How deep should a house's sewer line be buried?

Answered by Brett ~ March 19, 2012 ~ No Comments

The old sewer line from my house to the curb has collapsed and I want to replace it with new PVC. Because the pipe exits from my house only 6 inches below the ground surface, I am worried about it freezing in the winter. Is this sewer line to shallow? Any suggestions?

Forrest ~ Colonial Heights, VA

Brett Kulina

Forrest, although your home's existing sewer line might be susceptible to freezing due to the shallow depth at which it is now buried, an equally important factor to consider is the slope at which the pipe angles down towards the curbside sewer main. Most properties don't have pump-driven sewer and waste systems, which means that gravity is solely responsible for keeping the pipes clean and your home's sewer waste moving in the right direction. If the angle of a sewer pipe is too steep, debris can cause obstructions, because the liquid waste tends to then separate from the solid waste. Likewise similar problems can occur if the angle of the pipe is too flat, because none of the waste is moving fast enough.

If your home's existing sewer system was working without issue prior to the collapse of the old pipe, then perhaps installing the new PVC pipe in the same configuration would be an okay way to go. A better option could be for you to consult your local building and sewer department when you are getting the required permits, because they can probably tell you the exact depth at which their sewer main is buried in front of your house. If by chance their sewer main is buried deep enough, then you might be able to move your home's waste pipe(where it exits the foundation) deeper in the ground while still maintaining the correct drop in grade from your house to the curb.

If you do not have the option of lowering the pipe deeper in the ground, then you will have to insulate the area around the pipe as best you can. Depending on the average frost depth in the Colonial Heights area, encapsulating the entire pipe with foam insulation for a few feet could be more than enough protection to keep the pipe from freezing. Of course, many sewer pipes avoid freezing altogether, because the constant flow of waste water within the system helps keep the overall temperature above the freezing point. Before starting your project, you should probably get some advice from the local contractor who is digging the trench for your new sewer line and ask about the best way to insulate and protect underground sewer lines in your area. Good luck!

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