Fdn. Drains Connect to Roof Drains

[zennis]

What are some opinions regarding foundation and underslab (slab on grade) drainage systems that connect to roof drains that connect into the storm water system. Are there concerns of backflow. What if the existing storm line pipe is below the foundation/underslab drains?

Thanks

 

[ACtrafficengr]

If you have deciduous trees nearby, don't do it. Blockage by fallen leaves getting into your drainage system is a real concern. If you must, perhaps you could oversize the pipes to reduce blockage, or provide plenty of cleanouts.

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

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[GeoPaveTraffic]

As a general rule, I don't recommend it. The potential for problems is too great. However, if you really need to for various reasons, make sure that the main drain line is several feet below the floor/wall drainage system and oversizing the line as ACtrafficengr recommended is a good idea.

 

[emmgjld]

I have done this many times. I have also not done it many more times. One of the usual problems I see is the roof piping tends to be undersized, sometimes greatly undersized. I typically use one conduit for roof runoff and a separate conduit for foundation/slab drains.

 

[runoff]

I have done this several times and has worked out okay. The only problem that I could see is the possibility of trees or large shrubs that have root systems that could penetrate the drainage system. However, most of the time it works just fine. Just make sure you size the conduits accordingly.

 

[TDAA]

If you have expansive soils, you open the possibility of additional wetting. That would be bad.

 

[zennis]

Thank you for responses. The concern was if the main storm sewers backup and resulted a back pressure this would exert a force (or possible hydrostatic force) on the foundation wall or slab on grade that could result in structural issues.

If we use a check valve on the foundation drain this would mitigate hydrostatic forces due to backflow water.

 

[TDAA]

Put in a sump, that would handle overflow. Pipe it so the invert into the sum is higher than the pipes of the poundation drain.

 

[MotorCity]

Check with your local municipality, many prohibit doing this because it adds unnessecary demand on the sewers and treatment process.