Photo by: Rodney Diaz
When builders began to insulate houses in the 1920s and 1930s, the exterior paint began to peel. Many painters concluded that insulation draws moisture and refused to paint a house if it was insulated. By 1938, the problem was common enough that Architectural Record
published an article titled “Preventing Condensation in Insulated Structures.” The author, an architect named Tyler Stewart Rogers, argued that insulation was not the problem; indoor humidity was. He proposed a two-part solution: vapor barriers and attic ventilation.
Unfortunately, Rogers jumped to prescriptive solutions without fully understanding the problem, says Bill Rose, research architect at the University of Illinois and one of our country’s most respected building scientists. Rogers didn’t account for the effects of temperature on wood siding, and he didn’t address rain leaking in, which Rose says is “the greatest source of water in building envelopes.”
Vapor barriers and attic ventilation did not stop exterior paint from peeling, much to the delight of generations of asbestos-, aluminum-, and vinyl-siding salesmen. Nonetheless, within five years of Rogers’s article being published, his recommendations had been written into our earliest building codes, and the fledgling discipline of residential building science was off to its rocky start.
Seventy years later, our houses are bigger, more complicated, more airtight, insulated to higher levels, and dependent on ever-pricier fossil-fuel energy. Hence, the stakes of building science—comfort, health, durability, and energy bills—are higher than ever. Despite that, most architects, builders, and code officials still don’t understand moisture movement through houses. To make matters worse, there’s no easy way for them to learn about it.