“Think like a raindrop.”
That’s advice for design professionals from Washington State-based building envelope consultant Ray Wetherholt, PE, RRC, RWC, of Wetherholt and Associates, Kirkland and Olympia. Since founding his business in 1984, Ray has made a specialty of helping to create building envelopes that resist water intrusion, and fixing those that don’t.
Water is good at getting into walls, he says. When it does, depending on the way the building envelope is constructed , nasty problems can result.
Mold, and the litigation it brings is one of the most widely known problems. Water also can warp, decay and rust building envelope components; delaminate paint; and deposit ugly stains on interior and exterior walls.
But if you look at water intrusion from water’s point of view, Ray says, it will help you navigate a building envelope landscape that is constantly changing and evolving.
Since water follows gravity, use water-shedding designs that let water do what it wants to do – flow downhill. Don’t depend on laps that buck water or interrupt the water flow. Don’t build flat shelves, or try to catch water flowing down a wall.
“It’s really pretty simple,” Ray says, “but gets mucked up a lot for the sake of ‘the design’.”
Since water can find its way into walls as liquid, or by hitching a ride on air currents as water vapor, and then condensing when it hits a dew-point, structural walls must be air- and water-tight as possible.
And since total air- and water-tightness is not possible, building envelopes need to be able to dry out when a little water does get in.
“Designs are imperfect,” Ray says, “as is construction. So the goal isn’t a ‘perfect wall,’ but a wall that works.”
It’s when they don’t work that Ray and his fellow building design consultants get most of their business.
“As a friend of mine puts it, ‘no one invites us to the wedding,’ Ray says with a chuckle, ‘just the wake.’”
Failure to integrate wall components is one of the biggest reasons water gets into walls, Ray says. A common example is leaving out transition flashing. That error lets water penetrate at transitions points between components, such as where a deck edge or railing meets a building wall.
Architects aren’t always focused on how to tie it all together, and contractors don’t have details. “That’s what keeps guys like me employed,” Ray said.
Lack of redundancy also contributes to water in walls, he said. Relying solely on sealant or caulking, for example, will be a problem when the caulking fails in a spot or two.
On the other hand, there are systems that work, sometimes just by luck. A building can have multiple places water from outside can enter, but if it has a positive pressure, the water doesn’t go in easily.
“I remember one time a crane collapsed and sheared the exterior walls off about six stories on the North elevation of a nine-story building,” Ray said. “For awhile, the building basically had a tarp for a wall on that side. Yet, positive pressurization and facing away from the prevailing wind helped keep water from coming in.”
Whether or not you get water intrusion may depend on something as simple as which direction your weather comes from, Ray said.
In general, though, most buildings get water in the walls sooner or later, since no materials last forever. Good designs take that into account.
“I think we’re seeing more problems with new construction as buildings ‘tighten up,’ and trap moisture in the walls with impermeable vapor barriers,” Ray said. “That’s why vapor-permeable air- and water-resistive barriers are becoming such a big deal.
“And we’re building faster now, with less investment. We’re not building with durability as the end result, but budget.”
Even in that environment it’s still possible to design and construct building envelopes that work by design and not chance, Ray said.
For that to happen, everyone – design professionals to trades people – must understand that the various parts of the building envelope have to be integrated to work together to resist, shed and expel water.
The tools to do that exist, from advanced flashing systems to the latest vapor-permeable, fluid-applied air- and waterproof barrier systems.
To take full advantage of these resources, however, it helps to think like a raindrop, Ray said.
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