Have you been seeking another way to control runoff and improve drainage around your home’s property? Installing a downspout extension might be helpful to divert rainwater away from your home’s framing and foundation, where it can cause water damage.
If your downspouts are not working effectively, they can cause your gutters to overflow and damage the ground below through erosion. If the overflowing water contacts the sheathing underneath your home’s exterior, mold, wood rot, and mildew often result.
We’ll provide professional tips on extending a downspout and attaching the appropriate drain pipe. We’ll discuss downspout extension ideas that will help you change the direction of the runoff and transport it to a safe location. Lastly, we’ll describe how to install downspout extensions correctly, just like the pros.
Types of Downspout Extensions
Downspout extension terminology can vary from region to region, but generally, there are four types:
- Splash Block (aka Splash Brick): Splash blocks are usually rectangular or fan-shaped pads designed to disburse the water from the downspout into a broader area. This allows the water exiting the downspout to splash against the durable block instead of eroding the soft ground.
- A-Style Downspout Extension: This diverts the runoff away from the downspout at a 90-degree angle to the downspout.
- B-Style Downspout Extension: B-Style extensions channel the water parallel to the building by turning it left or right.
- Offsets: This type of downspout extension changes the location of the downspout opening without affecting the direction of the water flow.
Benefits and Drawbacks of Downspout Extensions
Here are a few of the benefits and drawbacks of using downspout extensions:
- Prevents ground erosion
- Reduces mold and mildew growth
- Helps avoid wood rot
- Prevents flooding
- Reduces clogging, adding years of life to the gutter system
- Additional expense
- More maintenance
- Can be a time-intensive project
Steps and Tools for Installing a Downspout Extension
You can install a downspout extension with a few hand tools and a drill. Consider using personal protective equipment (PPE), like eye and skin protection, especially if you’re sensitive to adhesives. Also, inspect your tools, including your ladder, and ensure they are in good condition.
Here’s a list of tools commonly needed to install a downspout extension and the associated parts:
Ladder, standoff, stabilizer, or other personal protective equipment (PPE) as needed
Drill and drill bits
Line level (or laser)
Metal cutting shears or metal cutting saw
Needle nose pliers
Pop rivet gun and corrosion-resistant rivets
Elastomeric sealant (NP-1)
Optional: cordless drill and corrosion-resistant screws
Step 1: Determine the Path the Drain Will Follow
Determining how to extend a downspout can be more complicated than installing it. The easiest way to determine the path is to lay out your extension, splash blocks, drain pipes, and other components as they would lie in the path.
Is there an obstacle, like a swing set or sidewalk? Does the path slope appropriately for good drainage? Will the path require more bends and turns than an alternate path?
Generally, the drain pipe should be as straight as possible and make gentle, sloping turns instead of sharp, 90-degree turns.
When you’re satisfied that your path will work, mark it on the ground with marking paint. If some paint is still visible after marking the ground, don’t worry, as it will wash off in the next rain.
Step 2: Digging the Trench
An easy way to ensure your trench slopes are correct is to drive two stakes in the ground, one at the beginning of the trench and another at the end. You’ll want the stakes long enough to tie a string from one to the other without touching the ground. Cut both stakes the same length and make a mark 1” from the top.
Tie a string to both posts at this 1” mark and try to remove any slack. Hang a line level on the string. If the bubble on the level moves away from the end of the trench, the trench is sloping correctly.
You can dig the trench by hand, but a power trencher will make the job faster and easier, especially if your path is long or needs to be below the frost line.
However you dig your trench, keep the bottom slope gradual and consistent. Avoid humps and dips in the trench as much as possible. If you encounter a tree root or other obstacle, you can use the excavated dirt to even out the bottom of the trench.
When laying out your downspout extension, use standard angles when making turns. For example, most drain pipe fittings are designed for 22.5, 45, and 90-degree turns. If you observe these standard angles as you lay out your trench, you’ll do less digging to make the pipe fit.
Step 3: Adding the Base
Adding a coarse gravel base to the bottom of your trench can help prevent the pipe from lying directly in the mud, helping avoid clogs. Most pros install a layer of pea gravel about 2” deep, running the entire length of the trench.
Step 4: Installing the Downspout Adapter On the Downspout
Downspout extensions have a bell on one end where the opening is larger than the other (crimped end). Usually, the last 2” of the crimped end fits inside the bell on the next extension.
