A downspout dumping roof water at the corner of the house is the single most common cause of basement water problems. The fix is moving that water further away. Downspout extensions and rain barrels both connect to the bottom of downspouts and route water somewhere other than directly against the foundation. They are not equivalent solutions, though. This guide separates which one to install based on what problem you actually have.
How much water is moving here
A 1000 sq ft roof section receives about 600 gallons of water per inch of rainfall. A 2 inch rainstorm produces 1200 gallons through that one roof section. If the roof drains to two downspouts evenly, each downspout discharges 600 gallons during the storm.
That 600 gallons coming out of a downspout in 30 minutes is enough to saturate the soil immediately around the downspout discharge point. If that point is within 3 feet of the foundation, the saturated soil holds water against the basement wall. Hydrostatic pressure pushes the water through any crack, joint, or capillary pathway in the wall. Basement seepage results.
The fix is moving the discharge point far enough away that the soil saturation does not reach the foundation. For most residential soils that distance is 6 to 10 feet from the house.
Downspout extensions: the basic fix
Downspout extensions attach to the bottom of the downspout and route water away from the foundation. Common types:
Flexible vinyl extensions (also called downspout flippers): inexpensive (10 to 20 dollars), can be lifted out of the way for mowing, but degrade from UV in 3 to 7 years. Best for short extensions (3 to 4 feet) on the visible side of the house.
Rigid PVC drain pipe (Schedule 40 or thin-wall corrugated): 30 to 60 dollars per downspout for materials. Lasts 15 to 25 years. Best for longer extensions (5 to 10 feet) where the pipe can be routed across landscaping to a discharge point.
Buried drain tile: 4 inch perforated PVC pipe in a gravel-filled trench, sloped 1 to 2 percent away from the house. Most labor-intensive (250 to 500 dollars per downspout for materials and labor) but most durable (30 plus years) and entirely hidden. Best for long runs (15 to 50 feet) to a daylight discharge at the property edge or to a dry well.
The discharge point should be:
- At least 6 feet from the foundation
- On natural downslope away from the house
- Onto a splash block, gravel pad, or vegetated swale (not bare soil that will erode)
- Not directed toward neighboring properties
A downspout extension is the most cost-effective single improvement for any house with basement seepage or foundation water concerns. The 30 to 60 dollar materials cost prevents thousands of dollars in foundation repair if a recurring water issue is starting.
Rain barrels: a different purpose
Rain barrels are 50 to 80 gallon barrels (most commonly 55 gallon repurposed food-grade plastic) that capture downspout water for later use. The barrel sits on a stand to provide gravity head for a garden hose connected at the bottom.
The math from earlier matters here. A 1000 sq ft roof section produces 600 gallons per inch of rain. A 50 gallon barrel captures less than 10 percent of that. The remaining 90 plus percent bypasses the barrel through the overflow outlet. If the overflow discharges next to the foundation, the rain barrel has made the water problem slightly worse than no barrel at all (now the foundation gets all the same water it would have, just routed through an extra fitting).
What rain barrels do well:
- Reduce municipal water use for gardens when stored water is used for irrigation between storms
- Slow the rate of runoff during light rains, which helps in regions with combined sewer systems and stormwater fees
- Provide on-demand chlorine-free water for plant watering
What rain barrels do not do well:
- Manage storm runoff during meaningful rainfall events
- Protect basements from seepage (the overflow routing has to do this, not the barrel itself)
- Provide enough water for lawn irrigation (a 50 gallon barrel waters a small vegetable garden but not a yard)
The right setup if you want both
Most homeowners want both: stop water from hitting the foundation, and capture some water for the garden. A combined setup:
- Install a rain barrel on the downspout closest to the garden
- Route the rain barrel overflow through a flexible drain pipe to a buried drain or splash block at least 6 feet from the foundation
- Add downspout extensions (rigid PVC or buried drain tile) to the remaining downspouts, routed 6 to 10 feet from the foundation
- Use the rain barrel for garden watering between storms
The rain barrel captures convenient garden water from one downspout. The overflow routing and extensions on other downspouts handle the foundation protection. The combined setup costs 150 to 400 dollars in materials depending on the number of downspouts and length of extensions.
