Masonry Magazine August 2016 Page. 42
MOISTURE MANAGEMENT
will require less change in the cen�ter of the walls and can be dimen�sioned much larger than sections surrounding the perimeter of the wall, where the compartments would require smaller sections to achieve similar results.
Here is a rule of thumb: mois�ture, air and water always move from high to low. For instance, wet material (high moisture con�Rainsceen veneer terra tent) moves to dry (low moisture cotta used alternatively to content); high vapor moves to clad a column and ceiling of low vapor (from outside to inside
structure.
during the warmer months); and high temperatures move to low temperatures (outside to in�side during the warmer months). With this in mind, it be�comes easier to visualize rainscreens and the principles that make them function well in so many different climate wnes.
Air barriers and flashings are critical in rainscreen design because they are placed against the substrate and are the final defense for keeping things dry. Air barriers, when used in rain�screen systems, will be chosen with different criteria than a cav�itywall, though they serve a similar function. The difference in performance is based on the pressure differentials between the air gap and the outside of the building. Air barriers must be durable, so that deflection or "pumping "does not occur and create negative pressures within the air gap. Flashing of the rainscreen wall, when designs require, would follow standard flashing procedure. The flashing should include a small drip edge -in many cases, smaller than the drip found in most cavity wall construction; flashing membrane, usually dark in color; and termination bars, sealed to the air barrier to me�chanically support the flashing for the life of the building. Many rainscreen systems do not require a mortar collection device or individual weep, as the veneer is typically placedaway from the substrate without mortar, allowing full drainage of the water that enters the airgap.
One of the major differences of a rainscreen system versus a cavity wall system is that the layout of the veneer must be exact to keep the building lines horizontal. Shimming of the Z-girts or hat channel is sometimes required to keep a square, level and plumb fa~de. Having an exact layout from the beginning at all corners ofthe building will provide a big return for the installer. In cavity wall construction, the installation of brick and mortar allows for slight corrections to be made in order to make the proper bond. On the other hand, rainscreens do not typically offer the same compensation levels. Therefore, it is recommended to spend the extra time up front, before in�stallation, using quality instruments to set your points. Once installation begins, repairs or unit replacement can usually be performed in the specific location bysliding and resetting the units. This is vastly different from repairing a wet-mortared brick veneer project, where stocking, sawing, cleaning and de�bris disposal become part of the repair.
>>> CASE STUDY
Drainage and Air Circulation Help Prolong the Life and Look of Austin Apartment Complex
Located in Austin, Texas, a new apartment complex offers luxury one-and two-bedroom apartments. Each of the 13 unique floor plans feature hardwood or stained concrete flooring, granite or quartz countertops, stainless steel appliances, spacious walk in closets, and a private balcony. Amenities include an athletic center, a swimming pool and an outdoor grilling area.
For this particular apartment complex, the developer wanted to eliminate as much concern about Driwall Rainscreen 020-1 , a moisture issues as possible. Mold drainage and ventilation mat and decay can ruin the profitability installed on the exterior walls of a project. With the increase in of construction, can be used
building "tightness" for thermal
behind a variety of exterior
protection, moisture problems
veneers, including stone, are on the rise, causing a greater stucco and fiber cement.
need for hydrostatic pressure release and a ventilation method. A decision was made to incorporate Keene Building Products' Driwall Rainscreen 020-1 to alleviate any future concerns related to moisture behind the variety of exterior veneers, which included stone, stucco and fiber cement.
Driwall Rainscreen 020-1 is a quarter-inch-thick drainage and ventilation mat used behind exterior wall systems. The entangled net drainage and ventilation mat eliminates incidental moisture penetrations and problems in siding applications. With the increase in energy efficiency in the building envelope, there is less potential for thermal leakage. By eliminating a ventilation method, siding applications have seen an increase in moisture issues. It was essential to have a means of drainage and circulation of air to help prolong the life and look of the stone, stucco and fiber cement used on this apartment complex.
The full-wall Driwall Rainscreen 020-1 product rolls over the weather-resistant barrier to separate it from the exterior veneers. The airspace that is provided assures that any moisture that penetrates the siding can drain to the exterior.
Moisture and ventilation are essential to proper construction. This Austin, Texas, apartment complex is allowing the walls to breath and stay dry. IMAS
Rainscreen wall systems have been in our industry for a long time. They have stood the test of time, function as intended, offer particular aesthetics to a project and can be managed by many masons with little or no training. IMAS
Steven Fechino is engineering and construction manager
with Mortar Net Solutions, makers of Tota/Flash and
BlockFlash. For more information, call (800) 664-6638, or
visit www.mortarnet.com.
40 I MASONRY � August 2016 � www.masoncontractors.org The Voice of the Masonry Industry