Gutters overflow because of clogged gutters or downspouts, too few or too small downspouts, gutters that are too small for the roof, incorrect slope, roof valleys concentrating water at one point, gutters mounted too low or too far out, or heavy debris and ice. Start by checking the downspout outlet, which causes most overflow.
The 7 causes
| Cause | How to tell | Fix |
|---|---|---|
| Clogged downspout | Overflow at one corner; dry downspout | Clear outlet and elbow; add strainer |
| Clogged gutter | Overflow along the run; plants visible | Clean and flush |
| Too few downspouts | Overflow on long runs even when clean | Add a downspout mid-run |
| Gutters too small | Overflow in heavy rain when clean | Upgrade to 6-inch gutters and 3x4 downspouts |
| Wrong slope | Standing water; overflow at the low spot | Re-hang at 1/4 inch per 10 feet |
| Roof valley | Overflow where two roof planes meet | Valley splash guard or larger gutter there |
| Mounted wrong | Water shoots over or runs behind | Reposition gutter under the drip edge |
Northwest-specific factors
Atmospheric river storms can drop a lot of rain in a few hours, and that is when undersized systems show it. Steep roofs common on newer Portland-area homes shed water fast, and valleys concentrate it. If clean gutters still overflow in big storms, the system is undersized.
Frequently asked questions
Why do my gutters overflow only in heavy rain?
Usually the gutters or downspouts are undersized for the roof, or a valley concentrates water at one corner.
Will gutter guards stop overflow?
Guards stop clogs, but they cannot fix undersized gutters or bad slope.
Need a hand?
- Gutter Cleaning: Hand-cleaned gutters, flushed downspouts, roof edge cleared and everything bagged and hauled away.
- Downspout Cleaning & Repair: Clogged, crushed or disconnected downspouts cleared and rerouted so water leaves your foundation.
- Seamless Gutter Installation: Seamless aluminum gutters formed on-site to the exact length of your roofline, in your color.