Gutter overflowing in heavy rain? Here is what is usually going on

A gutter overflowing in heavy rain is one of the most common calls we get once storm season starts in Melbourne. Sometimes it is a nuisance: water sheeting off the front of the house onto a garden bed. Sometimes it is serious: water running backwards into the eaves, down inside the wall, and showing up as a stain or a puddle inside. The fix depends on why it is overflowing, and that is not always obvious from the ground.

This guide covers how Melbourne storms test gutters, the difference between blocked and undersized gutters, what you can safely check yourself, and when to call someone.

How Melbourne storms test gutters

Melbourne's rain is not usually heavy for long, but late spring and summer bring short, intense storms. A thunderstorm can drop a large amount of rain in a few minutes, often with wind driving it sideways. Gutters that cope with a steady winter drizzle can be overwhelmed in a summer downpour.

Storm season also follows months of leaf fall, spring growth and pollen. Gutters that were clear in autumn can be half full by November. Add strong wind bringing down more leaves and twigs during the storm itself, and outlets block at exactly the moment they are needed most.

Blocked or undersized

Most overflowing gutters fall into one of two groups.

Blocked gutters. Leaves, moss, grit washed off the roof, and debris from overhanging trees. The gutter might be perfectly sized, but water cannot get to the downpipe. Signs of a blockage include:

• Overflow from one spot, often near an outlet or a corner
• Plants growing in the gutter
• A downpipe that barely flows in rain, or drips for hours afterwards
• Overflow that has started recently, on a gutter that used to cope

Undersized gutters. The gutter is clear, but it simply cannot carry the water arriving. Signs include:

• Overflow along a long stretch of gutter, even when clean
• Overflow where a valley pours a large volume of water into a short section
• Overflow that started after an extension added more roof draining into the same gutter
• Too few downpipes for the length of gutter

Some gutters are both: slightly undersized, and then partly blocked, which tips them over.

Why overflow can come inside

Many Melbourne homes have gutters fixed so the back edge sits close to or level with the top of the fascia. When the gutter fills, water can spill over the back edge, into the eaves, and down inside the wall cavity. The first sign might be a stain on an internal wall or ceiling near an external wall, a damp skirting board, or paint bubbling. Box gutters, which sit inside the roof line, are worse again: an overflow goes straight into the ceiling.

What you can check from the ground

Stay off the roof and off a ladder in wet weather. From the ground, during or after rain, look for:

• Where exactly the water comes over, and whether it is one spot or a long stretch
• Whether downpipes are flowing strongly during rain
• Plants or leaves visible in the gutter line
• Gutters sagging or tilted, so water pools rather than runs to the outlet
• Water marks or staining on the fascia and eaves lining
• Rust spots or drips through the bottom of the gutter
• Trees overhanging the roof
• Inside: stains near external walls, especially below where you saw overflow

Take photos or a short video of the overflow during rain if you safely can. It helps a roofer see exactly what is happening.

Our storm season checklist in News covers the rest of the roof, from ridge capping to valleys, and is worth reading alongside this one.

What a roofer does about it

We get on the roof and look along every gutter run, into each outlet and down the downpipes as far as we can see. We clear and flush the gutters, which shows straight away whether water runs to the outlets or sits. We look at what is feeding the gutters: moss washing off the tiles, a valley dumping too much water into one corner, or cracked tiles along the eaves. Those roofing causes we fix. Everything is photographed.

If the gutters were only blocked, clearing them is the fix, and keeping the roof clean stops them refilling so fast. If they are rusted out or too small for the roof, you get photos and notes showing which sections and why.

When a licensed roof plumber is involved

In Victoria, installing new gutters, adding downpipes, resizing outlets and work on stormwater drains are plumbing work, carried out by a licensed plumber. If your gutters need replacing or resizing, that is the work involved. If water is backing up from a blocked stormwater drain below ground, that is a job for a plumber too. The inspection photos still help, because they show where the problem actually is.

Before the next storm

• Clear gutters, outlets and downpipes, especially under trees
• Clean the roof if moss is washing into the gutters
• Trim branches that overhang the roof
• Check that downpipes flow freely after the next rain

Get it checked

If your gutter keeps overflowing in heavy rain, we will get up there, clear it, find out why and photograph what we find. The inspection is free. Call 0420 541 479 or send a quote request and we will call you back within 2 hours, Mon to Sat, 7am to 6pm. If water is coming inside during a storm, emergency call outs run 24/7.