VDC Underground Process

Steps for Underground Drainage Routing 

• Locate sewer entrance from civil site plans 

• Plan on the elevation of the sewer coming into the building either sitting on top of the footer, or under the footer  

  • It's easier for the plumbers to place a sleeve sitting on the footer rather than have it higher in the foundation wall.  

• When routing the main sewer line, it's okay to use more pipe to follow the over dig of the frost walls. 

  • The over dig is on the downhill side of the house, when the civil guys dig to pour the footers and foundation wall they don’t back fill that portion of the house. That is the over dig we want to follow 

  • From inside of the foundation wall to center of the pipe we want to be 18"-24" off of the wall. 

• When branching off the main sewer line, keep the branch lines as high as possible 

  • This will avoid digging long deep trenches 

  • The hub of the farthest fitting that is setting your elevation can be into the slab if you need the elevation.  

Routing Hierarchy 

Easier Install -> Save Fittings -> Save Pipe 

Example of a Typical Foundation Wall Detail 

Things to look for before sending under grounds to prefab: 

• Your pipe lengths are optimized to 20’ sticks. 

  • If you optimize a 42’ straight length, we want the two 20’ sticks to be further down stream then the remainder 2’ up stream. 

• Run your main line in the over dig if you can, even if its more fittings. 

  • We want to be 18-24” off of the inside foundation wall. 

  • Running in the over dig helps us avoid digging trenches. 

• Bring your sewer entrance in on top of the footer, you can always offset up. 

• Keep branches as high as possible, we don’t want to be digging unnecessary trenches.  

  • Offset up off the main line even if you are rolling up 22.5 with a street 22.5. 

  • Only come off the main flat if the street 22.5 is too high of an offset. 

• Look at your furthest fixtures to start your elevations. 

  • The furthest fitting can have the hub in the slab. 

• All pipes coming through the slab should be 1’ above slab with a cap. 

  • The exception is floor drains or floor sinks that get poured in the concrete. 

  • Showers and tubs get blockouts. 

  • Do not add couplings above the slab as part of the prefab, that is only going floor to floor in a framed house not through the slab. 

• Swing fittings when you can to eliminate extra fittings. This applies everywhere not just in undergrounds. 

  • For example, rotate a vertical san tee 45 degrees and add a street 45 or a piece of pipe then another 45, this is two fittings. Rather than having the san tee straight with a street 45 for the offset and another 45, this is three fittings. 

• There is nothing wrong with bringing up extra risers if you aren’t sure if one’s going to work. 

  • If you bring up a riser and we don’t need it, we will just cap it. 

  • Also look to see if there are unnecessary risers.  

• If you have to be low because of an interior footing, offset up after to keep everything high. 

• Keep cleanouts in mind, all branches over 5’, every 50’ and at the end of the line need cleanouts. 

  • If you turn more than 135 degrees, you technically need a cleanout.  

• Try to avoid running long distances under walls, I wouldn’t go more than a couple feet. 

• Keep the piping as square to the building as you can.  

  • Running at long 45 angles or odd angles makes it harder to install and if the pipe ever needs to be dug up being square is easier. 

• Utilize the swing of the P-trap 

  • You don’t have to hit a p-trap head on, that can swing at any angle. 

• Don’t run two pipes parallel over the top of each other, this is hard to support the pipes. 

• When the building has an angle change that isn’t 45 or 90. You can have two 90s to make a swing joint, this is typically a 90 and street 90. 

• Ideally, we will have a deep underground installed before the interior footers. 

  • This helps us avoid tunneling under footings.