Extend Your Gutter Underground: No Eyesore And No Water

Driving by I watched as some of my neighbors gutter flow was washing away the dirt beneath the out spout. The grass had turned into a mud pit and was slowly eroding away even the dirt. I pulled up to my house only to see my own grass dieing which means that the future of a mud pit and little river washing away the dirt and part of my freshly mulched flower bed was bound to occur. I had to find out how, and I will share with you how I did.

The most important planning factors being your lawn slope(grade) and materials/method of installation. The cost depending on your home can be approximately $150 to $300, but working smartly and not cheaply can save you some money and get you good materials that are required to not make bigger headaches for you later. We will talk about all of this and more below.

Extending your gutter underground could be the best solution if you are planning on putting a garden bed right next to your house like we discuss here.

Materials and Planning

Depending on your environment, including your yard slope and gutter debris, it will change slightly the materials you get for your drainage system. There are several filtration systems that will clog and allow water to fill the piping going no where and this can lead to rapid degradation and freezing/bursting of pipes depending on your area. Lets start off with the design of your drainage system.

Grade

The grade or slope of your lawn can determine the direction of your drainage area. If you have natural low or dry areas then those are prime areas to allow the water to drain too.

Where do you want your drainage to go? Swaths, basins, and natural watersheds are different and similar in that they all may be slightly different in design, but they all allow the water to pool in them and disperse over time or out of sight. These natural or artificial drainage areas are lower than the rest of the property and permit the water to drain to them naturally without a significant amount of erosion or localized damage. Pick your prime location whether it be near the road, basin or other drainage system.

Now it is time to determine the slope. A 1% slope is the minimum. This means that you must go down 1 ft for every 100 ft you travel. It is unlikely that you will be traveling 100ft, but if so then you can do it! A 2% slope is prime, and in excess of a 5% slope can actually erode away the soil near the exit so be careful not to transfer you problem to another area. Below you will find a quick table to help you determine the slope based on your grade and later we will talk about how to determine what grad you have.

	1%	2%	3%
8′	1″	1.9″	2.9″
10′	1.2″	2.4″	3.6
15′	1.8″	3.6′	5.4
20′	2.4″	4.8″	7.2

Digging 12″ to 14″ down is the depth you want to go. If you go any shallower then it won’t allow you to install any gravel if required. At a minimum you want to place gravel at the places where you will put a debris trap or water. We will talk more about this later. I know the deeper you dig the more dirt you will have to move, but it will be crucial to not skimp on this as it can cause damage or clogging as your drainage system is being overrun with roots, dirt and debris.

Now lets determine your slope. Take a piece of string or anything of the sort and attach it to one of two sticks. Don’t forget to take your level. Drive the stick with the string into the ground by your gutter so that the string is flush with the ground and the other stick by destination.

Hold your string against the destination stick moving it up and down while holding your level against the string. Once you have the string level, wrap it around the stick and tie it down so it will not move. Measure the distance from the string to the ground at the destination and that will be the depth of your grade.

Using the information you have now you can determine the distance you will travel and the depth of your trench. If I dig down 12″ consistently over the travel I should retain a consistent grade(as long as my ground is relatively flat). Before you actually lay any piping it is a good idea to go over it again with a larger level to determine if your grade is constant over every part of your trench. Also, if you don’t have a larger level simply attach you small level to a 2-4 ft piece of wood that is relatively flat. Make sure it is level when you set in on flat ground and their you go.

Materials

You have a hole, now what to put into the whole. The most crucial pieces are the type of pipe installed and the use of debris traps or water drains. These are basic conceptually, but can make the difference between an efficient drainage system and a tube of water that is underground rather than above it. Lets look at the type of piping.

The two types we will discuss are corrugated pipe and white solid PVC pipe. There are pros and cons to each, but one requires you to spend a little more time carefully installing it. Either way they are installed, if not done with the proper grade you will find yourself with a pipe full of water going no where.

