By Jim O’Neill
Masonry structures are known for having high durability, which is why they are built to last for 100 years. Current building codes emphasize energy efficiency, which has made influential changes to masonry veneer wall systems. The two most influential changes are the additions of continuous insulation and air barriers into the masonry cavity. These additions greatly enhance energy efficiency. However, the addition of continuous insulation causes masonry cavities to lose air space, frequently as much as 50%. This is the new era of brick veneer, the era of smaller air spaces in veneer walls. Improper ventilation systems based on old technology can cause excess moisture, affecting the durability and longevity of the structure. Therefore, properly detailing these walls is crucial.
There are two keys to drying in veneer cavities: drainage and ventilation. Drainage requires an opening or weeps at the bottom of the wall to allow any incidental moisture to escape the veneer system. Ventilation requires an opening in the cavity large enough to allow air to enter, flow through the cavity, and then exit. Unfortunately, mortar bridges can block the ventilation and prevent the drainage system from working properly.
|25 mph||50 mph|
|Wall 1 (Product A)||15.8 cfm||24.2 cfm|
|Wall 2 (CAV-AIR-ATOR)||37.9 cfm||51.4 cfm|
Table 1 — Air Infiltration Test Results
|Amount of water||Drainage time||Collected|
|Wall 1 (Product A)||5 gallons||10 minutes||4.62 gallons|
|Wall 2 (CAV-AIR-ATOR)||5 gallons||10 minutes||4.70 gallons|
Table 2 — Water Drainage Performance Test Results
Mortar bridging in brick veneer walls occurs when ventilation spaces are too thin to stop mortar from clinging to the interior wall. These mortar bridges create a space for water to collect, which impedes ventilation and drainage. In this scenario, traditional mortar collection devices are useless, because the mortar dam is formed above the bottom of the wall. The solution is to use full wall drainage systems.
Keene Building Products, along with Architectural Testing Inc., performed a test of several 1-inch brick veneer walls with 1 inch of air space to compare the performance of drainage and ventilation products in a cavity wall. Wall 1 consisted of Product A, a dovetail mortar collection device that utilized three weep vents in the top and bottom courses of the brick. Wall 2 included Keene’s CAV-AIR-ATOR™ full drainage system and three Driwall™ weep vents in the top and bottom courses of the brick. Each wall was constructed with a single course of bricks with a 1-inch cavity. Walls were constructed according to standard building practices using the same materials; all products were installed to manufacturers’ recommendations.
Air Infiltration: ASTM E 284-04, Standard Test Method for Determining the Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen. Testing was conducted at 1.57 psf (25 mph) and 6.24 (50 mph) positive static air pressure difference.
Water Drainage Performance Test: This test introduced five gallons of water into each cavity wall and captured the amount of water drained out of the weep vents.
It can be seen how changing from a simple mortar collection device to a full wall system can increase the drying potential of the wall. In these tests, Wall 2, the full wall system, increased ventilation by 75% when compared to traditional mortar collection devices. Furthermore, unlike traditional products, full wall products like the CAV-AIR-ATOR do not require thick cavities in order to perform.
As we build our buildings to be more energy efficient, we reduce the air space behind the brick veneer. Unfortunately, the need for proper drying does not decrease as we move toward energy efficiency. Therefore, ensuring that we maintain an unimpeded air space is critical. Keene Building Products endorses the use of a full wall ventilation and drainage product in brick masonry applications with less than 2 inches of open air space. By installing this type of product in a brick veneer wall, you are eliminating all mortar bridging and dramatically increasing ventilation, while maintaining the energy efficiency of the structure.
Jim O’Neill is Building Envelope Division Manager for Keene Building Products.