Gutters overflowing when it rains: causes, and what's DIY vs plumber

Steps

1. Note where it overflows. Overflow along a whole run points to a full gutter. Overflow at one spot, such as a corner or the low point beside a downpipe, points to that downpipe.
2. Look for leaves and plants. If you can see debris above the gutter edge from the ground, or seedlings growing in it, it's a cleaning job.
3. Check the downpipe. Follow the downpipe guide. A blocked downpipe makes a clean gutter overflow.
4. Sight along the gutter for sag. Gutters are set with a slight fall towards the downpipes. A dip in the middle, brackets pulling away, or water still sitting in the gutter a day after rain means it has lost its fall.
5. Watch the valleys. Where two roof slopes meet, water concentrates. In heavy rain it can shoot straight over the gutter at the bottom of a valley.
6. Notice when it happens. Some gutters have small slots along the front, so that in very heavy rain they spill outside rather than back into the eaves. A little water from those in a downpour is by design. If clean gutters overflow in every heavy storm, the gutter or downpipes may be too small for the roof, or there may be too few downpipes.

If that didn't help

• Cleaning jobs (you or me): leaves in gutters and valleys, a downpipe blocked with leaves, a pit grate clogged with debris.
• Licensed plumber: re-hanging a sagging gutter, replacing rusted sections or leaking joints, adding or upsizing downpipes, box gutter repairs, and anything in the underground stormwater drain. Gutters and downpipes are roof plumbing, which in Victoria must be done by a licensed or registered plumber. Check your plumber with the Building and Plumbing Commission.