How Roof Runoff Works
Roof runoff is the water your roof gathers before it reaches a gutter. How area, slope and valleys shape it, and why the roof edge decides where it lands.
Category
Roof Runoff
Before water reaches a gutter it is shaped by roof area, slope and valleys. This section explains how runoff concentrates, why water sometimes runs behind the gutter, and the role of drip edge, fascia and soffit.
In this cluster
- How roof runoff works
- Roof area & water volume
- Slope & valleys
- Drip edge, fascia & soffit
- Water behind the gutter
- Overflow points
- Staining & fascia damage
Guides
Roof Runoff articles
Roof Valleys and Water Concentration
Roof valleys concentrate fast, heavy runoff at one spot on the eave. Here is why valleys overshoot gutters and the fixes that actually help.
Drip Edge, Fascia and Soffit Explained
Drip edge, fascia and soffit work together at the roof edge to hand water to the gutter. Learn what each does and what goes wrong when they fail.
How Roof Pitch Affects Runoff
Roof pitch changes how fast and forcefully water reaches your gutter. Learn why steep roofs overshoot, low roofs pond, and how slope factors into sizing.
Moss and Algae on Roofs
Moss and algae take hold on shaded, damp roofs and along runoff paths. Learn the difference, the damage they cause, and how to treat them safely.
Roof Area and Gutter Capacity
Roof area, not just rainfall, determines how much water a gutter must carry. Learn how drainage area and rain intensity size gutters and downspouts.
Gutter Apron vs Drip Edge
Drip edge and gutter apron are both roof-edge flashing, but they do slightly different jobs. Learn how they differ and when an apron fixes water behind the gutter.
What Is Kickout Flashing?
Kickout flashing diverts roof runoff away from the wall and into the gutter where a roof meets a wall. Learn why missing it causes hidden rot and how to spot it.
Flat Roof Drainage — Scuppers and Drains
Flat and low-slope roofs drain through internal drains and scuppers, not eave gutters. Learn how they work, why ponding is the main threat, and how to maintain them.