If they intend o\to put a glass ceiling on the courtyard, they will plant things or put in a fountain. there will be less water. but you have to design for phase 1. Check the rainfall data back at least 5 years and then add 25% for climate changes. They may never put up Phase 2 and roof.

There will be no glass ceiling, it will be come a courtyard enclosed on all four sides, which increases the importance of assured drainage.

i could boil down the question to,,, how do you design storm drainage under a building. my firm doesn't like the liability. I'd like to get more experienced on it.
I understand that pipes under foundations need to meet IBC. I will research it. Where does MEP design scope begin and a civil site design scope end when it comes to situations like this? we usually say that our design ends 5' from the foundation,,, what if that foundation is delayed 10-20 years and may never get constructed.

thanks

How pervious is the soil? If it's sand or gravel, and you direct the roof runoff to the outside, you may be able to get by with rain gardens or drywells in the courtyard.

I'd belt-and-suspenders the pipe. Even though the Q will probably be low, you wouldn't want a leak under your foundation. Maybe put it inside a sleeve, so it could be replaced without busting up the floor.

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. - http://xkcd.com/319/

sub-surface retention using either HDPE or CMP pipes.
perforated with sand or gravel bedding to allow infiltration below
overflow gravity drain to allow drainage if it fills
design for clogged inlet
provide some way to maintain and remove any sediment or debris (manhole?)

use 100-year rainfall, not 5-year and add a large safety factor.

I would run a properly sized RCP pipe underneath the level of the proposed foundations with a manhole/inlet at each end just outside the building. Coordinate with the structural engineer for a stepped footing or run your pipe through the footing (probably stem wall above footing).

ACtrafficengr & cvg, the IPC says to use 100 year 1 hour storm event so yes, i'll over design it for sure. jgailla, the pipe will be constructed and then some time in the future will be covered by the building so we can't go through the footing unfortunately. Sleeve encasement is a decent option, i'll have to explore that a little more.

im leaning towards class IV RCP, water tight with manhole on either side of the future building expansion footprint. type 1 bedding.

Quote:

How pervious is the soil? If it's sand or gravel, and you direct the roof runoff to the outside, you may be able to get by with rain gardens or drywells in the courtyard.

I would recommend against this if at all possible. If a dry well overflows on a site, it's no big deal. If it overflows in a courtyard, it's a very big deal. There's also the issue of wet feet for your foundation. Infiltration measures usually have a setback from foundations for safety reasons.

To answer the overall question, it really depends on the municipality what they'll let you get away with. My home has a fully enclosed courtyard, and it drains fine with a 3" PVC pipe that's buried under my foundation slab. I wouldn't specify that on a project I was designing though. If I could get the design to show that an 8" or lower pipe can handle the flow, I'd do it with DIP, personally. RCP isn't a bad option, as long as its water tight, but if it's under a load bearing foundation you'll need your structural / geotech folks to weigh in. Under any differential settlement the bells in the RCP could shift and allow infiltration/exfiltration. You definitely don't want a sinkhole under your building. In Atlanta, I have seen this sort of thing done with an RCP pipe encased in concrete. I've also had structural designers design "cut outs" into cast in place load bearing concrete walls, where they make a kind of a rebar diamond around a hole for my pipes to go through.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

beej67, good point, especially since severe rainfall events are becoming more common.

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. - http://xkcd.com/319/

You asked about MEP because you go under a building. You won't connect to the building, so no MEP. You don't want them involved anyway.

The point of entry into the courtyard for yard equipment should be where the storm drain line is to be buried as there should no foundation to penetrate.