Where Should Downspouts Drain? Flat Lots and Rain Barrels

Low-slope roofs and patio covers

Flat and low-slope roofs on ranch homes, patio covers and apartment buildings are the extreme case. A whole roof of water reaches just a few downspouts, so each one needs to be open, sized right and pointed somewhere useful. Our gutter installation page shows how we plan downspouts for these roofs, and our commercial gutters page covers apartment buildings and HOA properties with long, low rooflines over shared walkways.

On a new system, downspouts stay off walkways, driveways and entry steps, and the garage door and patio sides get covered first, since they take the worst splashback. On an existing house, most fixes come down to downspout extensions and redirects.

How far out is far enough

Our El Niño gutter preparation checklist says to send every downspout at least 5 feet out with an extension or splash block, so roof water stays off the foundation and away from the slab. Where five feet would cross a walkway or a driveway, a redirect around the corner usually works better than a longer pipe.

One Google review on our site says the crew diverted the rain gutter so the homeowner’s patio would not flood when it rains. That is the whole idea.

The H2OC Stormwater Program, Orange County’s stormwater education program, explains on its runoff page that the county’s storm drain system was built to prevent flooding of inland areas, and that runoff from roofs, driveways, yards and streets flows, untreated, to the Pacific Ocean through a series of creeks and channels.

The City of Fullerton’s Public Works storm drain page says urban runoff flows untreated through the storm drain system, and lists a few rules that apply right at the gutter line: do not over-water so that water flows onto the driveway or sidewalk, do not hose down the driveway or patio to the street, and do not rake or blow leaves into the street.

So when a downspout can empty onto a lawn or a planting bed a safe distance from the house, that is usually the better destination. The water soaks in instead of carrying grit, leaves and whatever is on the driveway to the curb.

Do not aim a downspout at a bed right against the slab or above a retaining wall. On a hillside lot the rules change, and our hillside gutter guide covers where water should go on a slope.

A good outlet on a flat lot

• Points away from the house, not along it.
• Lands on lawn or planting beds, not the driveway.
• Does not empty across a walkway or entry step.
• Sends no leaves or grit into the street.

1. Gutters all the way around.SoCal Water$mart requires existing gutters throughout the entire perimeter of the roof and existing downspouts. On a partially flat roof, every pitched area needs them.
2. All the water from one downspout.The barrel must be mounted so it receives all water unimpeded from a downspout.
3. A cover.It needs a cover to keep mosquitoes, rodents and debris out.
4. An overflow.It needs an overflow spigot with mosquito netting or another form of prevention.
5. Raised and steady.It should sit 6 inches off the ground on a solid foundation, and be strapped to the house if it is twice as tall as it is wide.
6. Out of the way.It should not block or restrict walkways or paths.
7. Rain only.It is for rain capture only, not tied into a graywater or irrigation system, and the water comes out by hose or bucket. The limit is two rain barrel rebates per water service address.

Reading the rebate rules

SoCal Water$mart, the regional water conservation rebate program connected to the Metropolitan Water District of Southern California, covers rain barrels from 50 to 199 gallons and cisterns of 200 gallons and up. The program page lists rebates starting at $35 per barrel, and it notes that amounts may vary by water agency and depend on available funding, so check the current terms before you buy.

Plan for the overflow, too. By the USGS numbers above, a tenth of an inch of rain on a 20 by 30 foot roof is already about 37 gallons, so a barrel under one downspout can fill early in a single storm. After that, the overflow needs the same thing any downspout needs: a destination away from the slab and off the walkway. Keep the gutter above it clear, too, because a packed trough sends water over the edge instead of into the barrel.

• Gutters on every pitched section of the roof.
• A clear trough and a flushed downspout feeding the barrel.
• A planned path for the overflow, away from the slab.
• A barrel that leaves the walkway open.

If you can safely reach a single-story gutter from a ladder on firm, level ground, run a hose down each downspout and watch where the water goes. If it backs up, the downspout is clogged. If it runs toward the house or across a walkway, that outlet needs a redirect. Leave second stories to a crew with the right ladders.

Then look for what the last rainy season left behind: a trench worn into the soil under the eave, paint flaking near the bottom of a wall, or a swollen garage door each marks a spot where water landed in the wrong place.

When to call us

If a downspout drains slowly after a flush, empties against the house, or the gutter overflows somewhere in the middle of a run, that is our work. A gutter cleaning visit flushes every downspout until water runs out the bottom. Our gutter repair crew re-straps loose downspouts and replaces damaged sections and elbows, and downspout extensions and redirects send the water where it belongs. A run over 40 feet that spills at its only outlet often just needs a second downspout.