Masonry Magazine July 2003 Page. 18
Building Codes
Air leakage is usually much more destructive to the integrity of the exterior wall system than vapor transmission.
The success or failure of air barriers boils down to how the details are addressed: where products stop and start, where backup systems change, movement joints, penetrations, utilities, and more. According to the "Construction Waterproofing Handbook" (McGraw-Hill, 1999), "As much as 90 percent of all water intrusion problems occur within one percent of the total building or structure exterior surface area."
So, achieving an effective air barrier system means a lot more than spraying a typical below-grade waterproofing on a block backup wythe. It is particularly important for designers and installers to realize that those problematic points often occur above the ceiling and below the roof deck or floor above. Many case studies have demonstrated that moist air will rise through suspended ceiling tile and then exfiltrate into the exterior building envelope through the many clumsy details such as top of wall, penetrations and joist bearings, to name a few.
Wisconsin official Lauersdorf notes in "Minimum Requirements and Guidelines for the Exterior Building Envelope 2001" that "air leakage is usually much more destructive to the integrity of the exterior wall system than vapor transmission. In fact [it] may be the leading cause of wall problems (in Wisconsin)."
Just what wall problems are coming up? In climates with significant freeze/thaw periods, moisture can get into an exterior wall system, reach its dew point and create frost or condensation. Depending on where this occurs, negative effects may be stud corrosion, tie corrosion, reinforcement corrosion, mold, mildew, degradation of insulation R-value, brick efflorescence and/or spalling, water on interior finishes, and increased energy costs. Designers and constructors need to be particularly aware of projects that may have high interior relative humidity levels, such as hospitals, nursing homes, swimming pools, museums, libraries, food processing, printing centers, etc.
The next question is where to locate an air barrier in the exterior wall. The answer is: it depends, starting with regional guidelines. Wisconsin code puts it on the interior side of the wall insulation. In a brick and block cavity wall design with the rigid insulation in the cavity, the air barrier is often placed between the insulation and the block backup wythe.
Then there's selection of an air barrier system. While many products will meet air leakage requirements, the trickier part is finding a system to address all the problematic points. Air barrier attributes include: bridging capabilities, expected service life (durability), continuous coverage, and being secured (to a substrate).
Another important factor is environmental compatibility, which influences many a designer. Is the product recognized by environmental standard publications? Does the Volatile Organic Compound (VOC) count meet your local requirements? Does it include minimal manufacturing waste, benign over-spray, non-toxic run off? Is it worker-friendly?
BUILDING CODES: PAST AND PRESENT
Today's building codes can be traced back to the Code of Hammurabi, circa 2200-1800 B.C. The Code of Hammurabi provided for the death of a builder if the construction of a dwelling collapsed and caused the death of the owner.
The first building codes in the United States, established in 1625, addressed fire safety and specified materials for roof coverings. In 1630, Boston outlawed chimneys made with wood and thatch roof coverings. In the late 1770s George Washington recommended that height and area limitations be imposed on wood frame buildings in his plans for the District of Columbia. In 1788, the first known formal building code was written in the United States (in German) in Old Salem, now Winston-Salem, N.C.
Larger U.S. cities began establishing building codes in the early 1800s. In 1865, New Orleans was the first city to enact a law requiring inspections of public places. The National Board of Fire Underwriters published its Recommended National Building Code in 1905. In 1915, the world's first model code organization was established to provide a forum for exchange of ideas regarding building safety and construction regulations.
Prior to the International Code Council (ICC), building safety codes were regional. Most codes were produced by three model code organizations. BOCA National Codes were used mostly in Eastern and Great Lakes states; ICBO Uniform Codes in Western and Midwest states; and SBCCI Standard codes in Southern states. As a result, the construction industry often faced the challenge, and cost, of building to different codes in different areas of the country.
Today, the ICC International Codes (I-Codes) combine the strengths of the regional codes without regional limitations. I-Codes respond to the needs of the construction industry and public safety. A single set of codes has strong support from government, code enforcement officials, fire officials, architects, engineers, builders, developers, and building owners and managers. The ICC code development process allows input from all interested individuals and parties. To ensure public safety always comes first, only government officials are eligible to vote on the final code requirements.
For more information, visit the International Code Council at www.iccsafe.org.
Quality Assurance
THE KEY CONSIDERATIONS are to match a product and application method to specific project needs and to require certified installers. "This is a high quality assurance process," says ABAA's Hudson, who believes that if air barriers are designed into masonry wall systems, trained masons should apply them, giving exterior building envelopes a single source of responsibility.
A number of BAC signatory contractors (and some locals) have joined ABAA and many are now listed as licensed ABAA contractors after completing the required training. IMI New England Director Steve Bolognese sits on ABAA's Board of Directors.
In Boston, Local 3 of the International Union of Bricklayers and Allied Craftworkers (BAC) got an early jump, training its own ABAA-certified instructors and serving as an authorized training delivery agent. IMI training centers across the country are in the same process. "The union is ready to train upon need," says BAC Local 3 President Charles Raso.