The complete guide
Buyer's Guide to Downspout Extensions and Foundation Drainage
The problem sitting at the bottom of your downspout
Gutters get all the attention. People clean them, guard them, and worry about them every autumn. Then the water comes down the downspout, hits a little elbow about four inches off the ground, and lands in exactly the same spot, storm after storm, year after year.
That spot is usually within a foot of the wall. A typical roof sheds a surprising amount of water in a single downpour, and most of it funnels through two or three downspouts. All of that volume soaks into a narrow strip of soil directly against the foundation.
What follows is predictable. The soil gets saturated and loses its grip. The grade that once sloped away from the house flattens out or starts tipping back. Splashback stains the siding. In older homes with block foundations, moisture works its way through and shows up as damp patches or a musty basement smell. In colder months that same saturated soil freezes, expands and pushes against the wall.
None of it happens in one night. That is the tricky part. By the time you notice, the problem has had years to build.
How a downspout extension works
The fix is unglamorous and effective. You put a pipe on the end of the downspout and move the discharge point further out.
That is the whole idea. Water that lands eight or ten feet from the house has a huge area of soil to spread into, and it has to travel sideways and downward through that soil before it gets anywhere near the foundation. By then it is diluted across a wide area and the ground can handle it.
An extendable downspout pipe does the same job as a rigid run of pipe, with one big advantage. It adjusts. This one compresses to about 3.4 ft and draws out to 16.5 ft, so you can set it to whatever your yard actually needs rather than cutting and gluing sections to fit.
The pipe has a 4 inch (10.16 cm) outside diameter, which gives plenty of room for heavy flow. It is PE with a thickened wall, rated to 10 psi, and the maker states it holds at least 10 pounds without deforming. That load figure matters more than it sounds, because it is what makes burying the pipe an option.
Who gets the most out of one
Homes on flat lots benefit most. If your ground does not fall away naturally, water has nowhere to go and simply pools where it lands. Pushing the outlet out to ten feet or more gives gravity something to work with.
Clay soil is the second big case. Clay drains slowly, so a concentrated discharge sits on the surface and spreads sideways rather than soaking in. Spreading the same water across a wider area, further out, lets it drain at a pace the soil can keep up with.
Older houses are worth a look too. Many were built before anyone thought hard about perimeter drainage, and the original splash blocks have long since cracked or shifted.
Gardeners have a different reason. Aimed at a bed or a hedge line, the runoff from one storm can water a whole section of yard for free. If that is your plan, choose the length that reaches your beds rather than the maximum.
Getting the fit right
Downspout outlets come in a handful of rectangular sizes. This kit includes two adapters covering 2 x 3 in, 3 x 3 in, 3 x 4 in and 3.5 x 4 in, which takes in the most common sizes on residential homes.
Before ordering, take a tape measure to the opening at the bottom of your downspout and note both dimensions. It takes thirty seconds and saves a return.
Installation is simple. Fit the matching adapter onto the downspout outlet, slide the extension on, and drive the supplied screws through to lock it. Eight screws come in the box. Do not skip them. A friction fit looks fine on a dry Saturday and ends up across the yard after the first serious storm.
Then walk the run before you commit. Stretch the pipe along the route you have in mind and look for low spots where water would sit. A steady fall from inlet to outlet is what you want, even if it is slight.
Choosing the length and the route
Longer is not automatically better. The right length is the one that reaches ground that already drains away from the house.
Walk out from the wall after a rainstorm and look at where puddles form and where they do not. The first place the ground clearly falls away is your target. On a sloped lot that might be five feet. On a flat suburban lot it might be twelve or more.
Three things to watch when planning the route. Keep the outlet clear of walkways and driveways, where discharge turns into ice in winter. Keep it off the property line, since dumping your roof water onto a neighbour's yard causes arguments. And keep it away from window wells, basement entries and anywhere else below grade.
If the tidy option appeals, drop the pipe into a shallow trench. The maker states it can be buried, and the load tolerance supports that. Keep the outlet end exposed and slightly lower so the line empties rather than holding water. A buried run disappears into the lawn and the mower goes straight over it.
Living with it through the seasons
The pipe is described as flexible, easy to bend and able to return to its shape with no creases or cracks. That is useful when you need to curve it around a corner or past a planter, and it is why you can compress it for mowing and draw it back out without ruining it.
The maker also describes it as antifreeze and explosion proof, built for snow and sun exposure. In practice, the one habit worth building is tipping or shaking the line out before a hard freeze so there is no standing water inside.
Cleaning is a hose job. Twice a year, pull it off the adapter, stretch it out and flush from the inlet end until the water runs clear. Shingle grit and small leaves are the usual culprits, especially if your gutters are unguarded. Wipe the outside with mild soapy water if it has gone green, and rinse it off.
While you are down there, check the screws. Freeze and thaw cycles can loosen fixings over a season, and a thirty second check keeps the connection solid.
The short version
Your gutter and downspout have done their job by the time water reaches the ground. What happens next is up to you.
This long downspout extension stretches from 3.4 ft to 16.5 ft, fits four common downspout outlet sizes with the two included adapters, and locks on with eight screws so storms cannot shift it. The 4 inch bore handles real rainfall, the 10 psi rating and 10 pound load tolerance mean it can go on the lawn or in a shallow trench, and the PE wall bends and springs back instead of kinking.
Measure your outlet, walk your yard, and set the length so the water lands somewhere it can soak away on its own. That is the whole job, and it is a good afternoon's work for the amount of grief it prevents.