[Bill Schwab]

Code in San Diego city require a connection to daylight every 50'. So, if you have a wall 70' long, there should either be two T's connected to your sub surface rain water drains heading to the street, or, you can core cut a hole through the wall face and set them flush with the wall right above grade.

There are 3 different types of white rigid pipe in our neck of the woods....Triple wall, which is kind of corrugated on top, then there is Michael Jackson pipe, (black on the inside white on the outside) hey don't laugh, that's what the pipe suppliers call it, and SDR-35. All we ever use is SDR-35 because it is a gluable pipe, and you won't get any root penetration through the connections as you will with the triple wall or Michael Jackson varieties. Christies makes glues and tapes for the lessor qualities of pipe, but typically they will crack and fade after a year or so underground and you have the same root problem as no glue or tape at all. Using black flexible pipe will work but there are two problems. First, it can collapse from the weight of the rock over the top of it. Second, because it is flexible, it can droop in spots, creating a snaky type look and causing water to head for the low roads. Also, this black pipe has to be adapted to any of the white pipes you would most likely have for your sub drains. You usually use pipe tapes for that, but once again you will face the root penetration issues.

The pipe behind the wall in the 3/4 drainage gravel should have a 1% pitch on it, and for runs over 50', we typically will set the middle high, and connect drains at each end. We don't wrap the pipe with a sock. We wrap the gravel drainage rock entirely with geo textile fabric. The reason for that is, a sock on a 4" pipe can clog much easier than a great big wrap over the entire run of gravel.

With respect to holes up down or sideways in the perf pipe. One set of holes has to go down, the other face the back of the cut into the gravel. At least that is what the inspectors called us on at the least wall we had going up. So, we had to make the adjustment. The method to the madness is this. San Diego has 5 basic soil types. If you have the sandy loam found in most of the beach communities (Solana Beach, Del Mar, Encinitas, Carlsbad, etc, usually lying within 2 miles of the ocean, the holes are not as critical. But, if you have Class 4 expansible, silty clays, or even some DG's, the reason they want those hole facing down is for ground perculation. If the holes are down they grab water and "distribute" it as Penn has eluded to. If they are up, and you trap water behind the wall, the water will work the sub soils until it fails causing your wall to blow.

There is yet another trick to the mix here. If you have sub drains, those drains have to be underneath the the bottom of the wall footing in order to make a connection below grade, otherwise the footing itself will trap the water and it will have no where to go.

If you can't make the elevations work to connect below ground, that's when you compact base behind the wall, at the same elevation as the ground on the daylight side of the wall. Then lay the pipe, and core drill at ground level through the wall face and dump your water at the toe of the wall. Install some area drains to get it out and stop puddling in front.

Because of the variable soils we have in the region, every precaution is thrown at us when we install a wall. To many, all this seems way overkill. But it is what it is.

I hope this helps.