Today, there are a multitude of options when it comes to selecting a weather-resistant barrier (WRB). When evaluating a building wrap, builders and specifiers look for a product that has the optimal balance of properties—bulk air and water resistance, durability, and sufficient moisture vapor permeability. A balance of these four properties is crucial in helping to maintain the protection, comfort, and efficiency of a building or home, and the WRB is ultimately the last line of defense for protecting the building from the elements. 

However, there is a fifth property—surfactant resistance—that is commonly overlooked or simply underestimated by building professionals. Without a basic understanding of surfactants and how they impact the performance of building wrap, builders and contractors could potentially jeopardize the long-term durability of the exterior wall assembly. The material must be able to maintain its integrity—no matter what it comes into contact with. This article will: 1) define what a surfactant is, 2) provide an understanding of the surfactant-induced issues, and 3) outline solutions to provide surfactant resistance and, ultimately, peace of mind to builders and building owners.

What is a Surfactant? 

Surfactants (surface active agents) are contaminants that lower the surface tension of a liquid, allowing it to penetrate deeper into the building wrap material. They can be found in a multitude of commonly used construction materials and are one potential threat to a building wrap’s long-term performance. Water-soluble extractives in wood, such as tannins and wood sugars in redwood and cedar, are examples of surfactants that contaminate the surface of building wraps. They can also be found in the bonding agents used in stucco. 

In addition, surfactants can be found in detergents, soaps, and other cleaning solutions used to pressure wash siding, making surfactants nearly impossible to avoid altogether. Water that manages to get into a building system carries these surfactants and allows them to penetrate deeper into the walls, and with that, brings greater opportunities for molding, rotting, and potentially decreased comfort on the inside of the home or building. 

What is the Problem with Surfactants? 

Surfactants promote the loss of water repellency, causing “wetting” of the building wrap surface. Once this occurs, water can more easily pass through the microscopic openings in the building wrap. Once moisture finds its way into the building envelope, it can threaten a building’s structural integrity, causing exterior surfaces to deteriorate. Bulk moisture intrusion can also support mold and rot that not only cause structural damage but also pose serious health hazards to building occupants.  

Ways to Combat Surfactants

It’s important to note that some building wraps perform better against surfactants than others. So, first and foremost, be sure to pay attention to a WRB’s surfactant resistance capabilities. Not all wraps will provide the same surfactant protection—if any at all. On the other end of the spectrum are building wraps that are engineered with a specialized coating that resists surfactants. Often, nonwoven building wraps offer these types of coatings, but it’s important to double-check when specifying.

Beyond product selection, there are several installation best practices that contractors and builders can adhere to in an effort to decrease the potential of surfactant-related issues. Renowned building scientist, Joseph Lstiburek, suggests several steps to prevent surfactants from reaching the building wrap material. When installing wood cladding, Lstiburek recommends back-priming with a water-repellent primer, and adding an air space. Back-priming wood clapboards and trim helps to isolate the surfactants in the wood from the building wrap. Similarly, providing an air space between wood trim and clapboards, using furring or some other spacer, reduces the quantity and time liquid phase water is trapped in the exterior, thereby reducing the potential of surfactant movement. 

Stucco should never be installed in direct contact with building wraps as it can adhere to the wrap’s surface, thereby altering its surface energy and allowing building wrap pores to become "wetted." 

Third-Party Testing Provides Insight

Wetting, weathering, and scratch tests have been conducted to test surfactant resistance, and the results can be consulted to compare performance among different WRBs in the industry. There is long-standing, third-party testing that was commissioned by The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) that showed TYPAR^® wraps resisted a power washing solution, while the leading competitor’s product failed, permitting numerous droplets to form and wet the underlying OSB (2004). 

More recently, a study was commissioned by TYPAR to further explore surfactant resistance across leading WRBs. Conducted in June 2023 by an accredited third-party testing facility with ISO 17025, Miami-Dade, AAMA, and AABA certifications, the testing compared TYPAR^® BuildingWrap^™ to two leading WRBs when subjected to a common surfactant (dish soap and water). Two different tests were completed:

Test #1: UV & Weather Exposure

The first test subjected the surfactant-treated weather barriers to a weathering machine at a temperature of 75ºF for 48 hours, exposing them to heat and UV light. After 48 hours, both the competitive samples were brittle, although one only showed damage after a scratch test was conducted. The TYPAR wrap did not show any damage before or after the scratch test. 

After being exposed to surfactants and subjected to a weathering machine for two days, The TYPAR WRB (left) did not show any damage before or after a scratch test, while the two top competitors (middle and right) both became brittle.

Test #2: Moisture Exposure

For the second test, all three weather-resistant barriers were installed on a mock-up wall with leak detection paper installed behind them. The surfactant was sprayed onto the samples and allowed to sit for 10 minutes. After 10 minutes, each WRB was cut to expose the leak detection paper. 

• The paper behind competitor #1 had slight indications of changing from white to pink, indicating moisture.
• The paper behind competitor #2 had several pink areas, indicating moisture intrusion. 
• The paper behind TYPAR wrap was dry, showing no evidence of moisture. 

Leak detection paper was placed between the building wrap and a sheet of plywood, then sprayed with a soap and water solution. After 10 minutes of exposure to the surfactant solution, the test paper remained dry (only TYPAR WRB results shown here), demonstrating the wrap’s ability to withstand moisture intrusion after surfactant exposure.

Wrapping Things Up

Although it is never advisable to expose weather-resistant barriers to surfactants, most will be exposed despite best intentions. So, it’s best to select a wrap that is surfactant-resistant, standing up to today’s harsh chemicals and jobsite cleaning techniques. Due to the vast amount of building wraps and moisture management products on the market, it is more imperative than ever to make the right product selections so you can design and build wall systems that meet today’s high performance, durability, and moisture control standards.

Choosing a weather-resistant barrier that has the balance of all properties—bulk air and water holdout, durability, optimal permeability, and surfactant resistance—will help you provide walls and buildings with the ultimate protection, while giving you peace of mind.