Corrugated pipe comes in single wall and duel wall. The duel wall can have smoother inner walls, but sacrifice some flexibility for this. Often times people believe that a smoother wall will wash away debris better than a corrugated wall. If graded properly this is not the case as the ribbed inner wall creates a turbulent flow that will pick up the debris in between the ribs washing it down to the end and provide you with the flexibility you desire if you are moving around a bend or bed.

Solid PVC pipe will effectively make it easier to determine if you have the proper grade and will hold that sloper for longer as it is more rigid. You can more easily tell if the entire piece of piping has a true slope, where as if your not careful you can develop a belly in the corrugated pipe that will retain water. It is also a bit harder to install as it requires flexible fitting to move around things and glue or other adhesives to attach these multiple sections.

Bottom line, I think that corrugated pipe is more versatile as well as cheaper. Dual wall corrugated pipe can give the best of both worlds and will require less connections but requires you to be sure of the slope the entire way. If you are not absolutely positive you can make a consistent grade than just install PVC pipe and save yourself the pain and heart ache later. PVC pipe is by no means a bad choice and might be preferred for many projects.

Buy List

• 4 “Piping – be sure to calculate the number of feet you will need then add a little for the spout and drain connections.
• Catch basin(not all come with filters, but you will need it)
• Coupling fittings(if using PVC: 90 degree connection to downspout and any other couplers)
• Glue and Primer or just silicone for certain connection applications
• T fitting
• Gravel
• Green 4″ drainage grate(circular or atrium)

Tool List

• Shovel(trench shovel is easiest)
• Wheelbarrow(definitely recommend)
• Drill(or screwdriver)
• Hacksaw(for pipe cutting)

Installation

Now that you have everything you need lets get down to business.

Mark out your path

that you already laid out with your string. This can be easily done just by using your shovel and cutting out small chunks of dirt right next to your line all the way to the end. Once marked out you can just remove the line to make it easier to get up the dirt.

Try to dig out flat pieces of sod to place it back where it was after burying your piping.

Your trench should be whatever depth you decided on to help with the water flow, standard is about 12-14″ deep and about 6″ wide to allow room for your pipe. You can lay a tarp or some type of plywood board to put your dirt on. Believe me, it helps cleanup and replacing the dirt a lot faster. Once your done digging your trench, lets get to the next step.

Now that you dug your trench, lets fit your pipe into your trench to make sure that it’s the correct size. Take your long level, and make sure you have a consistent grade with no bellies all along the length of your trench. A belly is a section of your pipe that bends into a small ditch which will allow the water to pool in that section and not drain completely out.

Install your catch basin and T fitting.

Generally speaking you want to install a catch basin around the vertical section of your gutter that will connect to the pipes. I prefer this to simply connecting the piping because it allows you to simply lift off the grate and remove your filter if you need to clean it or inspect it. You can also install catch basins in low spots of your lawn to allow surface runoff to also drain to your discharge. For smaller applications(8-15′) it may be unnecessary due to the length.

The most important factor when deciding what size of catch basin that you want to install is the size of the discharge. The size of your discharge will determine how fast your basin will drain. In heavy rain your 6″, 9″ or 12″ catch will fill to overflowing in a matter of seconds regardless of the size. If the discharge piping is insufficient to remove water from the catch faster than it receives it then your catch basin will overflow.

This does not mean that you should only buy a 6″. If you need a larger inlet area if this is going to be installed directly under your drain than it may be best to buy a 9″ or 12″. If there are any extra holes in your catch basin or filters, that can be easily fixed by using a discharge plug and silicone adhesive.

The same principal does not always apply when discussing very large drainage solutions like dry wells. Dry wells are installed in homes that receive great amounts of water and can generally contain about 50 gallons. You can allow groundwater to drain into them rapidly and then allow time for the water to dissipate into the ground around it during drier days.

Your T connection will go up to the very end where you will be installing your discharge. You’ll have to dig down another ditch inside your trench about 6 to 8 in deep. For this the deeper the better. Once your ditch is done place your T connection into the trench with one opening in the ditch, one facing a trench and one facing up. Pour your bag of gravel into the T connection I do not feel it so much so that it’s inside your drainage piping as this will catch debris.

