What Falling Leaves Do to Your Roof
Why leaves in the valleys and gutters matter, and what to do about it from the ground.
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Gutter & Roof Guide
How Clogged Gutters Cause Roof Leaks (And Basement Leaks Too)
A clogged gutter doesn't look like a roofing problem until the ceiling stain shows up. Here's the path the water takes, why it lands where it does, and how to stop it before the next storm.
What A Gutter Is Supposed To Do
A roof sheds a surprising amount of water. One inch of rain on a 2,000-square-foot roof is about 1,200 gallons, and a summer thunderstorm can drop that inch in an hour. The gutter's whole job is to catch that water at the roof edge and carry it to a downspout that puts it somewhere harmless, well away from the foundation.
When the gutter is clear and pitched right, all of that happens without you noticing. When it's packed with leaves, seeds, shingle grit, or a bird's nest, the water has to go somewhere else, and every "somewhere else" costs money.
How A Clog Turns Into A Roof Leak
Water in a blocked gutter rises until it spills. Some of it goes over the front lip, which you can see. The rest goes over the back edge, which you can't. Behind the gutter sits the fascia board, and behind that, the ends of the rafters and the underside of the lowest course of shingles.
Every storm, that back edge overflow soaks the fascia, wicks up under the drip edge, and wets the roof decking at the eave from below. Plywood that gets wet from underneath every week doesn't dry between storms. It goes soft, then black, and the nails holding the shingles lose their grip. On a tear-off, the eave is the first place we look for rot, and a clogged gutter is the usual reason it's there.
Water also follows the fascia sideways into the soffit and down inside the wall. That's why the stain shows up on a ceiling or an upper wall near an outside wall, sometimes ten feet from the gutter that caused it, and why people go looking for a roof leak that isn't in the roof.
Why It Gets Worse In Winter
A gutter full of wet leaves in December becomes a gutter full of ice in January. Meltwater from higher up the roof runs down, hits the ice, and freezes on top of it. That ridge is the start of an ice dam, and once it's tall enough, water pools behind it and works uphill under the shingles. The heat escaping through your attic is what causes the melting, but a clogged gutter gives the dam its foundation. We walk through the whole sequence, with a cutaway, in our guide to what causes ice dams.
The Basement Leak Nobody Blames On The Gutter
The other half of the overflow lands on the ground at the foundation, in exactly the spot the gutter was supposed to keep dry. A few hundred gallons dropped at the base of the wall in one storm saturates the soil, and a fieldstone or older poured foundation lets it through. The same thing happens when a downspout dumps within two feet of the house, even with a perfectly clean gutter.
If you get water in the basement after heavy rain and the sump can't keep up, look at the gutters and the downspout outlets before you call a waterproofing company. Extensions that carry the water four to six feet out, or a buried drain line to daylight, solve more wet basements than anything else we see.
Signs Your Gutters Are Clogged
- Water sheeting over the front edge during rain, especially mid-run rather than at a corner
- Streaks, staining, or peeling paint on the siding under the gutter
- Standing water in the gutter a day after the rain
- Plants growing out of the gutter
- A gutter sagging or pulled away from the fascia
- Ice hanging off the gutter in winter while the neighbor's gutters are clear
- A ceiling stain near an outside wall, or a damp spot at the top of a basement wall
Why Gutters Overflow Even When They're Clean
Sometimes the gutter is spotless and still spills. That's a design or installation problem, and cleaning won't fix it.
- Wrong pitch. Gutters need a slight fall toward the downspout. A run that's flat or pitched the wrong way holds water and overflows in the middle.
- Too small for the roof. A big, steep roof sends water at the gutter fast. Five-inch gutters handle most homes; larger or steeper roofs often need six-inch gutters and bigger downspouts to keep up.
- Not enough downspouts. One downspout for a long run can't drain it in a downpour. We add outlets roughly every thirty to forty feet of gutter.
- Sagging hangers. Old spike-and-ferrule hangers work loose. The gutter dips between them and the low spots overflow.
- Leaking seams. Sectional gutters have a joint every ten feet, and every joint is a future leak. That's why we install seamless aluminum gutters, formed on-site to the exact length of each run.
Most seamless gutter jobs in our area run about $3,000 to $5,000 depending on the size of the house and the material. If you're already planning new siding, the gutters come with it at no charge.
What To Do This Week
Clean them, then run a hose into each gutter and watch: water should move steadily toward the downspout and come out the bottom in a few seconds. Push on the fascia behind the gutter with a screwdriver handle; soft wood means the overflow has been going on for a while, and we replace rotted fascia and trim along with the gutter. Make sure every downspout lets out well away from the house.
If there's already a stain inside, the water has been in the wall for a while. Our roof repair crew traces where it traveled and fixes what it touched, with a 48-hour response on repair calls and a free estimate.
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Gutter and leak questions we hear most
Can clogged gutters cause a roof leak?
Yes. When a gutter can't drain, water spills over the back edge, soaks the fascia board, and wets the roof decking at the eave from underneath. Over a season that decking goes soft, the shingle nails lose their grip, and water finds its way into the soffit and the wall. The stain usually appears on a ceiling or upper wall near an outside wall of the house.
Why are my gutters overflowing in the middle?
Either there's a clog you can't see from the ground, or the gutter has lost its pitch. Gutters need a slight slope toward the downspout, and when hangers work loose the run sags in the middle, holds water, and spills there. If cleaning doesn't fix it, the gutter needs to be re-hung or replaced.
Where should downspouts drain?
At least four to six feet from the foundation, onto ground that slopes away from the house. A downspout that ends right at the wall puts hundreds of gallons against the foundation in one storm, which is the most common cause of a basement that gets wet only in heavy rain. Extensions, splash blocks, or a buried drain line to daylight all work.
Do clogged gutters cause ice dams?
They don't cause the melting, which comes from heat escaping through the attic, but they make the dam form faster. A gutter full of frozen leaves holds meltwater right at the cold roof edge and gives the ice a foundation to build on. Clean gutters going into winter are the cheapest item on the ice dam prevention list.