Rain drainage options for flat roof patio??


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Old 05-28-24, 07:48 AM
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Question Rain drainage options for flat roof patio??

I have a semi enclosed patio (approx 225 sq ft,14.25' x 15.8'). The problem is it has a flat roof and no gutters, and when it rains, most of the water pools to one side and falls over the edge. This has led to erosion over time (we've been at the house almost 2 years). (Please ignore the deck box in the photos, it's down on the grass because we just refinished the patio concrete).

I've recently done some work on the patio and am looking to do some more. As part of this, I'd like to install some kind of gutter system. My thought is to use pieces of roof drip edge (along with black silicone to water seal the edges and around the washers and screws) and direct them all to the edge where the water is naturally collecting. Then install a rain chain down.

But then I'm a bit stumped. I have thought of two options I have thought of, and could use opinions. I could either:
1) Have the rain chain dump into a catch basin that I dig out and back fill with river rock. I'm thinking a 3x3 ft roundish area, 2-3 feet deep. And I would drill some very small holes in the edges so that it would slowly drain into the soil around it. (I really don't want to go through the hassle and expense of building a french drain system -- but please let me know opinions if this is necessary -- to get it out to the sewer, it would be approx 200 feet).

2) I could dig a 3-4 foot strip from the patio and concrete pads ending (see the last picture). And fill that with river rock. That area is kind of a pain to keep mowed anyway and the cinder blocks that are there and border the cement pad are not even.

Anyway, open to any and all advice and suggestions please! I'm including a bunch of pictures of the space. The first one is the view of the patio door from inside the house. The next is the upper right hand corner of the patio, which is the corner where the rain collects and falls when it rains. The third is an outside view of that same corner and where I could dig out and put river rock along the edge of the cement/concrete pads if I did option 2. The fourth is a view of the land where the rain falls and where I could put a rain basin under option 1. The fifth is a view of the patio roof from the upstairs window.

Inside view from the patio door.


The corner where most of the rain falls from.


Where I could dig out and put river rock potentially if I did option 2?


Where the rain drips down from that corner. And where I could put the rain chain and basin.


The top of the patio roof (view from a window upstairs).
 

Last edited by PJmax; 05-28-24 at 09:58 AM. Reason: pics hosted/posted PJmax
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Old 05-28-24, 07:50 AM
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For some reason the pictures are not showing up in the post. Darn it, so I'm uploading them in a doc file and seeing if that works.

 
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pic.doc (3.86 MB, 8 views)
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Old 05-28-24, 08:13 AM
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There is a problem with the website displaying images. A few moderators can see your photos but most people cannot. The techs are working on the problem.

Both of your options collect the water right next to your patio & porch and expect the water soak in. That could lead to foundation problems and with moderate rain I would expect those collection basins to overflow. Instead I would try to drain the water away from your home.
 
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Old 05-28-24, 09:58 AM
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Posted pics to board.
 
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Old 05-28-24, 09:58 AM
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Not trying to sound dumb here, but the patio edge is 14+ feet from the foundation of the home? So are you saying it could cause patio foundation issues? It's been here for over 15 years, so wouldn't this have been an issue the whole time?
 
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Old 05-28-24, 11:14 AM
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Your patio and screened porch are also permenant structures with footings. Any water next to the building should be avoided. Digging large holes right next to the building like you suggested isn't the best idea. You can collect the water and run it in pipes to French drains located further away from the home. You can even include an overflow so when the French drain is waterlogged the water can dump harmlessly on the ground well away from the home.
 
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Old 05-28-24, 12:20 PM
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Gotcha. So, a few questions on that. 1) how deep would I dig to run the pipes. 2) how big of pipes should they be (and are you thinking/talking like PVC? 3) how far away would you run it before I'm "safe"?

Appreciate the advice!
 
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Old 05-30-24, 03:42 PM
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If you build a brick pad where the water falls from the patio roof, will the water flow away from the house over the lawn all by itself?

You may need to create a swale (wide and shallow ditch the blends into the lawn) to get rid of the water.
 
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Old 05-31-24, 03:06 AM
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4" is the most commonly used size for drainage. I prefer thin wall, smooth PVC but corrugated black poly pipe is cheaper.

The pipe's depth is not important. Some people even leave them on the surface. So, bury it as deep as you want but you have to take your properties topography into account. You need somewhere downhill to run the pipe. The deeper you bury it generally means you have to run it further away. I don't like to discharge water any closer than 10' from the house provided the water will run away from the house.
 
 

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