Roof overhangs, gutters, and downspouts help to prevent rainwater intrusion into buildings. Shown here is the Ladybird Johnson Wildflower Center in Austin, Texas, which also has an extensive rainwater harvesting system.
I am continually surprised by how little emphasis the green building movement places on building science. As we examine the many priorities of green building—from land-use planning to energy efficiency, material selection, and indoor air quality—the basic science of how we design and build structures to ensure long life and healthy indoor environments should be at (or near) the top of the list.
Excess moisture is at the center of many problems relating to durability and indoor air quality—not just in homes but in all types of buildings in a wide range of climates. If we build structures that won’t rot or support mold growth, we will both increase the longevity of those buildings and reduce the health risks of living in them.
This article examines the physics of moisture in buildings and addresses design and construction strategies for (a) keeping buildings dry and (b) allowing those buildings to dry out if they do get wet. While the emphasis and examples are largely focused on houses, most of the ideas apply more broadly.