In recent years, the roofing industry has undergone another major change with the introduction of underlayment products that have significant moisture retention and permeability differences from the traditional ASTM D226, Standard Specification for Asphalt-Saturated Organic Felt Used in Roofing and Waterproofing, Type I and Type II felts. It is expected that these differences will have an effect on the performance of some roof covers. The goal is to study the wetting and drying performance under natural conditions for a minimum of two years and to observe and photograph any changes in the wood. This study includes 11 different combinations of two types of underlayment and four continuous ventilation products under four variations of wood cedar shingles. Each of the 11 sets of shingles and underlayments installed on a 6/12 slope, south-facing roof over a traditional ventilated attic in Climate Zone 5 are instrumented with temperature and moisture probes on the tops and undersides of the shingles. This data as well as ambient weather data are captured and recorded by an onsite computer every 15 min, 24 h per day. The outdoor test facility roof is more than 25 ft long from eave to ridge and has the moisture and temperature probes at three locations on each of the 11 test sections. The goal is to study the wetting and drying performance under natural conditions for a minimum of two years and to observe and photograph any changes in the wood. The data show major differences in wetting and drying rates that are both product and underlayment dependent. The paper includes information on the data acquisition systems and their performance as well as test facility operating parameters and the moisture retention results. Cedar is a product that is moisture sensitive and therefore provides rapid acquisition of the moisture profiles as well as expanding data on ventilation benefits shown in Oak Ridge National Laboratory ventilation research.