Downspout drainage

[CAMAN]

I have a part-time job doing maintenance at a local business. One of the things they have asked me to look into is a way to get rid of the old bent up gutters that extend 8ft into the yard and no longer work and replace them with an underground system to prevent the washout that happens after a big rain. I am working with a 30,000 sqft flat roof with nine downspouts along the back of the building.

Like always, the owner wants the cheapest solution possible.

I have done some research and come up with a solution I think will work but would like to make sure from someone more knowledgable in this stuff before we start digging.

The plan is to cut the downspouts 2ft above ground level, attach the proper 4x3 to 4inch PVC downspout adaptor and a length of 4in PVC pipe down to a long sweeping 90deg elbow. Attached to that would be a 10ft length of pipe at the proper slope (1inch per ft sound alright?) and 1/2in holes drilled in the bottom side every 6in the last 4-5ft. At the end would be another 90deg elbow attached to a pop-up emitter. The trenches would be dug just large enough to fit the pipe below ground the first 5 feet, then widen it to 2ft wide 2ft deep the rest of the run. Line the trench with the proper fabric and fill with clean rock, put more fabric on top and cover with dirt and sod.

Thoughts? Does this sound alright? Will we have any issues later on? Will the water that runs off in the winter cause damage to the pipes because it's not below frost line? Any other solutions you can think of that won't require heavy equipment to be brought in?

I know pop-up emitters aren't preferred for this, but running a 300ft trench and tearing up the parking lot to daylight it isn't in the budget.

Thank you for your input!

[cavalierowner]

I'm no civil engineer (I'm an architect), but that would worry me a bit. That's a lot of roof area, thus a lot of water in a heavy storm. Are all 9 of the downspouts actual downspouts or are some of them emergency overflows set 2" above the roof surface in case downspouts plug up (required by code)? Have you researched raingardens? Our civil engineers have used them quite a bit in the last 5 to 10 years and they are actually quite attractive when landscaped properly.

[CAMAN]

They are all standard downspouts. The building is 40 years old so I'm sure code was different back then. Rain garden would be nice but like I said they want the cheapest solution and digging up the entire 200ft wall in the back of the building to put a garden nobody but the employees will ever see will not go over well with the owner.

[youngie22]

a cleaner look may be having your downspouts go straight into drain tile barried in the dirt and going all the way to lower ground or a spillway. or you could dig a big pit @ the end of the drain tile near the edge of the property and fill it with rock and sand for the water to drain into and disperse. no elbows, no pvc, should work in most cases!

[Tom7227]

I'm not a math wiz but there's not much chance of the idea working as I can see. A roof that size is going to dump 2500 square feet of water with a 1 inch rainfall. (sure my math can be wrong but the idea isn't) That's a lot of water and not that much rain. Where are you going to find soil that can take that much water in a reasonable period of time without causing problems like wet basements and such? Hate to use the reference but I recall a This Old House segment where they were working on a cistern system for a house roof and I'm pretty sure they had at least 2 in-ground tanks of at least 1500 gallons each that had lots of gravel under them, a large overflow channel just in case, and maybe even a system to work the water into the underground sprinklers to use it up.

About 2 days after this thing you're planning gets installed some city inspector is going to come and red tag the whole mess and probably laugh his [PoorWordUsage] off on the way back to the office.

[CAMAN]

There are no buildings with basements within a block of us. The ground is all sand and drainage isn't an issue. Right now after a large rain the ground is dry within an hour, never seen any puddles. I'm not worried about where the water will go once it gets to the end of the run, if there is too much water it will flow out the pop-up emitter and either soak into the ground there or flow to the street like it has been doing for the last 40 years with the gutter extensions, only thing different is the way it gets there and a little bit of drain tile to soak up the light rains.

Maybe I'm not describing this idea very well, I will try and sketch up a drawing and post it tonight.

[CAMAN]

Here is my idea...

[MuleShack]

You may run into the lower elbow freezing in the winter, which may mess up your popup.

Why dont you just run the drain pipe into a hole filled with rip rap. The rip rap would be heavy enough so that it wouldn't move with water flow and the water would disperse. This would eliminate any freezing in the winter.

[youngie22]

I see your idea better now! It would be nice if you could use the slope of your elevation and dump it into a holding pond or straight into the gutter of the city streets!

[Surface Tension]

I think your plan will work from April-Nov.

Come Spring when daytime temps rise and melt the snow off the roof your underground system will be frozen.

For that reason I'd remove the connection just above the ground in late Fall, replace with an elbow and downspout section above ground.

You said the owner wanted cheap.

[pureinsanity]

I just did my hours because of heavy rain falls it was washing away my dirt and grass.

I would only use the PVC if its someplace where trucks or cars would be driving over it. As a landscaper when we would run drainage systems under patios or under retaining walls we always used pvc where the load was and then switched back to drain tile.

Couple options here. you could run 4 inch corrugated drain tile right up to the gutter. They have gutter attachments that connect your tile and gutter together. Or you can install a tile catch basin at the bottom (which is better at keeping debris out of your drain tile) but is more expensive.

Get the tile that has holes precut into it with a sock over the top. It will allow water to drain after it is done flowing. This will help the freezing problem. I love the pop ups because of how you can hide them in a yard. The pop ups have a hole in the bottom of them to allow water to drain out after its doing doing what its made to do. Thus freezing should not be a problem.

The owner wants cheap, I would just go the tile route. Yes PVC is cheap, but the time you spend drilling holes you could already be started on your next area you are planning on tiling.

[LightningBG]

Couple options here. you could run 4 inch corrugated drain tile right up to the gutter. They have gutter attachments that connect your tile and gutter together. Or you can install a tile catch basin at the bottom (which is better at keeping debris out of your drain tile) but is more expensive.

[CAMAN]

I'm not a fan of the black corrugated pipe when it's near lawnmowers and trimmers, if it were protected like the picture above I probably would use it, but I'm going to stick with thin wall PVC. We also drive trucks on occasion and a large lawnmower on it so I'd rather it have some support in it.

Thanks for the input guys, we should be getting started in the next couple weeks.

[Dozer]

I really dont think you will be able to get that water to soak away fast enough. That is alot of water you are talking about. If you really dont want to use any heavy equipement you arent going to get your rock filled sumps deep and large enough to have the capacity to hold enough water so that it can soak away slow enough.

[pureinsanity]

I'm not a fan of the black corrugated pipe when it's near lawnmowers and trimmers, if it were protected like the picture above I probably would use it, but I'm going to stick with thin wall PVC. We also drive trucks on occasion and a large lawnmower on it so I'd rather it have some support in it.

Thanks for the input guys, we should be getting started in the next couple weeks.

Since you don't like the look of tile going into a gutter and PVC will look the SAME. Then use these catch basins instead.

Gutter drains into them, they are buried level with the ground then attach your drain tile or pvc to them.

[CAMAN]

Since you don't like the look of tile going into a gutter and PVC will look the SAME.

Oh, I don't care about the look, it's the durability of the thin black plastic. If it gets brushed by the mower or zipped by a trimmer it will easily get damaged. And I'm not very worried about debris clogging up the tile, there are no trees within 100 feet of the building and it's tall enough that the only foreign object that ever gets up there is a little bird p00.

[pureinsanity]

best of luck to you and your project