I need some help with a draining problem at my house, if you all don't mind.

I've got a house with a completely enclosed atrium in the center that is open to the sky.  Part of the roof drains towards the atrium, which is surrounded by gutters.  Those gutters feed into a 4" PVC drain system, which also has 3 surface drains in the atrium.  There is only a single line for the drain to exit the atrium, and it does so under the slab of the foundation.  The drain goes under a deck, downhill about 10 feet, and into the city's buried storm drain.  It is not covered by concrete where it is under the deck and the steps.





I've lived in the house for 6 years.  There appears to be enough capacity to drain the atrium and that portion of the roof.  However, during long, heavy rains, the drain suddenly stops working.  Water starts to accumulate in the atrium.  It has gotten as deep as 6 inches before during hurricane remnants that pass over, and within an inch or two of the door sills.  This obviously worries me.  When the rain lets up, the drain will suddenly start working again and the entire atrium will empty in about 5 minutes.  

I suspect that when the water gets high enough in the city storm drain, it blocks or severely decreases the flow from the house drain.  Water backs up until the level drops in the storm drain, then it can empty out.  

I do not think there is a clog, given the way the water suddenly stops flowing, then starts again.  There's something else keeping it from flowing out at certain points.

I do not believe it is feasible to install another drain under the foundation.

My proposed solution is to install a Y-joint at Point A (where the drain passes under the stairs for the deck).  Water could flow normally into the storm sewer, but would have an alternate way to flow out.  That would just drain onto the driveway (live every other house in the neighborhood does), then flow across the pavement into a storm sewer opening.

Thoughts?  I've got a drainage company coming out in a few days, but I wanted some ideas.

Thanks!

Your idea sounds like the right fix.

I'm surprised the builder was allowed to connect directly to the storm drain system in the first place.

Sounds like a great opportunity to build a nice cistern in the atrium.

That's what I thought also.  It was built in about 1981.

I thought about that.  Not sure if it's in the budget, though.

Storm systems are designed using "Hydraulic Grade Line." This basically determines what size pipe is required for x amount of water to pass through at y amount of speed. Sounds like either your system or the city system is not good enough for a 10 year storm event. In other words, bigger pipes at a sufficient grade are needed.



ETA Or you could build an awesome roman style pool.

After reading your idea, that sounds like a reasonable place to start. It very well may solve the problem. If your drain is just to small at the house though, it may not. I think you've chosen the best initial attempt at a fix.

Sounds like your "y" is a good solution. Are you sure there aren't any obstructions in the current drain pipe? Roots, debre, etc...? Have seen similar situations where the water was only a problem once or twice a year, and an added sump pump or lift station was added as a "back up" when the water rose to high.

I don't think there are any obstructions in the drain, given how it flows fine until a certain point.  Then, a complete stop.  Rain lets up for a bit, and it suddenly starts flowing again.  Happens every time there's a heavy rain.  That's what makes me think there's something else besides a clog.

Not knowledgable enough to have an opinion re: the drainage but that atrium setup intrigues me.

It's the main reason we bought the house.  It's got floor-to-ceiling windows all the way around it, with 3 sliding glass doors.  There was a wooden deck in it originally, but we had that removed and put in a stone patio with a fountain and landscaping.

I'll see if I can find some pictures when I get home.

Your drain idea sounds about right.

I'm surprised to begin with though, that this drain actually goes into the storm sewer directly. It's just residential rainwater...right? I HOPE!

Honestly, if that drain is ONLY for storm drainage, I would block it off and run ALL of it out onto your driveway.