Water hasn't changed how it enters a house, but how we deal with it as builders certainly has. Let's start with an oft-mentioned truism: All wall claddings leak. What we might think of as a house's first line of defense against the elements turns out to be relatively defenseless. Regardless of your level of craftsmanship, water is going to find its way behind whatever you cover your exterior walls with—wood, masonry, metal, or vinyl.
In the not-so-distant past, when houses were not as well insulated or as tightly built as they are today, water that infiltrated behind the siding might have stained the flower-patterned wallpaper in the parlor, but chances are, the house didn't rot.
It's a different story with today's tighter and more energy-efficient homes. We began to understand this in the early 2000s, when mold was discovered in buildings throughout the U.S. With the mold came rot. Home builders remedied some of the problems by paying attention to things like ventilation and source control, which they previously had the leisure to ignore. But more than a few needed to buy back new homes from disgruntled homeowners.
And it got worse: As further measures were taken to improve building airtightness and energy efficiency, even more rot and mold problems arose.
But there are solutions. Building science has shown us what to do with water that leaks behind wall claddings. Proper installation of a housewrap—also known as a water-resistive barrier (WRB)—preferably with a rainscreen behind the wall cladding, enables us to build resilient homes that will last for generations
The main reason that rot and mold didn't substantially affect older homes is because the water that got past the leaky siding had a chance to dry. Before the days of plywood sheathing and drywall, not to mention insulation, caulking, and other airtightness measures, air flowed more freely through the building and any water that got in dried out.
Wood doesn't rot and mold doesn't grow when wood gets wet; it happens when the wood stays wet and can't dry. And engineered-wood products (OSB in particular) don't stand up to constant wetting as well as solid-wood framing and sheathing products do.
Joseph Lstiburek, the founding principal of Building Science Corporation, has said, "Rain is the single most important factor to control in order to construct a durable building." And the architectural design of a home can influence how much rainwater lands on the walls of a building. Here are some points to consider:
--Lack of overhangs. The absence of roof overhangs in many new houses allows more water to hit the walls. Here's an analogy: Roof overhangs are like an umbrella in a rainstorm. If you don't have an umbrella, you better make sure you're wearing a high-quality raincoat, or you're going to get wet. Think of a good WRB system as being like a raincoat for the house.