designed” is an example of a performance requirement. Designers simply are advised that their design must provide weatherproof performance. The IBC provides little or no prescriptive guidance for achieving this goal, but does require the designer to “provide details of the exterior wall envelope as required.”

An excellent example of the difference between performance and prescriptive language is a comparison of how the IBC and IRC address joint overlaps of loose-laid sheet goods used as the weather resistive barrier. The IRC (Section 703.2) prescribes minimum 6-inch vertical overlaps and minimum 2-inch horizontal overlaps, while the IBC (Section 1404.2) simply requires the overlaps to be appropriately configured to provide continuous water-resistive performance.

Under the IBC, as the building designer specifies the weather-resistive barrier, he is expected to evaluate local climate conditions, the potential effects of the building’s exposure and the expected performance of the cladding and flashing systems to determine appropriate overlap dimensions. Unfortunately, some designers will remain unaware of the new design and performance requirements of the I-Codes until the issue is raised by a construction attorney representing the owner or builder of a damaged building.

August 2007
Issue Eight, Volume Two

This article by Colin Murphy and Lonnie Haughton.

Colin Murphy
Murphy is a founder and managing partner of Trinity | ERD.

Lonnie Haughton
Haughton is a construction codes and standards consultant with Richard Avelar & Associates.

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