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County may revisit limits for building on slopes

Eileen JoyceCounty supervisors are reviewing a 1970 land use rule that limits construction on slopes steeper than 30 percent. Many of Alta Sierra's lots like this one were created in 1964.
ALL | GrassValleyArchive

If you walk 100 feet in a straight line, and the ground rises 45 feet, you will have marked off a 45-percent slope. Scott Biggs can do that on his Washington Road property near Highway 20.

There’s no house on the 35-acre property, and no immediate plans exist after his hopes of building on a 45-percent slope – with a view overlooking the South Yuba River valley – were rejected.

“The value of the property is in the view – not the land,” Biggs recently told the Nevada County Board of Supervisors.



Most supervisors sympathized, but they voted down the couple’s appeal because county policy in most cases prohibits home construction on slopes steeper than 30 percent.

It’s outlined in the county’s General Plan, but the plan is under its five-year review, and supervisors are awaiting a Planning Department study before considering possible changes.




“You’re exactly the reason this needs to be looked at again,” Board Chairwoman Sue Horne told Biggs.

Supervisor Drew Bedwell has been more adamant, characterizing the slope requirement as government intrusion.

But while some consider the slope requirement too restrictive, planners say it’s based in reason. While some say it limits soil erosion and septic problems while preserving aesthetics and firefighters’ access, others say building just about anywhere is possible with good engineering.

Is 30 percent a magic number?

It might have been reached by “political means,” said Andy Cassano of Nevada City Engineering.

“But,” he added, “technically it’s kind of a breaking point between simplicity and complexity.”

The county’s 30-percent slope requirement dates back to 1970, according to county Planning Director Mark Tomich, whose staff is researching the issue for the board.

This came six years after the opening of Alta Sierra, the community south of Grass Valley, where steep, vacant lots remain but are still buildable if construction requirements are followed.

From 1977 to 1981, the county’s slope requirement was tightened to 20 percent before returning to 30 percent in 1982.

The restriction has exceptions.

On existing lots that are entirely too steep, the county will sometimes allow grading – or flattening – of the land. A management plan and erosion report are required, and building requirements must be met, Tomich said.

Slope requirements also come into play when land owners want to build on a steep section of their property but have buildable land in another section. In the Biggs’ case, according to Tomich, the couple can build on other parts of their 35 acres.

The key factor in building on slopes is finding the rock that lies beneath the soil. Some rock is near the surface while some foundations are set 20 to 40 feet deep.

“Anything can be engineered. It’s just a matter of how much money people want to spend,” said Tom Holdredge of Holdredge and Kull Consulting Engineers and Geologists in Nevada City.

“Obviously from an engineering standpoint we can build on steeper slopes, but it gets more complicated,” Cassano said, adding that septic systems on steep slopes need specialized designs.

Slope rules aren’t specific to Nevada County, where the foothills are undergoing rapid development.

In El Dorado County, which is seeing similar growth rates, rules are more flexible.

Slopes 40 percent or steeper “shall be discouraged,” Principal Planner Peter Maurer said, reciting the county’s general plan.

“There really is no hard and fast rule,” he said, but the General Plan is being revised and so might the slope policy.

In Truckee, development on slopes greater than 30 percent is prohibited, except for single-family homes on existing lots. Development is also discouraged between 20 and 30 percent, Truckee Town Planner Duane Hall said.

The idea, he said, is to avoid erosion and ground disturbance, and also “aesthetic issues” because houses built into hillsides are often taller than most homes.

The challenges of building on steep slopes can be seen in Truckee’s 6,000-lot hillside subdivision that started in the 1960s.

About 800 vacant lots still remain, Hall said. “All the easy lots to build on have already been built on.”


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