How Can Builders Avoid the Detrimental Effects of Wind-Driven Rain?

When it comes to maintaining a building’s integrity and longevity, protecting the building from factors that contribute to moisture-related issues is key. How do moisture-related issues materialize to begin with?

According to research, wind-driven rain on a building’s façade is considered one of the largest sources of moisture² and, most commonly, moisture is the number one cause³ of structural deterioration. When moisture gets into the wall, it can cause serious damage that can lead to extensive and expensive repairs, maybe even rendering the building uninhabitable.

Significant effects of moisture-related issues on a building’s performance

 For starters, moisture intrusion leads¹ to mold growth, gradually degrading the integrity of a building’s envelope to the point of structural failure. Other moisture-related issues include:

• Damage done by insects and other pests attracted to moist environments
• Rot
• Degradation or complete failure of water-sensitive materials
• Damage and peeling of paints, varnish, and other coatings
• Corrosion of metal materials, including roofing, metal studs, fasteners, wiring or coils
• Re-emulsification of water-based adhesives, particularly in flooring and wall coverings

Water-Resistive Barriers (WRB) form an integral part of a good water management strategy that helps prevent moisture-related issues.

Three stages of rainwater penetrations on buildings

To provide some context, it’s important to highlight the stages by which rainwater penetration on buildings occurs. Research² indicates that there are three stages of rainwater penetration into a building:

1. Rainwater impinging on the building’s façade driven by wind;
2. Rainwater impinging on the surface and penetrating into the building’s envelope through defects;
3. Rainwater in the envelope that either evacuates or remains trapped

Getting ahead of the issues associated with wind-driven rain starts by choosing the right WRB system

Steve Thomas, of Steve Thomas Builders, is no stranger to the effects of wind-driven rain on buildings, and the havoc it can potentially wreak on the integrity and longevity of a structure. This was evident during a recent project of his, a small private library on a sea island in Maine, – an area known for extreme weather and wind driven rain. Steve wanted to ensure that his building stands the test of weather and time.

With these severe conditions in mind, Steve was on the lookout for an effective WRB for his current project, a small, freestanding, highly finished, very precise hybrid timber frame library on an exposed site on an island in Maine. “We regularly see 70 to 100 MPH winds driving torrential rain,” says Steve. “In our weather conditions you have to expect that water will find its way into roof and wall systems – in spite of the most careful detailing—so making sure that these systems can dry both to the inside and to the outside is critical.  Back in the day, we used two layers of #15 felt paper and put our eastern white cedar sidewall shingles right on top. But, felt paper isn’t what it used to be, and I wanted to be fully confident about the integrity of my wall and roof systems.”

So Steve reached out to building scientist Joe Lstiburek for some advice. Joe recommended a wall and roof cladding system using DELTA®-VENT SA, a vapor permeable, self-adhered, durable WRB, topped by a plastic rainscreen product, with the exterior cladding on top of that. For the roof, Steve used a synthetic shingle product that resembles cedar, and for the sidewalls he used eastern white cedar shingles.

Because DELTA®-VENT SA was not yet widely available in Maine, Steve called Matt Risinger, who was happy to put Steve in touch with the company.  I needed the product ASAP” says Steve, “and Alain Stanislas, Technical Consultant & Territory Sales Manager for Dörken, based in the Boston area, grabbed a couple rolls and drove them up to Maine! That’s service!”

Beyond the water-resistive barrier

DELTA®-VENT SA has three layers, with the two outer layers composed of a high strength spun-bonded has a full surface coating of a high tack adhesive that bonds to common building materials, making it an effective weather barrier. DELTA®-VENT SA is also a part of a full system of accessories including flashing, tapes and adhesives that are specifically designed to work together. Steve benefited from using this full system, and added “All of the accessories, flashing and tapes in the DELTA®-VENT SA system are designed to work together and bond so you don’t have to worry about some strange interaction between one product and another. It is apparent that engineers at Dörken purposefully designed and formulated these products so that they all worked together and adhere.”

“Building and renovation is all about “challenges and solutions” to building problems. Selecting the right product to address the specific challenges of your project is essential to the performance, longevity, and low maintenance of the building. It’s key to remember that it isn’t a one-size-fits all proposition.

I was impressed with the heft of the DELTA®-VENT SA, it was like putting canvas on the building. Once applied to the primed substrate, we tried to rip it off just to see how well it stuck and we couldn’t get it to release. It was part of the wall and roof system and I was confident that water wasn’t going to get behind it.

The other issue we face in our extreme weather conditions is air infiltration, not just because of the moisture issue, but also because the high wind conditions we face here on the island create positive pressure on the weather side of the building and negative pressure on the lee side. Any porosity in the envelope will help to draw moisture into the wall and roof system.

The beauty of a good WRB is that, when installed as part of an air barrier system, they work to resist movement both out of and into the building. Fundamentally, the right WRB should be vapor permeable, air tight, and water tight. That said, a combination of good design and a critical understanding of the types of products used when designing a building is important to prevent structural issues in the first place.

 

Footnotes:

1. How and why building envelopes fail, from a building forensics expert by Mark Baker, President of IBA Consultants: https://www.bdcnetwork.com/how-and-why-building-envelopes-fail-building-forensics-expert
2. Wind-driven rain and its impact on building envelopes by Hua Ge and Paul Fazio Concordia University: https://www.kuleuven.be/bwf/projects/annex41/protected/data/CON%20May%202004%20Paper%20A41-T3-C-04-5.pdf
3. Masonry and Moisture—What is the Worst That Could Happen?: https://www.buildingsolutions.com/industry-insights/masonry-and-moisture-what-is-the-worst-that-could-happen