Installation order
If installing both, set up in this order:
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Plan the discharge points. Walk the yard during a rainstorm if possible to identify natural drainage paths. The downspout extensions should follow natural slope, not push water uphill.
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Install downspout extensions first. They are the more important component for foundation protection. Cut the existing downspout 8 to 12 inches above grade. Install an elbow and run the extension to the discharge point. Glue PVC joints with appropriate cement. Slope the extension at least 1/4 inch per foot away from the house.
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Add rain barrels on selected downspouts. Cut the downspout above the barrel inlet height. Install a downspout diverter that routes water into the barrel when it is below capacity and bypasses to the regular downspout when full. Connect the overflow to the existing downspout extension.
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Test with a garden hose. Run water down each downspout and verify the discharge ends up at the intended location with no pooling near the foundation.
Splash blocks and erosion
The discharge end of any extension or overflow needs a stable surface to spread the water over. Bare soil at the discharge point erodes within a season and creates a small gully that worsens over time.
Splash blocks (concrete or plastic, 2 to 3 feet long with a slight basin) cost 8 to 20 dollars and spread the water output over a wider area. Place at the end of every extension. For longer extensions running to vegetated areas, a 2 by 2 foot pad of river rock works as well as a manufactured splash block.
See the methodology page for our drainage evaluation approach. Pair this guide with the french drain installation article and the outdoor faucet installation guide for a complete outdoor water management sequence.
Frequently asked questions
Do downspout extensions actually prevent basement water?+
Yes, when sized and routed correctly. The single most common cause of basement seepage is downspouts dumping roof water within 3 feet of the foundation. Extending each downspout 6 to 10 feet away from the foundation, with the discharge end pointed downslope, moves the water far enough that it does not soak through the soil and reach the basement wall. The fix solves about 70 percent of residential basement seepage cases. The remaining 30 percent involve groundwater intrusion or hydrostatic pressure that requires interior drain tile or exterior waterproofing.
How much water does a typical rain barrel actually hold?+
Standard residential rain barrels hold 50 to 80 gallons. A 1000 sq ft roof generates roughly 600 gallons of runoff per inch of rainfall. In other words, a 50 gallon barrel fills completely from less than 1/10 inch of rain on a typical roof. The remaining 90 plus percent of the rainfall during any meaningful storm bypasses the barrel through the overflow outlet and goes wherever the overflow directs it. Rain barrels are useful for garden irrigation between storms but do almost nothing to manage storm runoff. They are not a substitute for proper downspout routing.
Where should the overflow outlet of a rain barrel go?+
The overflow must be routed away from the foundation, same as a regular downspout would be. Connect a 4 inch flexible drain pipe to the overflow outlet on the barrel and run it 6 to 10 feet downslope to a splash block or to a vegetated swale. Without proper overflow routing, a full rain barrel discharges excess water at its base directly next to the foundation, creating exactly the problem the system is supposed to prevent. The overflow setup is mandatory for proper rain barrel installation, not optional.
Can I connect multiple downspouts to one rain barrel?+
Technically yes, but practically the barrel fills in even less rain. A single 1000 sq ft roof section already overwhelms a 50 gallon barrel in 1/10 inch of rain. Connecting two downspouts means the barrel fills in 1/20 inch of rain. Beyond that point all additional rainfall goes to overflow anyway. Multiple downspouts to one barrel adds complexity without benefit. Better setup: one rain barrel per downspout, with each barrel's overflow routed away from the foundation. Or use cisterns (200 to 1000 gallons) if substantial rainwater capture is the goal.
How long does a downspout extension last?+
Vinyl flexible extensions: 3 to 7 years. The plastic becomes brittle from UV exposure and cracks. Rigid PVC drain pipe (Schedule 40 or thin-wall corrugated): 15 to 25 years. The pipe stays flexible enough to handle minor settling without cracking. Buried drain tile (4 inch perforated PVC in a gravel-filled trench): 30 plus years. The buried system is the most durable option but requires digging. For most homeowners the right balance is rigid PVC above-ground extensions running to a splash block or to a buried French drain at the property line.
