While inspecting thousands of Massachusetts and New Hampshire homes in the past years, I’ve run into countless homes with existing roof water drainage issues. The majority of the roof edge gutters (that do have the downspouts installed) are simply pouring the roof water right next to the foundation. This type of installation is causing the foundations to become damaged, and are causing excessive seepage at the inside corners of the basement. Installing extensions on these problematic downspouts will usually alleviate further basement seepage because the roof water is now conveyed out and away from the foundation area. The problem is, most homeowners do not like the appearance of those long ugly sloped downspout extensions installed at the outside corners of their homes. These extensions ruin the aesthetics of their beautiful landscaping and they become very bothersome when you have to guide yourself around these extensions when mowing or maintaining your lawn. There are also many situations where a walkway or driveway makes it impossible to install a downspout extension onto a vertical downspout. You obviously can’t install the extension(s) across the top of these busy areas. There is a solution (for homes without tight property lines)….This is when a Dry Well comes into play.
I’m going to explain how to properly design an efficient dry well that will take on most of your roof water, which can alleviate any problematic puddling next to your foundation and excessive seepage into your basement.
The first thing you need to do is prepare for the installation. The tools required for your dry well installation will include the following…
4” PVC Piping (Solid)
4” PVC Piping (Perforated)
PVC downspout adapter, elbows, and any other fittings, hardware and glue that is needed to connect your existing downspout to the PVC drainage pipes.
PVC handsaw or a hacksaw
Landscaping fabric (quantity will vary)
Long handled Shovel
Lots of ½ to ¾ inch Washed Stone
A Dry Well Shell with holes
Basically, you will be constructing your dry well by excavating trenches in the ground and filling them in with washed stone and PVC piping which will allow for a convenient connection from your house downspouts to underground piping which will carry the roof water into a dry well. This will allow the roof water to be conveyed away from your foundation and stored into voids in the ground without disrupting the appearance of your landscaping and blocking busy areas.
The first step you must take for your dry well installation is to make sure aluminum (or copper) gutters and downspouts are installed at all sloped roof edges of your home. I recommend not installing those cheap vinyl gutters and downspouts as they bend easily and cause more problems than their worth. Please stay away from vinyl gutters.
Ok, Lets get started. First, determine a suitable location for the dry well. It should be well away from your homes foundation and should always be located down hill from the house (A minimum of ten feet away). During a rainy day, grab your umbrella and survey the perimeter of your property to determine which direction the rainwater flows. A great location for your dry well(s) would be anywhere within an area where the water is flowing downhill. Tag these locations with stakes. These locations can not be utilized as a dry well if a high water table exists within that area.
After you’ve got your locations marked out, get a heavy duty tape measure and measure from the foundation out to the area where you would like to locate your dry well shell/pit. This measurement will determine how much PVC piping will be required for your installation. PVC Drainpipes come in 10-foot lengths and are available at your local building supply store. The 4-inch diameter pipe is best. You'll need three types of pipe: solid PVC drainpipe (with no holes), and perforated PVC drainpipe (with holes) and a PVC elbow for each location. The elbows and solid PVC piping will be installed at the downspout termination areas and will convey the roof water to the perforated PVC drainpipe, which starts dispersing water underground even before it gets to the dry well. If the pipe is going to pass underneath a driveway, consult local codes for the type of pipe to use. It must be stronger than standard PVC pipe.
Now lay burlap alongside the area that will be trenched. It serves as your rough guide for digging a straight trench and provides a handy location to shovel the dirt onto, making your cleanup and re-filling the trench much easier.
After contacting and verifying utility locations with Dig Safe, use your long-handled shovel to start digging the trench to a depth of about 12 inches. Pile the dirt on top of the burlap as you work. If you are digging through a great looking well established lawn, you can neatly edge both sides of the trench first, using a spade, a turf cutter, or a square-blade shovel. If you work very carefully, you’ll be able to remove sections of lawn, and then replace them sections over the excavation when the trench has been filled in. An alternative would be to reseed the entire disturbed area.
