Product Trends: Moisture Management

Rainscreens have become increasingly popular in the remodeling industry, providing a range of benefits from moisture control to sustainable design.

by Emily Blackburn

Rainscreen systems are nothing new; they’ve been utilized in commercial builds for decades. However, it is only recently they’ve taken off in the residential market—and for good reason. Changing climate patterns leading to more intense rainy seasons, as well as advancements in building wrap technology, have led to an increased need for and awareness of rainscreen systems.

What Is a Rainscreen?

When talking about rainscreens, it’s important to be clear on what exactly they are. “A rainscreen is actually a building design,” explains Keith Lolley, president of Advanced Building Products, which produces the Mortairvent Rainscreen. “It’s not an actual product. That’s one of the things we try to educate the industry in. A lot of people refer to them as rainscreen mats—they’re really drainage and ventilation mats that are used for a rainscreen function,” he says.

Mortairvent Rainscreen has a 93-95 percent open design and allows for efficient airflow and ventilation, helping to circulate air and dry the interior wall components. |

A rainscreen system is an exterior cladding infrastructure that protects the building’s weather-resistant barrier. It consists of an outer layer that is separated from the building’s structural wall by an air gap. This gap allows air to circulate, which helps to prevent moisture from penetrating the building’s envelope.

Envelope types vary: Weather resistant barriers (WRB) are a type of building envelope material that is designed to prevent air and moisture infiltration while a drainable housewrap is a type of WRB that is designed to allow moisture to escape from the wall system. Both are important components of the building envelope and work together to prevent moisture damage.

“The difference between a rainscreen and a drainable house wrap is the whole drainage and ventilation aspect,” Lolley says. “A drainable housewrap has about a 1-millimeter space to it, and it drains 90 percent usually. It’s a very good housewrap, but it’s not a rainscreen because to be a rainscreen, you need to have positive and true ventilation, and you need to have around 3 to 4.5 millimeters of space.”

Rainscreens provide a two-line defense against water intrusion, protecting the structure from water damage, mold growth and other moisture-related issues.

Tamlyn’s TamlynWrap Rainscreen 6.3 is a 3-in-1 Water Resistive Barrier system that enhances drainage and drying proficiency. The 6.3-millimeter filament is uncompressible and reduces installation cost by acting as a furring strip.

The most traditional rainscreen system involves furring (or batten) strips, which create a gap between the cladding and the weather-resistant barrier, allowing for proper ventilation and drainage.

Kaylen Handly, market development manager for Benjamin Obdyke, explains that wood furring strips are the “original” method of creating a rainscreen system and are still considered a “go-to” option. “In most cases the furring strip would be about a 0.75-inch space just because that’s what traditional ‘one by’ material comes to— about 0.75 inches. So, they would do a vertical strapping to create this rainscreen space, which is a great way to build because now that furring strip can be structural, so as you’re building it out, you can attach your cladding directly to that furring.”

“The problem with [wood furring strips] is not every board is the same dimension,” Lolley explains. “So, on a jobsite, you have to shim, you have to cut, you have to manipulate to make sure it works. That’s why these new engineered furring strips are great because every single one is the exact same size and dimension, and some have dual drainage and ventilation side ventilation, whereas others just have a lot of surface-to-surface contact.”

However, Handly adds that while furring strips are effective, newer technologies are even more so. Benjamin Obdyke’s Slicker line is able to create more drying potential with only a quarter of an inch because it’s 90 percent open. “So, instead of having wood furring strips that are compartmentalized and obviously can’t dry through the wood, it’s only going to be vertical. With our Slicker product, you have a convective drying that can go laterally—around windows or around doors—to create more drying potential with a smaller space.”

Benjamin Obdyke’s Slicker product line is a vertically channeled, three-dimensional drainage and ventilation system that provides a continuous space for drainage and drying, a thermal break, and pressure equalization.

An alternative to furring strips is the aforementioned drainage mats, also known as entangled nets. Entangled net rainscreen systems are a type of rainscreen system that uses a drainage mat made of a heat-bonded filter fabric to eliminate incidental moisture problems in most exterior veneer applications including stucco, manufactured stone, and plank siding. “What that does is it allows the scratch coat from your mortar applications to be blocked by the fabric, but it allows the moisture to drain through the fabric and have a clear unobstructed path down the wall out the building,” Lolley explains.

Entangled nets offer a number of benefits, from their lack of stretch preventing the wall application from being wavy to allowing for a fabric flap that can prevent bugs within the capillary breaks from entering the home.

Mortairvent, Advanced Building Product’s residential rainscreen system, utilizes a channel design with rows of entangled mat that creates a continuous 6 millimeter space for drainage and ventilation, allowing excess moisture to drain from the wall system and ventilated air to circulate and dry the interior wall components.

