Moisture measurements in single-family houses with attics containing radiant barriers

Abstract

Tests were conducted by Oak Ridge National Laboratory researchers at three unoccupied research houses in Karns, Tennessee, to determine the effects of moisture condensation on the underside of perforated horizontal radiant barriers during the winter of 1987-88. An experimental plan called for the houses to be operated at high indoor relative humidities (45 and 55% at 70/degree/F), with data concerning the attic moisture conditions collected by both visual and instrument measurements. The testing showed that moisture went through a diurnal cycle at the Karns research houses. Moisture could condense on the bottom surface of a horizontal barrier in cold (below 35/degree/F) weather, but it could also dissipate to the attic air during a normal Tennessee winter afternoon, leaving the barrier dry. In long periods of subfreezing weather, all the condensation did not vaporize, as some remained on the surface through the day. However, the testing did show that the moisture cycle occurring on a perforated horizontal radiant barrier during a typical Tennessee winter did not appear to pose any structural, wet insulation, or strained ceiling problems to the Karns research houses, even though they were operated at higher than normal indoor relative humidities. Care should be taken in extrapolating themore » observations of this experimental work to areas with prolonged periods of subfreezing weather. The diurnal moisture cycle under a barrier may be different in colder climates. Further testing of horizontal barriers in colder climates is recommended. 21 refs., 45 figs., 11 tabs.« less