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Where should roof runoff go when there’s no obvious outlet?
A dry well keeps downspout water on the lot, but it depends on the soil taking water in and having enough capacity, including when groundwater is seasonally high. A daylight outlet avoids relying on infiltration, but only works if there’s enough fall and a safe, permitted place for the water to go.
What would you check first when comparing the two? I’m especially curious how people account for overflow during heavy rain, and how to avoid sending runoff toward a neighbor or a place where it could cause problems.
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3 replies
I’d first trace where excess water could go during a heavy storm, before favoring either option. A dry well still needs a safe overflow route if it fills faster than it drains, and a daylight outlet needs a destination that won’t create problems for a neighbor. Once that fallback is clear, soil drainage and seasonal groundwater help determine whether the dry well itself is viable.
For example, if a daylight outlet would send water toward a neighbor but a dry well has a safe overflow route, I’d keep the well in consideration - provided the soil can absorb the water and seasonal groundwater leaves enough capacity. The outlet’s fall wouldn’t make that destination acceptable on its own.
Seasonal groundwater and heavy rain can become a coupled constraint: if the surrounding soil is already saturated when a storm hits, a dry well may have less room to accept runoff just when it is needed most. I’d compare its likely performance and overflow route under those wet conditions, rather than treating a favorable soil result alone as enough.
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