Thinking about wastewater could save you thousands.

Building an ADU? Here’s what you need to know about planning your sewer line.

If you’re converting your garage or building an accessory dwelling on your property, you’ll need to consider every aspect of plumbing when planning your budget. That includes the plumbing that’s buried in the yard. If your ADU is detached from the main home, you’ll need a new line to remove wastewater. If it’s attached, you can tie it into the existing sewer line although that may need to be repaired, replaced, or upgraded to accommodate the additional usage.

What happens to wastewater?

Wastewater comes from our sinks, toilets, showers, bathtubs, and appliances. It’s one of those things we deal with every single day, but we don’t often think about where it goes once it’s out of sight. It’s also something that isn’t the fun part of designing a project but an essential element to consider during the design process. The wastewater drains from your home into your main sewer line. In most cases, that line carries the wastewater to the city connection at the street. From there, the wastewater travels to your city’s treatment facility.

Gravity keeps things moving.

Usually, the pipes in your home and your main wastewater line use gravity to carry wastewater to the city’s line, which takes it to your city’s treatment facility. The line has to gradually slope downward for this to work. To be exact, it has to have ¼ inch of drop per foot. Otherwise, the water won’t flow properly. In some situations, where a new project is built downhill from the street and the main sewer line, a pump is required to get wastewater to where it has to go.

Calculations are critical.

It’s always smart to measure everything before you build. You’ll need to know where your city connections are as well as where your wastewater line will go and how deep it will be. Typically the General Contractor and their plumbing subcontractors handle the technical aspects of the wastewater sustem. Russell Feirstein, a New Avenue client who recently oversaw a wastewater line repair and ADU construction on his own property, describes the measurement process well:

From your [ADU site], walk the line through your yard, using the most accessible parts of the yard that will no doubt be dug up for the line. Note the number of bends it might take and get a complete measurement to the street connect. The required slope depth is 1/4 inch per foot of drop for proper water flow. So, you would take that total footage from your garage to the street hookup in feet and multiply that by 1/4, then divide by 12 to get the droppage in feet. That will give you the depth of the new line that will be going from the garage to the street/sidewalk hookup. That depth is important to know. If the measured depth of the street hookup is 5 feet down, and your calculated distance is, let’s say, 180 ft / 4 =  45 / 12 = 3.75 feet down, then you are GOOD as the street pipe is LOWER than your line’s needs. It would just have an angled drop before the connect to have it drop the extra foot or so.

What if there’s not enough room to get the right slope?

If you do the above calculations and discover you don’t have enough space to get the proper slope, you’ll need to install a pump to force the water toward the city connection. That can be costly, but since you’re planning ahead, you can budget for it.

Let us handle the dirty work.

Trust us—sewer-line surprises are most unpleasant. But don’t worry; when you work with New Avenue, you have the top ADU experts on your side. Your New Avenue design professional will optimize everything about your ADU, from the placement of your sewer line to environmental efficiency to the welcoming façade that will greet your guests.