Install the downspout adapter, elbows, and any other fittings needed to connect your existing downspout to the PVC drainage pipe. If you must cut small sections of pipe to do this, use a handsaw designed for cutting PVC pipe or a hacksaw. Depending on the circumstances, you may have to screw or glue above-grade joints together to prevent them from disconnecting. Joints below grade do not have to be fastened.
Now start laying the solid lengths of PVC pipe into the trench. Place a level on top of the pipe in several locations and check to make sure it’s sloping away from the house. The pipe should slope at least 1/4 inch per foot of run (one end of a 10-foot pipe should be 2 1/2 inches lower than the opposite end). Install any remaining solid lengths of PVC pipe as necessary, then cover the pipe with the dirt from the burlap area and tamp it down good.
Continue digging the trench for the perforated sections of pipe. This section of the trench must be a few inches deeper to allow for a two inch stone bed. Before installing any perforated pipe, line the trench with landscaping fabric (make sure you overlap all edges), then pour two inches of washed stone into the base of the trench.
Lay the perforated pipes into the trench, (on top of the washed stone with holes always facing down) maintaining that 1/4-inch-per-foot slope. Now wrap landscaping fabric over the top of the pipe and let it drape over the sides with all fabric edges overlapping. The landscaping fabric will prevent dirt from getting into and clogging the holes in the bottom of the perforated pipe. Now pour additional stone around the sides of the perforated pipe, making sure the fabric stays against the pipe. Now you can cover this piped area with dirt and tamp it down. Important: Leave the last perforated pipe connection off, so you can connect it to the dry well shell once it’s installed into the pit.
Now dig a nice deep hole for the dry well at your established location. You never want the bottom of your dry well to be less then two feet above the peak water table level, which is usually at its highest in Spring. Otherwise, the dry well will be useless and simply become a repository for ground water. So if you’re digging and a water table starts to accumulate in the hole, you’re dry well location is not going to be suitable.
In Massachusetts, the top of your dry well should be well recessed 36 to 42 inches below grade (maximum depth of 10 feet) so the draining water doesn't freeze and back up through the drainage pipes and end up back at the foundation area. This will defeat the purpose of your dry well. The width of the pit should be 4 to 5 feet square. If you have underground utilities nearby, the top of the dry well must be below this level (at least three to four feet below grade, typically).
Once you get the pit dug to size, smooth it out and remove any loose dirt. Then carefully line the entire hole with landscaping fabric. Drape plenty of fabric out to the top of the hole to assist holding it in place. You will also be using this draped area last, to cover the stone. (Again, don’t forget to overlap the fabric at all edges). Then pour in a layer of washed stone 4 to 6 inches deep and smooth it out.
Set the dry well shell into place and connect that last section of the PVC (perforated) drainpipe. The end of the pipe should extend about 6 inches into the shell. Then install the overflow valve according to manufacturer's instructions. A perforated observation pipe can be inserted vertically into the dry well to allow for future inspection and maintenance. Now attach the dry well cover to the shell.
Fill in around the whole dry well shell with additional washed stone. Depending on the type of dry well and the size of drainage gravel you are using, you might also have to wrap the shell with landscaping fabric before back filling with the gravel. (Be sure to follow the manufacturer’s recommendations). Now take the draped fabric at the top of the hole and wrap it over the top of the washed gravel, then back fill the dry well area with a minimum of 1-foot soil cover over the top and then finish back filling the remaining piped section with dirt and tamp it all down.
Remove any excess dirt for reuse elsewhere. Reseed and water the bare areas as necessary or if you saved sections of grass, you are now ready to replace that grass now.
You can now you can relax during those heavy rain showers.
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I just wanted to write and thank you very much for doing our inspection today. You really took an awful lot of extra time to explain things to us. It was a huge help and by far my favorite part of this whole home-buying process. In addition to drawing our attention to the major projects that need to be undertaken right away or in the near future, I was glad that you were also so thorough as to point out smaller things and provide suggestions for fixes that we'd be able to do ourselves. Thanks again for all your effort. I'm finding your "Know Your Home" book a great source of information along with your report. I'll no doubt have some questions for you at some point and really appreciate your willingness to answer them. Have a great rest of your weekend!