As a building scientist, I never say, “I told you so.” But sometimes it’s hard.
About 20 years ago, I worked on a custom home intended to showcase natural and non-toxic building materials. One of the home’s highlights was a bathroom with stunning views of the surrounding hills. Its large, jetted tub was cantilevered over an open porch. The overhang was insulated with cotton batts and finished with tongue-in-groove pine boards.
I warned the homeowners that without a good air barrier, cold outdoor air would move through the joints in the paneling, work its way through the batts, and freeze the tub’s plumbing. My concerns were ignored. After all, I was just a local contractor, and their big-city architect assured them there was nothing to worry about. You can guess how this story ends.
Pipes freeze when exposed to sustained temperatures below 32°F. Water expands as it turns to ice; the burst pipes that result are responsible for hundreds of millions of dollars per year in insurance claims.
One of the most detailed studies I found on the mechanisms of pipe freezing and bursting is a 1996 report prepared by Jeffrey Gordon for the Insurance Institute for Property Loss Reduction. Gordon conducted experimental studies, first in a specially instrumented commercial freezer and then in a field laboratory built to simulate a residential attic. Gordon reports that pipes freeze in four distinct stages:
- When exposed to very cold air, the water in the pipe cools rapidly. Interestingly, the water may “supercool” or remain liquid several degrees below 32°F. This supercooled state can persist for hours.
Get building science and energy efficiency advice, plus special offers, in your inbox.