Product Trends: Breathable Barrier
authors Kyle Clapham
Years ago remodelers had only a couple of options to protect the wall sheathing and studs from water intrusion before they installed exterior cladding. Asphalt felt, the same material applied to a roofing deck underneath the shingles, became the most commonly used water-resistive barrier (WRB) because of its thickness and ability to absorb any leakage and gradually dry toward the exterior.
Grade D building paper, another asphalt-saturated product, gained popularity in the western U.S. as an ideal WRB behind stucco siding. The lighter weight of Grade D paper compared to asphalt felt makes the material easier to crease and install on inside corners, but the additional thickness of asphalt felt helps prevent rotting and improves its performance in extreme weather conditions.
Asphalt-saturated WRBs come in smaller rolls, however, which increases the time and difficulty of installation. They also tear more easily and can degrade over time with continual exposure to water. Furthermore, the longer an asphalt-saturated barrier remains uncovered on a building, the quicker UV rays will break down the composition and compromise its water-resistant properties.
The development of plastic WRBs, or housewrap, sought to address the shortcomings of asphalt-saturated products. Made from one of several polyolefin fabrics—usually either polyethylene or polypropylene—housewrap impedes water but also allows vapor to escape toward the exterior if liquid reaches the sheathing. As the technology evolves, the products available have proliferated.
Wind-driven rain and solar-driven moisture can bypass even the best cladding, leaving the WRB as the last line of defense for a wall assembly. Water that enters the wall cavity can cause rot and mold, and lead to structural damage as well as health hazards for the occupants. Housewrap must be permeable enough so any liquid that infiltrates the sheathing can evaporate out to the exterior.
Permeability measures the amount of vapor transmission that a housewrap will permit over time, which minimizes the potential for moisture accumulation. A higher perm number or rating means more vapor will pass through the material, regardless of direction; therefore, a high perm number does not necessarily indicate a housewrap will perform better than ones with a lower perm rating.
Some housewraps incorporate thousands of tiny holes, or perforations, so the vapor-tight product can breathe and achieve an elevated perm rating. Although this approach can help keep moisture from being trapped in the wall, a perforated housewrap sacrifices a great deal of water resistance to attain some level of vapor permeability. The ideal range likely falls between 10 and 20 perms.
Other housewraps, such as DuPont Tyvek HomeWrap, allow vapor to flow between the fibers of the plastic fabric as the material resists water penetration. The manufacturer spins extremely fine high-density polyethylene fibers, fusing them together to form a tough and uniform structure that remains continuous throughout the product and withstands the rigors of the construction process.
“The fiber structure creates microscopic pores that resist bulk water and air penetration, while allowing moisture vapor to pass through,” says Alan Hubbell, global marketing manager for DuPont Tyvek. “The performance of DuPont Tyvek HomeWrap exceeds the International Building Code and International Residential Code requirements as a water-resistive barrier.”
Typar BuildingWrap, engineered to deliver a perm rating of 11.7, offers tear-strength three times greater than its competitors, says John Neely, director of marketing and product management for building and construction at Berry Global, which manufactures plastic packaging and protective solutions. Typar also integrates surfactant-resistant technology to preserve water holdout performance.
“A surfactant is any substance that lowers the surface tension of water, thus allowing it to move more easily through a material,” Neely explains. “Soap is a common form of surfactant, and this is why soapy water cleans better than water alone. Surfactants can also be found in many types of siding, as well as introduced to the wall cavity from power washing.”
CertaWrap Premium Weather Resistant Barrier, a housewrap that provides surfactant resistance as well, presents 50 percent longer UV protection than its competitors, says Brian Kirn, senior marketing manager for CertainTeed Siding. The product has a UV exposure rating of 180 days while the competition supplies 120 days, which can accommodate longer construction timelines.
“Before the weather-resistant barrier is covered, ultraviolet rays can negatively impact the barrier material,” Kirn says. “The UV inhibitors in CertaWrap Premium coatings and fibers were proven to provide superior protection compared to the leading competitor.”
Even the best housewrap, however, will not be effective unless installed properly with the correct system of window flashing and sealing tapes. Any penetrations or openings in the housewrap can create opportunities for water to access the sheathing. Improper installation techniques may even direct moisture into the wall assembly and have serious impact on the performance of the entire system.
“Water leaks rarely occur in the opaque field of a wall; generally, most problems occur around penetrations through the housewrap, such as windows,” explains Gary Parsons, fellow of Dow Building Solutions. “Proper installation of housewrap using a system of flashing tapes or liquid flashing [for] penetrations in the weather-resistive barrier is critical to ensure leak-free performance.”