Lay your piping

You first want to lay your piping next to the trench as you have already installed your catch basin. This will allow you measure out the proper length without any math.

If using PVC pipe you can use pretty much any hand saw or miter saw to cut it to length. Lay the piping right next to your trench lining up where you think it will need to be and  mark the cutting locations. Connecting PVC pipe to all your bends catches and filters then measure the slope on top of your pipe one more time just to make sure.

If you’re using corrugated pipe, you will walk through the same process. When placing the corrugated pipe next to the trench leave an extra 2 to 3 in onto your cut. This extra length will be inserted into the connections. Next again measure the slope of your connected system.

Now before you pat yourself on the back for a job well done, get your hoes and turn it on as high as it can go. Now spray it into your system. This will give it a nice test run before you replace all your dirt and sod only to find out that your system doesn’t quite work. Look for any holes where water is not meant to discharge or for low spots where water is pooling. Any amount of water that gets trapped inside of your gutter drainage system may trap debris or freeze during the winter damaging the system and not allowing any drainage at all. If you find any holes they can be easily patched with her silicone adhesive. Low spots or bellies must be fixed by removing that part of the system and either placing dirt back in or removing dirt depending on the problem. If you’re satisfied with how your gutter drainage system is working let’s get to the next step.

Install your gutter discharge grate

If your trench is too deep or your catch or discharge sits too far below the surface of the ground you can measure the length you need to reach the surface purchase additional 4″ size pipe and cut it to the perfect length to extend your piping to the surface. If you need to purchase more just bring your connection to make sure it fits. It really stinks to have to make many trips to the store because something doesn’t quite fit.

Now fill the dirt back in around your pipe with a slight mound. This will ensure when the rain comes and compresses the dirt slightly you won’t end up with a ditch. Place the sod back where it was and pack it down slightly with your hands. To help the soil set properly you can take your hoes and soak the ground that you just replaced.

Now you can step back and pat yourself on the back for a job well done. You finished installing your underground gutter drainage system.

Common Gutter Drainage Problems

Normally all your problems in your underground gutter drainage system will stem from something that is keeping the water from flowing. Maybe an odd angle is taking away all the velocity the water gains coming down your vertical gutter, maybe a dip or belly is causing pooling water, or maybe poor materials are causing clogs and rapid deterioration. Let’s talk about some of these and more below.

Connections and drainage filters can be your downfall

As the water comes down your gutter it gains a lot of velocity, this speed will push the water down your drainage system and discharge out. You don’t need to take all your speed away by adding an extra angle, incorrectly sized connection, or an oddly-shaped connection. While this alone may not inhibit the drainage of water, if there is a buildup of other material within the drainage piping then the water would not have enough velocity to push the debris out.

Smooth connections and limited angles will help your water slide smoothly through the drainage system. There are also some local codes that determine the number of angles your drainage system can have.

Incorrect or improperly installed filter systems

This can build up debris and inhibit flow, but making your filtering system easy to clean out can be critical as a homeowner. Having an open filtration system that can be checked buy a simple visual inspection while walking around the yard is the best method I have seen to keep your underground gutter drainage system clean.

Also, by maintaining proper water velocity it will push any small pieces of debris that get through your filtration system down the piping to the discharge. If the water does not have enough velocity to push the debris out of the discharge, it may be small enough to wash out through the stone underneath of it T connection or again by removal after a simple visual inspection.

A few indications you might look for to figure out if your drainage system has a leak or clog is an overflowing inlet or nothing coming out of your discharge during the rain. If it is a light rain you may not see a discharge because the gravel under your T connections is simply draining all the water. If you see an overflowing inlet, you likely have some type of clogged downstream that needs clearing.

When push comes to shove and your clueless with a small pond forming in your backyard just call a professional. I know you did all this work to accomplish it yourself, but sometimes it is just a simple fix that someone with years of experience can tell you over a consult minimizing the hit to your wallet…and pride.

Related Questions

What is the best place to discharge your drainage system?

How big of a drainage system do I need?