Air Leakage Criteria

Curtailing air leakage through the building envelope is one way to boost the energy efficiency of a building. In the IECC, air leakage requirements are mandatory, regardless of which compliance path is used. The 2009 edition of the code requires the same building envelope air leakage requirements as previous editions. Essentially, openings and penetrations must be sealed and gasketed consistent with construction material and location specifics. Sealing materials spanning joints between construction materials must be able to accommodate expansion and contraction of those materials. The 2012 IECC has adopted requirements for air leakage in commercial buildings. The code lists the following as compliant assemblies: fully grouted cells; paints and coatings; one coat high quality latex, or two coats commercial grade latex paint; heavy duty polyisocyanurate applied to interior; gypsum wallboard with joints sealed; and exterior insulation and finish systems.

In terms of air leakage, typical masonry construction has integral advantages over frame wall construction. First, masonry construction does not have the same leakage sites as their frame wall counterparts. There are no sills in masonry construction as the wall extends from the footing in a continuous assembly. There is usually a tie-beam or bond beam atop a masonry wall, with trusses or rafters set to the top plate. As a matter of course, quality sealing and caulking are critical at the ceiling edge as well as at access to the attic and around all wall penetrations. According to the National Concrete Masonry Association, air leakage rates compiled for a variety of buildings in various climates, though all constructed after 1980, showed that 84 percent of masonry buildings had whole building air leakage rates of less than 2 cfm/square foot at a pressure differential of 1.57 lb/square foot. By contrast, only 30 percent of frame buildings had whole building air leakage rates less than the above mentioned parameters. While the association states that the data was drawn from different references over several climate zones, making conclusions somewhat difficult to draw, the results do indicate that in terms of existing buildings, masonry buildings tend to have lower air leakage rates than framed buildings.

Cleaning Recommendations

As with any building material proper cleaning and maintenance of masonry go a long way to promoting performance. In-progress cleaning is very important, though often overlooked. All excess mortar must be removed and any exposed masonry must be dry brushed prior to the end of each workday. The wall must also be protected from mud spatter and mortar droppings. In terms of a final cleaning, the correct proprietary cleaning must be used. High pressure cleaning methods should never be utilized, and nozzle pressure should not exceed 500 pounds per square inch. The water flow should be at least four gallons per minute and fan nozzle should be at least 40 degrees. The nozzle should be kept at least 18 inches from the face of the units.

Single Wythe CMU: Quality Results

A durable, cost-effective form of masonry construction, the single wythe wall is a viable solution to many of today's pressing concerns. When well designed, this type of construction offers sound solutions in controlling moisture and air leakage as well as meeting low maintenance requirements with a minimum of effort. Properly designed, CMUs can give architects a proven solution for a smart sustainable modern aesthetic.

 

Oldcastle Architectural is the leading North American manufacturer of concrete masonry, lawn, garden, and paving products and a regional leader in clay brick. The group also produces packaged cement mixes, lightweight aggregates, bagged decorative stone, and lime and concrete rooftiles. Oldcastle Architectural operates across 35 states and 2 Canadian provinces. www.Belgardcommercial.com