Roofers should not work in rainy conditions for multiple reasons: *First, the rain creates a slippery surface that is dangerous to work on. *Second, water can damage the roofing materials themselves. The wood decking can become wet or warped. This will either lead to uneven shingle installation, or the shingles will not be able to adhere properly. Both result in inefficient roofs that will not last for long. *Finally, installing a roof during the rain can lead to humid conditions that produce mold growth on the decking. If a roofer is in the middle of an installment and it starts to rain, they can continue working if the rainfall is light enough not to disrupt work or cause any of the problems mentioned earlier. In most cases, the contractor will end work for the day and schedule a time to come by and finish the project.