DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   Landscaping & Lawn Care (
-   -   Underground downspout questions (

garrett1812 04-23-2016 08:00 AM

Underground downspout questions
This year I would like to eliminate the downspout extensions and sump pump line in my yard, and replace with underground drainage system.

I think I will be okay just running the lines out to the back of the property and connecting to pop-up drains. At least at this stage of the project. If water gets too dense back there maybe will go back to add a dry well or something.

All of my downspouts are at the side of the house, so I will have at least one drain line on each side. The sump pump exists the house close to one side, so my first question is should I combine the sump pump discharge and the downspout discharge for the long (~75ft) run to the back of the property, or would it be better for the sump pump to be on its own? This sump pump is not very active. On the rainiest days it turns on maybe every 10-15 mins.

Second questions is on the actual trench for the drain line. I have read to use a 4" wide trencher for a 4" PVC pipe. But if your pipe is not sitting at the bottom of the new trech, when you backfill I do not think much material will go back under the pipe, so there will be a void under the pipe. Will I have to backfill to the exact depth before putting down any pipe? Or should I get a trencher with a wider cut?

Last, can I run a power line in the same trench as the drainage line? I do not have a purpose for the power yet, but maybe will add some lighting at the back of the property later. Far easier to run the power now.


AllanJ 04-23-2016 08:19 AM

Re: Underground downspout questions
The outlet line for the basement sump pump must never back up.

Water should not be discharged near the house.

Underground lines could freeze.

You would probably want relief valves in the form of pop ups at least ten feet from the house.

garrett1812 04-23-2016 08:29 AM

Re: Underground downspout questions
The pop ups will be 75 feet from the house.

oh'mike 04-23-2016 08:33 AM

Re: Underground downspout questions
Your underground sump pipe must be able to drain out completely--so forget the pop up---you do not want an elbow facing up at the end of that pipe.

Also---the sump discharge must not be piped directly into the ground pipe.
The sump discharge (1 1/2") should free fall into the larger ground pipe--with an air gap.

This is done because the ground pipe might get clogged with ice or other matter --and the pump water must be able to overflow safely to the ground to avoid having the pump piping blow apart inside the house.

If you use 4" ground pipe--add an elbow at the house--then a 4 to 5 inch bell reducer --this is your receptor (sink) and have the sump discharge flow in from above (faucet)

Yep---just like a sink and a faucet---

garrett1812 04-23-2016 08:37 AM

Re: Underground downspout questions
Good advice. Already have plans to drain the sump pump into the drain line with a gap, similar to what you described, but with a grate to help prevent debris from getting in.

But what options do I have if not using a pop-up? The elevation of the sump discharge is at least 5ft higher than where the pop up will be located.

oh'mike 04-23-2016 08:41 AM

Re: Underground downspout questions
As to supporting your pipe in the trench--do add gravel or soil under the pipe before the pipe is laid---you are right--you can't count on the back fill working it way under the pipe--it must be there before the pipe goes in.

Unless your soil is impossible to dig (California Adobe clay ,for instance) I suggest hand digging the trench---start at the high point and run water into the trench as you dig---that will let you know that the pitch is correct --if your trench is draining--the pipe laid into the trench will too.

garrett1812 04-23-2016 09:30 AM

Re: Underground downspout questions
Thanks. There is a lot of clay here, so for the 250+ ft I am happy to rent a trencher. Good tip on running water through the trench, would make it easy to find high spots.

oh'mike 04-23-2016 09:42 AM

Re: Underground downspout questions
I live 350 feet from a river--so I have lots of underground piping---

As the old saying goes--"been there, done that."

Try to 'drain to daylight' so that the pipe stays clear and flushes out completely--

Those pop ups are trouble---they freeze--allow sediment to build up inside the pipes and are a breeding place for mosquitoes

All times are GMT -5. The time now is 09:00 AM.

Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.