Healthier Walls through Rainscreen &
The desire to construct more energy-efficient buildings with tighter exterior envelopes has led to problems of a different sort: an increase potential for mold, mildew and rot. Although, a tighter assembly does create more thermal efficiency, it can also trap water, which frequently leads to the deterioration of the building materials.
“A potential mold problem will always exist when material configurations allow more water to penetrate exterior walls than can dissipate or evaporate (more going in than coming out), resulting in an environment conducive to mold growth” says Dan Johnson, Technical Sales Manager at Stuc-O-Flex International, Redmond, Washington.
In particular, wood-framed buildings built to more stringent codes appear increasingly susceptible to mold and mildew problems, unlike older, drafty and un-insulated structures built decades ago. The lack of deterioration in older buildings does not come from an inherently better resistance to water intrusion, but rather a better ability to dissipate moisture. Forensic evaluations show that building materials deteriorate more rapidly if water is unable to evaporate or drain. Absent perfect design, execution, materials performance and continued maintenance, it is almost inevitable that problems can develop in buildings constructed to today’s code requirements, Johnson says.
Conditions that can lead to potential mold growth include: the presence of mold spores, which are nearly ubiquitous in wet or humid climates; temperatures above 40 degrees F; nutrients of some type including organic material such as wood or paper; the presence of oxygen and moisture levels above 20% - 40%.
Depending on project location and climate, the moisture content of even protected building products may fluctuate at levels just below the minimum required for fungal growth. And if one considers that four of the five elements supporting mold development are inherently present at all times, the presence of even a small amount of additional water can lead to decay and deterioration.
Since modern construction techniques reduce water vapor diffusion and thus increase the time moisture stays in exterior walls, builders and architects should incorporate a defensive strategy to mitigate the effects of water intrusion and prevent rot, Johnson says.
One defensive strategy is to provide a rainscreen configuration or multiple element protection. Unlike face-sealed systems, rainscreen assemblies incorporate a drainage cavity between the building and cladding products with joint and transition details that expel water to the exterior. Separating exterior materials from weather-resistant barriers has had a favorable history in many cladding assemblies, masonry and some metal panel systems. Many below-grade waterproofing designs also incorporate a drainage cavity. These configurations typically use hydrostatic pressure relief through a drainage medium with fascia allowing only water to pass through into an unobstructed cavity.
Above-grade applications also require a design for adequate air movement and ventilation. Unlike below-grade systems, however, above-grade applications do not require design modifications for gallons of water per linear foot, but rather for small amounts of moisture that occur repeatedly. When minor amounts of water are introduced frequently, evaporation is equally if not more important than drainage, Johnson says. Typically, the wider the cavity, the greater the air flow, so that cavities less than 0.25 “ (10 mm) do not generally have adequate convention to remain dry, although water may still fall to the bottom.
Creating Space Through Vertical Wall Drainage Mats
Vertical wall rainscreen drainage mats provide that necessary additional space for drainage. They also contribute to air circulation and ventilation when properly designed. The combination of water drainage and increased air flow will enhance drying and in turn reduce the damaging effects of water penetration.
Building papers and house-wraps are well established in providing some protection against substrate damage. While traditional barriers offer a marginal safeguard, they do not always provide an adequate path for drainage. When siding materials are tightly installed against weather-resistant barriers, opportunities for drainage and ventilation can be inadequate or even blocked. Engineers and designers are now exploring various configurations to remove water from exterior walls while incorporating some mechanism of ventilation.
“Enhancing air flow and managing entrapped moisture makes sense. The challenges lies in a simple, efficient and cost-effective approach,” Johnson says.
From Boston to Seattle, exterior wall drainage mats are gaining currency with some of the most recognized and distinguished building enclosure specialists in North America. In both new construction and cases of cladding remediation, drainage mats are gaining acceptability as a water deterioration solution. “Enhancing traditional claddings with a drainage component configuration assures extended service life, superior product performance, increased customer satisfaction and reduced potential exposure,” Johnson says.
Stuc-O-Flex International offers WaterWay Drainage Mats, which consist of a polymer (plastic) core of fused, entangled filaments in varying thicknesses from a nominal quarter to three-quarters of an inch, depending on desired cavity space and cladding selection. Certain profiles are available with a protective filter fabric bonded to one side, others with 60-minute grade “D” building paper. Even a non-woven, non-perforated polyolefin-based house-wrap is available with drainage mats attached. WaterWay drainage mats are equally effective in designs for traditional stucco, EIFS, manufactured stone, fiber-cement, brick, standard-loop and cedar sidings and other wall system materials.
This technique achieves desired results with limited expense, Johnson says. Rainscreen Drainage Mats run as little as 40 cents a square foot.
Johnson notes that Rainscreen configurations vary. Some are complex and require extensive levels of detail. But the concept remains the same: if you incorporate adequate space and compliment that space with increased air flow, you will reduce the likelihood of decay and extend the service life of your project.
For more information on the WaterWay Rainscreen Drainage Mats line of products, contact Stuc-O-Flex International Incorporated at (800) 305-1046,