[iivel]

So, the issue started that the grade of the house landscape was towards the house. There was an old slab w/ a massive void underneath which was causing moisture problems in the basement. I didn't have the ability to regrade the entire property, so opted to correct the area affected in the back. I had the area graded out 21' from the house and 47' wide. (picture 1).

To keep erosion from being an issue, I trenched out and installed a retaining wall. To maintain grade away from the house, and to bring the level down correctly below my siding this makes it approx 8" below grade (picture 2). So now the problem is water pooling within the retaining wall like a big pool (picture 3 &4).

So, how would you go about correcting this? I compacted in a 2" sand bed over the 4" of fill gravel and was starting to lay pavers when we got our first solid rain. Now I think I have more work to do. My 'current' plan is a french drain behind the retaining wall about a foot and run drain lines into the french drain on both patio corners and a couple spots in the center. I'd run this drain to where it will drain into the street sewer system. Does this make sense?

Any help is greatly appreciated!

Thanks.

[Stonehenge]

I would say to make sure that you get the approval of your municipality before you tap into the sewer system (probably not a big deal, they just want to make sure you're doing it the right way), but instead of a french drain, just pitch the patio to a drain to collect all the water and route that water to that sewer system, or somewhere there is a lower elevation.

[agla]

I think Stonehenge meant to say drainage system rather than sewer system.

You seem to have what is known as a "sheet wash" grade which is a slope in one direction with no cross slope. The good thing is that your patio edge will be even across the retaining wall. The difficulty is that the water lands evenly along the wall and will need a trench drain to effectively pick it up instead of one catch basin if it drained to a corner.

You can buy trench catch basins, but you have 47', so it would add up. A more economic and still effective (if you do it right) method is to finish the patio short of the wall and build your own drainage by digging a trench with a rigid perforated pipe pitching from one side to the other in a trench filled with large round clean stone. The low end of the pipe should be connected to solid pipe pitching down hill to daylight, a drywell, or an existing drainage system.

The pitfalls are that you most likely have stone under the patio that may fill with water faster than the drain pipe if you don't set that pipe lower than the subgrade under your patio base. That means starting deep and then pitching deeper. The gravel trench has to be open to the surface and wide enough to take in that water.

[MLysiak]

I would also address that gutter downspout to exit somewere that it doesn't add to your problem. (pic 1, Does that dog hunt?)
M-

[iivel]

I'm planning on bringing the gutter downspout a bit higher (it's nearly below grade) and running a long 6" ID flexible pipe out to the yard approx 12 feet on the side of the house.

Thanks for the input on drainage. What type of grade should I do for the gravel trench/pipework next to the retaining wall? I'm assuming that I should not pave over it?

[agla]

1" per 4' and you would have the drain rock exposed to the surface to let water and air in.