Can a roof be reshingled in the rain?

A roof should never be reshingled in the rain, and reputable roofing contractors will not install shingles during wet weather. There are critical safety, quality, and warranty reasons for this rule. First, safety, as wet roofing underlayment and shingles become extremely slippery, creating a severe fall hazard for workers, and wet conditions increase risk of electrical hazards with power tools. Second, trapped moisture, as installing shingles over a wet deck traps water between the deck and underlayment, leading to plywood rot, mold growth in the attic, and reduced nail holding power as the wood swells and shrinks. Third, adhesion failure, as asphalt shingles rely on a heat-activated sealant strip to bond together, and this strip will not properly activate or seal on wet surfaces, leaving the roof vulnerable to wind blow-off. Fourth, sealants and roofing cements will not adhere to wet surfaces, causing flashing and valley details to fail. Fifth, manufacturer warranties explicitly require installation on a dry deck in dry conditions, and installing in rain can void the warranty. If rain begins during a tear-off, crews must immediately cover the exposed deck with tarps and stop work until the deck is completely dry, which may take 24 hours or more depending on humidity and sun.