If you only need to add one extension, you can attach it to the bottom of the downspout using an A-style (directly away from the downspout) or a B-style extension (turning left or right). You may also need an offset extension, which is an S-shaped downspout extension that allows you to slightly offset two downspout sections that don’t precisely line up.
If your downspout extension idea includes installing multiple extensions, such as to go around a corner, try to keep the turns as wide as possible. For example, instead of using one 90-degree extension, consider using two 45-degree extensions instead. Dry fit your extension(s) to the downspout so that the last one sits on the ground at the beginning of your trench.
Next, dry-fit a downspout adapter to the end of the extension so that it lines up with the first section of your drain pipe and trench. Most pros use two PVC 90-degree sweep fittings back to back to make an “S” shape.
One end will eventually attach to the downspout adapter, and the other will connect to the first section of pipe inside the trench. Adjust the downspout adapter as needed until you get the correct angle to the pipe.
Step 5: Measuring for the Drain Pipe
If your drain pipe has a bell on one end, measure from the end of the pipe you want to keep. Measuring from the downspout adapter, measure to the next point in your path that requires a fitting or until you reach the end of the pipe.
If the distance between fittings is longer than the pipe, measure for two pipe sections. These will be connected end to end using the bell. After you’ve collected and double-checked your measurements, you’re ready to cut the pipes and begin the assembly.
Step 6: Cutting the Pipe
Most professionals use 4” Schedule 20 PVC drain pipe whenever possible, but you can use Schedule 40 PVC or corrugated pipe.
Pay attention to which pipe you purchase because each style will require its own type of fittings and are not interchangeable.
You can use either perforated or non-perforated pipe. A perforated pipe lets water inside the trench collect inside the pipe and drain away, while a non-perforated pipe collects water at one point and transfers it to another location.
If you need to split the water in two directions for better disbursal, attach a Y fitting to the end of the pipe. This allows you to send half the water in one direction and the other half somewhere else.
Cut the pipe to length as needed using a miter saw, handsaw, or hacksaw. Wear personal protective equipment (PPE) when using any tools. You can often cut corrugated drain pipe (and the fitting) with metal shears or a handsaw, so you don’t always need power tools.
Dry fit the next fitting before cutting the next section. This way, you can measure the length inside the fitting, which is the most accurate method.
If you use PVC pipe, you’ll need to glue the pieces together. If you use corrugated pipe, the fittings just twist on. If using adhesive, it’s a good idea to use PVC primer before applying the glue, as the primer will improve adhesion.
Step 7: Attaching a Downspout Adapter to the Drain Pipe
When you’re confident you’re ready to connect everything, connect the downspout extension(s) to the downspout adapter using corrosion-resistant pop rivets. If the pipe is too high or low to meet the downspout extension, just add or remove a little dirt under the pipe until it’s just right.
Step 8: Test Your Work
After the glue has had an appropriate curing time, test your new downspout extensions by spraying water from a garden hose onto your roof. Give the system a chance to fill and check the trench for water. Unless you used a perforated pipe, the trench should stay dry.
Tips and Precautions for Using a Downspout Extension
Here are a few tips and precautions to keep in mind when extending your downspouts:
- Identify obstacles, like a utility pole, in the planning stage. This will help you select the correct fittings to avoid the obstacle.
- Use Schedule 20 PVC instead of Schedule 40 PVC pipe whenever possible, as the fittings and the pipe are less expensive and easier to work with.
- Be watchful of berms or humps in your path. Make sure the pipe slopes the entire way from beginning to end.
- Adding a cleanout to your drain pipe will facilitate easier cleaning. To install one, place it under mulch whenever possible so you don’t risk hitting it with a lawnmower. Just add a T fitting to the pipe and point it up towards the opening of the trench. Next, install the cleanout, ensuring the cap is still visible above ground.
- Avoid mixing corrugated and PVC pipes if possible. The adapters can cause resistance to the water flow and cause a clog.
Now You’re Ready to Install Downspout Extensions
Drainage solutions should always be uppermost in your mind regarding the exterior of your home’s property. Downspout extensions are a great idea for improving drainage.
You can add splash blocks, A and B-style downspout extensions, and offsets, if you need them, with ease. By taking time and checking your measurements, you can dig a trench that protects your downspout extension and works great.
Installing downspout extensions is a DIY project, but it’s physically demanding work. Contact our pros for a free, no-obligation estimate if you’d prefer to leave the project to a local, qualified gutter company.