Zero lot line homes are similar to duplexes. They're two dwellings under one roof with a common wall between the residences. However, duplexes are usually rental units. Zero lot line homes are sold to owners and are compared to condominiums.
At the Villas of Chapel Hill, the homes have an innovative wastewater disposal system called STEP, septic tank effluent pump, that foreshadows increased growth here. This different kind of utility for indoor plumbing is being used more frequently in nearby counties where they're far from city sewage treatment plants. That encourages growth because the developments are not tied to a sewer leading to a municipality's treatment plant. Homes and stores can be built almost anywhere water service is available. Furthermore, owners won't face all the requirements of a traditional septic tank.
The systems are a "tremendous benefit" to developers, says Eddie Walls, Warner-Brothers Development building superintendent at the Villas.
STEP systems are not new. They've been used for decades at interstate highway rest stations. Rural schools use the sand filtration process that's an important part of STEP systems. State regulations over such systems for subdivisions have been enacted in recent years because of STEP systems in Williamson County. They're in Bedford, Rutherford and Wilson counties. Here, one was built for Chapelwood years ago.
"STEP systems are like portable infrastructure," County Building Official Don Nelson says. "If that (proposed amusement) park is ever built (on the Maury County line) it would probably use a STEP system. Who would run a sewer there?"
County officials and leaders of the Villas of Chapel Hill recently explained the zero lot line homes and their STEP system at the development. Four of the planned 74 residences are available for occupancy at about $150,000 each. They're on the west side of U.S. 31-A (Horton Highway.) And being built by Warner-Brothers Developers.
The Villas are the "first zero lot line home subdivision developed in Marshall County," according to County Commissioner Mary Ann Neill whose professional work as an appraiser takes her to many home-sites. "These are exceptionally popular in Spring Hill and Maury County."
They're also a prominent part of a residential area south of Black Fox Elementary School in Murfreesboro where zero lot line home development offered economical construction because of the common wall between two dwellings under one roof.
The Villas' 37 buildings are on 29 acres, Walls said. Most of the homes will have three bedrooms and two bathrooms in 1,562 square feet of living space. Each unit is to have a two-car garage. There will be some two-bedroom units in the same square footage. Construction permits for the homes and STEP system were obtained in February. Work on the first house started in March.
Neill who also is a county planning commissioner said a homeowners' association is to be formed to take care of subdivision yards and other landscaping. "It's excellent for young singles and retirees who don't want to monitor their yards," Neill said.
Nelson has coordinated discussions among Marshall and Bedford counties' planning and zoning board members so they may learn about a trend in land development. Sometimes it's called neo-traditional development. Sometimes it's called smart growth. Frequently, it means efficient use of land and homes that are close together. In such developments there may be open space for a neighborhood playground instead of large back yards.
Coupling zero lot line homes with a STEP system was seen by Tommy Whaley of the county water system as a remarkable step in county development, so he coordinated a gathering of the Villas' leaders with some county officials so both groups could mark the occasion of this step in county development.
"This is a reflection of the foresightedness by the Marshall County Planning Commission and the Marshall County Commission," Nelson said. "If this was a conventional development with septic tanks, and if there was a failure, we'd never know about it. But this is monitored by the Tennessee Department of Environment and Conservation (TDEC) so we're all behind it."
Bob Ramsey is an engineer with James C. Hailey & Co. in Nashville, the firm hired by Warner-Brothers for the Villas. The Villas has a "recirculating sand filtration, wastewater treatment plant," Ramsey said.
"At each house we have a water-tight septic tank," he said. "Each tank has a pump to send the effluent from the tank to the sand filter."
Wastewater from the tanks is pumped through the neighborhood's sewers to the sand filter field where it's filtered five times, he said. After a fifth cycle, the effluent is collected and it's sent into a treatment building, through more filters and a pair of ultraviolet disinfection tubes.
From there, effluent is pumped to a drip field where half-inch pipes are buried about seven inches deep and five feet apart, Ramsey said. Every two feet there is a hole in the pipe and a small plastic device, an emitter, at the hole in the pipe. The "emitters allow .61 gallons of water out of the field line pipes' holes every hour," Ramsey said.
The field lines are deep enough to allow some use of the land above, but shallow enough so that the water can be taken up by the root system of whatever vegetation is planted on the 3.8- acre field, Ramsey said. The sand filtration area is 90-feet long and 55-feet wide. It's covered by crushed rock.
The closest home to the disinfection building is about 200 feet away, or about 75 feet from the property lines of those lots.
The Villas are north of Chapel Hill and south of Holt's Corner. The Marshall County Board of Public Utilities stands as the governmental agency to monitor the system on behalf of TDEC which, ultimately, has control.
STEP systems are what the county building officials had "always felt" would be used if an office building were built on its own campus in the county, Nelson said.
"Previously, we were told STEP systems needed about 60 lots [home-sites] to be financially feasible," Nelson said. "Tommy Whaley and I went to Wilson County where they're used and were told individual businesses have their own STEP systems."
"I don't know that the theme park would use a STEP system," Nelson said, "but it's an option."