Work gloves
Use it for: Protects your hands while digging, handling pipe, and pulling out old fittings.
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How to Replace a Buried Downspout Extension
To replace a buried downspout extension, first confirm the underground line is crushed, split, or too clogged to save, then dig it up, remove the failed section, install a matching replacement with secure connections and proper slope, and test it with water before backfilling.
This is a manageable homeowner repair if the run is accessible and the damage is limited to the buried extension itself. The goal is simple: move roof water away from the house again without leaks, low spots, or loose connections underground.
Before you start: Match the replacement part to your exact downspouts extension before ordering.
Safety first
- Call for utility locating before digging if there is any chance of buried electric, gas, water, irrigation, or communication lines in the area.
- Wear gloves when handling old pipe, fittings, and wet soil with sharp debris.
- Dig carefully near the foundation and do not undermine walkways, steps, or retaining edges.
- Do not leave an open trench unattended where someone could step into it.
Tools you may need
Shovel or trenching shovel
Use it for: Lets you expose the buried extension without tearing up more yard than necessary.
Shop trenching shovels
Tape measure
Use it for: Helps you match the replacement length and check the trench slope.
Shop tape measures
Hacksaw or PVC pipe saw
Use it for: Cuts replacement pipe or fittings cleanly if the new section needs trimming.
Shop PVC saws
Utility knife
Use it for: Useful for trimming corrugated drain pipe and cleaning rough edges.
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Garden hose
Use it for: Used to flush and test the new buried extension before you bury it again.
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Step-by-step fix
Step 1: Confirm the buried extension is the part that needs replacement
- Watch what happens during rain or run water into the downspout with a garden hose.
- Look for water backing up at the downspout, bubbling out of the ground, pooling near the foundation, or disappearing into a section of yard where the buried line likely runs.
- Check the above-ground downspout first and clear any visible blockage at the elbow or inlet so you do not replace an underground line for the wrong reason.
- Probe the suspected run by hand where the soil is soft or sunken to spot a crushed or collapsed section.
If it works: You have good reason to believe the buried downspout extension is split, crushed, disconnected, or too blocked to restore reliably.
If it doesn’t: If water flows freely through the buried line and exits well away from the house, the problem is likely elsewhere, such as gutter overflow, grading, or a clog in the upper downspout.
Stop if:
- You find the drainage problem is actually caused by foundation settlement, major yard grading failure, or a shared underground drain system you cannot trace safely.
- You suspect buried utility lines in the dig area and have not had the area marked.
Step 2: Lay out the new run and expose the old extension
- Mark the path of the buried extension from the downspout connection to the discharge end.
- Dig carefully along the line, starting at the downspout end and working toward the damaged section or outlet.
- Set aside sod and topsoil separately if you want a cleaner yard repair afterward.
- Expose enough of the old extension to remove it and to make solid connections on both ends of the replacement section.
If it works: The old buried extension is exposed far enough to remove and replace without forcing joints or guessing at the route.
If it doesn’t: If you cannot find the line where expected, uncover the outlet end and work backward until you locate the buried section.
Stop if:
- The trench fills with water immediately, the soil walls keep collapsing, or you uncover hidden damage that extends under hardscape, a footing, or another structure.
Step 3: Remove the failed section and match the replacement
- Disconnect the old buried extension from the downspout adapter, elbow, or coupler at each accessible end.
- Lift out the damaged section and inspect it for crushing, root intrusion, split seams, or separated joints.
- Measure the removed section and compare diameter, shape, and connection style to the replacement part.
- Trim the new buried downspout extension as needed so it fits without bowing, stretching, or pulling the downspout out of alignment.
If it works: The old section is out, and the new buried downspout extension matches the size and connection style of the existing drain path.
If it doesn’t: If the replacement does not match the existing pipe or fittings, pause and get the correct size or the proper adapters before installing it.
Stop if:
- The remaining underground pipe is brittle, misshapen, or failing in multiple places, which means a short replacement will not hold for long.
Step 4: Install the new buried downspout extension with steady slope
- Set the new section into the trench and dry-fit all connections before securing anything permanently.
- Aim for a consistent downhill path away from the house so water does not sit in a low spot.
- Reconnect the new section to the downspout side first, then connect the outlet side or downstream section.
- Seat each joint fully so the line stays aligned and does not separate after backfilling.
- Pack a little soil under the pipe where needed to support it evenly instead of leaving unsupported spans.
If it works: The new buried extension sits securely, lines up with the existing run, and slopes away from the house without obvious dips.
If it doesn’t: If the pipe rocks, sags, or pulls apart at a joint, reset the trench bottom and refit the section before moving on.
Stop if:
- You cannot create a downhill run away from the house without rerouting the drain or changing the discharge location.
Step 5: Test the new line before backfilling
- Run a garden hose into the downspout or top connection for several minutes.
- Watch the full exposed run for leaks, joint separation, standing water, or slow movement through the line.
- Check the discharge point to make sure water exits where it should and does not wash back toward the foundation.
- Make any alignment or connection corrections now while the pipe is still exposed.
If it works: Water moves through the new buried extension cleanly, with no visible leaks or backup, and exits away from the house.
If it doesn’t: If flow is still slow, inspect the downstream section or outlet for another blockage before burying the new pipe.
Stop if:
- Water backs up even with the new section installed, which points to a clog or failure farther downstream.
Step 6: Backfill the trench and confirm the repair in real use
- Backfill around the pipe in layers, pressing soil in gently so you do not knock the joints loose.
- Restore the topsoil and sod, keeping the finished grade slightly mounded because fresh soil usually settles.
- Run one more hose test after backfilling to make sure the line still drains properly.
- During the next good rain, check that water enters the downspout, moves underground, and discharges away from the house without pooling near the foundation.
If it works: The trench is restored, the buried extension stays connected under soil, and the system handles real runoff without backup or soggy ground near the house.
If it doesn’t: If the area still stays wet after rain, look for a downstream blockage, poor yard grading, or an outlet that is too close to the house.
Stop if:
- The ground keeps sinking over the trench, the pipe shifts after backfilling, or water still surfaces near the foundation after a proper test.
Replacement Parts
Find a buried downspout extension on Amazon
Match the replacement part to your exact downspouts extension before ordering.
As an Amazon Associate I earn from qualifying purchases. Repair Riot may earn a commission at no extra cost to you.
Verify the repair
- Water enters the downspout and disappears into the buried extension without backing up.
- No water leaks out of exposed joints during hose testing.
- The outlet discharges water away from the house.
- After rain, the soil near the foundation stays noticeably drier than before the repair.
FAQ
How do I know if the buried downspout extension needs replacement instead of cleaning?
If the line is crushed, split, disconnected, or repeatedly clogs because it has sagged or collapsed, replacement is the better fix. If it is intact and just blocked with debris, cleaning may be enough.
Can I replace only one damaged section?
Yes, if the rest of the buried run is still solid and the connections can be made securely. If multiple sections are brittle, crushed, or poorly sloped, replacing more of the run is usually smarter.
How much slope should a buried downspout extension have?
It should keep a steady downhill path away from the house. The main goal is to avoid flat spots or dips where water can sit and collect debris.
What usually causes a buried downspout extension to fail?
Common causes are crushing from traffic or settling soil, separated joints, root intrusion, and long-term clogging that leaves water sitting in the pipe.
Should I test the line before backfilling?
Yes. A hose test before backfilling is the easiest way to catch leaks, bad joints, or a downstream blockage while the pipe is still easy to reach.