Sizing Water and Sewer Laterals?
Within new developments, the water and sewer lines are placed in trenches underneath the new streets to be constructed. To avoid asphalt repair and additional costs after the streets are completed, the pipeline contractor will typically install “laterals” from the main lines to at least behind the curb. The builder will later extend these laterals to the home or building, providing the water and sewer service from these main lines in the street.
The water and sewer main lines in the street tend to be 8 – 10” in size, made from a PVC plastic material. The laterals for single family homes, also made of PVC, tend to be smaller – sewer laterals of maybe 4” in size while water laterals are typically ¾ – 1”. The civil engineer will designate these lateral sizes on the site improvement plans, usually based on experience and/or city requirements. Generally, the water meter sizes for detached single family homes will be 1” to accommodate the domestic needs as well as newly required fire suppression sprinklers within the homes. Some cities will allow meter fees based on ¾” size, yet a 1” meter will be installed if you can obtain a letter from the Fire Marshall.
One comment that I have heard from civil engineers is how these laterals are sized for multifamily buildings. The civil engineer needs to defer to the building MEP (mechanical/electrical/plumbing) consultants for sizing these laterals because the water pressure and sewer capacity for a multi-unit building is dependent on the number of water supply fixture units (WSFU), building unit count, and available pressure from the supply main. For multifamily buildings, the sewer laterals can range from 4” – 8” in size and water laterals from 2” – 4”. Not being the building expert, the civil engineer cannot make this call.
As always, we welcome your comments and questions below.