Gutters can quickly fill with ash during the first rain after an ashfall (or during ashfall if it's raining at the same time). The weight of the wet ash can cause the gutters to break away from the roof. Also, downspouts and drainage pipes connected to gutters can quickly clog. Disconnecting the downspouts and roof drains until most ash has been washed away may prevent costly repairs to a home's drainage system. In communities where roof-drainage systems spill into the waste-water system, further damage can be prevented by disconnecting the downspouts.

Note the ash that has accumulated in the "valley" between the two roof sections; such accumulations can prevent water from draining properly, which may lead to leaks in the roof.