Ever-Expanding Options

Michael Anschel, owner of Otogawa-Anschel Design+Build in the greater Minneapolis area and CEO of Certified Green, Inc., has been educating remodelers on the advantages of rainscreen technology for almost two decades. “I want to say early 2000s is probably when we started using them,” he says. “And there weren’t a lot of good products on the market to get it done.”

He recalls an educational video that he and Carl Seville, owner of Seville Consulting, made almost a decade ago and dubbed “The Green Police.” “[We were] talking about how, if we could just get people to start using ventilated rainscreens, you know, what a difference it would make for the building industry.”

Anschel notes that he is very deliberate in the addition of the word ventilated because, “Ventilated rainscreens dramatically outperform [traditional] rainscreens. When you think rainscreen, think ‘seatbelt.’ When you think ventilated rainscreen, think ‘airbag and seatbelt.’ Now, instead of a gap of 3 or 4 millimeters, we have a gap of three eighths of an inch (9.525 millimeters). Now, we have accelerated draining.”

Keene Driwall Rainscreen is an entangled net product for exterior wall systems that eliminates incidental moisture problems in most exterior veneer applications.|

In addition to the wider capillary space, ventilated rainscreen systems have gaps at the top and the bottom. The difference in pressure between the group and 20-to-30 feet in the air might not seem significant, but it’s enough to draw air through the gap as the water flows down.

Stressing that there are a lot of ways to incorrectly install a ventilated rainscreen, Anschel says it’s very common to gap and then seal. “What that does is create a chamber at one pressure and atmosphere and another chamber that was another. This creates a drive for the water to go through into the cavity, which we don’t want.”

Long-Term Solutions

It’s not just long, unpredictable rainy seasons and the threat of mold that is driving the increase in interest and application of rainscreen systems. According to Lolley, “Demand for these types of products has grown greatly due to the fact we’re now in the 2021 International Residential Building code.”

The new building code calls for a 5-millimeter airspace with drainage efficiency of 90 percent. “Now, that’s a little misleading because drainage efficiency of 90 percent means that a drainable housewrap meets the new building code,” Lolley explains. “But if you’re doing a stucco or a stone or any kind of a scratch code application where the mortar goes up against that housewrap, you lose the drainage efficiency, and now you fall under 90 percent, so you don’t meet code.” Hence the need for a more comprehensive rainscreen system. Mortairvent’s 6-millimeter gap allows for compression—even if it occurs, it will still be within the 5 millimeter requirement.

“We’ve had catastrophic failures in the Mid-Atlantic area since the early 2000s with stucco and vineyard stone,” Handly says. “And really these assemblies failed because they had the stucco directly on a housewrap. There’s been class action lawsuits since the early 2000s, and eventually the code changes because of these failures.”

The latest recommendations also state that any place in the United States that receives 20 inches or more of rain (or snowmelt) a year needs to design their walls with a capillary break. Excluding arid regions, this covers a majority of the U.S. Municipal codes across the country have begun reflecting these standards for new builds, with remodeling soon to follow.

Benjamin Obdyke Slicker CLASSIC has a narrower ventilated space but operates with the same patented vertical channel design to optimize ventilation. |

Though no insurance policies reflect these changes yet, homeowners who want to get ahead of the curve and protect the longevity of their home at the same time would do well to consider rainscreen systems as part of their next remodel.

Lolley lays it out in plain terms: “The industry average is $5,000 in payout if you have mold rot or any kind of moisture-related issues. So what a lot of us tell people is [rainscreen systems are] a very cheap insurance policy because most manufacturers have at least a 25-year warranty on these products. And if you’re a typical 2,000-square-foot home, you’re looking at between $2,000 or maybe $3,000 in extra costs that’s going to save you possibly $60,000 to $100,000 in restoration down the road.”

Homeowners, and even other remodelers, might question the need for rainscreens—after all, older buildings have survived decades, if not longer, without moisture issues.

This is due to the way older buildings were constructed with large gaps in the sheathing. “In older construction, we did not have all these different control layers,” Handly explains. “So, we had a lot of energy that was lost through the building envelope, which in turn helped to dry it out because we had so much heat or energy moving through. So, if it were to get wet, it could dry. We don’t have that luxury anymore because it’s so airtight.” In addition to moisture control, rainscreens help regulate the temperature and energy efficiency of a house.

“It’s one of those things that it’s only taken us 15 years to be an overnight sensation,” Lolley says. “I always say innovation means new; it doesn’t always mean better. And with that being said, we have a lot of innovative products on the market right now in claddings; and they look beautiful, but some absorb more moisture than ones of the past, which is fine. We just need to design our walls to prepare for that moisture.” QR

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