WeatherMate Plus Housewrap from Dow Building Solutions incorporates two layers of material to provide strength and manage vapor flow through the fabric-like product, Parsons says. The controlled permeability creates an escape toward the outside of the home but also limits the inward solar vapor from claddings, such as manufactured stone and stucco, which absorb water.
Cladding materials that retain water necessitate an enhanced drainage plane that can redistribute liquid away from the sheathing and into the ground. Lakeside and coastal areas typically require some kind of drainage as well because of the high moisture loads on exterior walls. Remodelers often compound this problem by installing siding tightly against housewrap without a gap.
“A rainy season or significant rainfall can happen anywhere and create a significant problem,” says George Caruso, director of operations and innovation at Benjamin Obdyke. “Performance isn’t as much dictated by your geography as the quality of the installation and the housewrap’s ability to provide drainage and drying for the wall assembly.”
The company’s HydroGap Drainable Housewrap has a defined 1-mm space to allow 100 times more bulk water to drain from the wall versus standard housewraps, which do not enable water to flow down their surface, Caruso explains. Without an adequate gap, hydrostatic pressure will likely cause the water to drive inward towards the sheathing through fastener locations, he adds.
The International Building Code and the International Residential Code both include a mandate for drainage in the wall assembly. Oregon has already adopted this provision in the International Residential Code, Caruso says, and other states will likely follow suit. Many manufacturers now sell housewrap with draining capability, such as DuPont DrainWrap and Typar Drainable Wrap.
WeatherSmart Drainable, the latest housewrap offering from Fortifiber, blends a bumpy texture that channels water down at more than 95 percent efficiency, says Chris Yount, president of the company. “We offer detailed installation guides that can be easily downloaded from our website. Our field reps also visit jobsites to review mockups [and] provide feedback on installation methods.”
Kingspan Insulation produces a wide variety of housewraps that can be used in any climate and under any cladding, but its GreenGuard RainDrop 3D Building Wrap presents the best drainage, explains Kevin Cutler, director of sales and marketing. “If you are using a hard siding, such as fiber cement, RainDrop would be preferred. Any water that penetrates the siding [can] drain out.”
Securing housewrap to the sheathing with nails or staples will create punctures in the barrier and undermine its capacity to hold out water. Fasteners also jeopardize the potential of housewrap to serve as a sufficient air barrier, which requires the taping of all seams and overlaps to prevent heating and cooling loss. Many housewraps already claim to provide both a water and air barrier.
“Wraps can be installed and sealed in an improved manner [compared to] felt paper to allow for much less air infiltration, giving the building better overall energy usage,” explains Ian Daniels, director of architectural solutions for Tamlyn. “The installation is more important because you can have a great product, but if the install is done improperly, it will negate the effectiveness.”
Block-It House Wrap from Kimberly-Clark features self-sealing technology around staples, nails and screws to allow for simple and fast installation. “Our warranty is intact whether you use cap nails, cap staples, roofing nails or just plain construction staples,” says Scott Tennison, global materials director for Kimberly-Clark. “Our self-sealing technology is very important with any exterior cladding that requires nails or screws, as each will penetrate the weatherization barrier.”
Because traditional housewraps need staples for adhesion, many products might have difficulty meeting the new International Code Council (2015) regulation for air barriers, which focuses on air leakage, says Connor Campanella, residential building envelope manager at Henry Company. Henry Blueskin VP100 Self-Adhered Water Resistive Air Barrier Membrane adheres directly to the sheathing, eliminating the holes created by staples used to attach traditional housewraps.
“Blueskin VP100 will help home insulation perform at its intended R-value while contributing to reduced energy costs and eliminating uncomfortable air drafts,” Campanella explains. “On top of all that, Blueskin VP100 includes a self-sealing technology, automatically creating a seal around nail penetrations and eliminating additional areas for water and air infiltration.”
Delta-Vent SA, a fully adhered air barrier and WRB from Dörken Systems, also eliminates holes caused by the penetrations of attachment fasteners, mitigating the risk of water and air leakage, says Peter Barrett, product manager. “Fully adhered membranes ensure an even application or layer of the adhesive as well as eliminate the risks associated with mechanically attached membranes, such as the repeated puncturing by fasteners—each representing a potential leak point—and the convective loops created by the pumping action of changing pressures on the wall,” he explains. | QR