Because of performance problems with hardboard siding in southern Florida, the U.S. Department of Housing and Urban Development (HUD) proposed a local standard requiring prefinishing of siding and priming of all siding surfaces, including the back. However, the effectiveness of these practices was questioned. To determine if back-priming or factory finishing improves durability and performance of hardboard siding, we installed factory-finished and factory-primed siding on two buildings in southern Florida. The buildings were identical except that one had gutters and no overhangs and the other had overhangs and no gutters. Half the siding was back-primed and half was not. Moisture content, temperature, and air pressure difference across the siding were continuously monitored for 2 years. Condition and thickness of siding boards were recorded every 3 months. After removal from the buildings, siding was inspected and final moisture contents were determined. The siding was in excellent condition after about 2Â years of outside exposure. There was no evidence that back-priming the siding reduced its in-service moisture content. Whether the siding was from the overhang building or the guttered building did not seem to make a difference, but inspection of the windows and final moisture contents of the trim strongly suggested that overhangs provided additional protection on the gable ends (gutters were only present on the sidewalls).