Building on a Mountain Slope: What You Need to Know About Steep-Slope Regulations in WNC
There’s a reason people love building in Western North Carolina. The views are incredible, the land is beautiful, and a home tucked into a mountainside can feel like it belongs there in a way that a flat-lot house simply can’t.
But building on a mountain is very different than building on a flat piece of land. And in WNC, the slope itself can have a major impact on what and how you can build.
Steep-slope regulations are designed to protect the land, manage stormwater and erosion, and reduce the risk of slope instability. After what the Asheville area experienced during Hurricane Helene, we have an even greater appreciation for just how important those considerations are. They can also affect the size and placement of your home, driveway, septic system, grading, retaining walls and other improvements.
The rules vary depending on where your property is located, so there isn’t one blanket “WNC steep-slope regulation.” The City of Asheville, Buncombe County and surrounding municipalities each have their own requirements, along with state regulations that may apply to the project.
That’s why understanding the land before you fall in love with the house plans is so important.
First Things First: Know Your Slope
When we’re talking about mountain construction, “steep” isn’t just a matter of looking at a lot and thinking, Yep, that’s a hill.
Slope is measured as a percentage. A 25% slope, for example, rises 25 feet over a horizontal distance of 100 feet.
And once you get into steeper terrain, the percentage can climb quickly.
In Buncombe County, hillside development regulations place specific limits on disturbed and impervious areas. For individual lots with slopes between 25% and 35%, the maximum gross area disturbed is 30%, with impervious surfaces limited to 15%. For slopes greater than 35%, those limits drop to 15% disturbed area and 8% impervious area.
That matters because “disturbed area” isn’t just the footprint of your house. It can include things such as driveways, septic systems, grading and other site work.
In other words, you can’t necessarily look at a large mountain lot and assume there’s plenty of room to work with.
The Lot May Dictate the House
One of the biggest mistakes we see people make when considering a challenging lot is starting with the house they want and trying to make the property accommodate it.
On a steep lot, it’s often smarter to work the other way around.
Start with the land. Then design the house around it.
A good site plan considers:
- Where the natural slope runs
- The steepest portions of the property
- The best building area
- Access for construction equipment
- Driveway grade
- Stormwater drainage
- Septic and well locations, where applicable
- Retaining walls and other structural requirements
- Views and solar orientation
- Trees worth preserving
- Required setbacks and buffers
- How much grading will actually be necessary
The City of Asheville Has Its Own Steep-Slope Requirements
If you’re building within Asheville city limits, the City’s Unified Development Ordinance includes specific regulations for steep-slope development. The City also uses mapping and development-review tools to identify regulations that may apply to a particular property.
Asheville’s steep-slope regulations can limit the amount of land that can be disturbed based on slope and elevation. The City also has additional considerations around trees and vegetation in certain steep-slope areas because removing vegetation can increase runoff and contribute to erosion or slope instability.
This is important because clearing a mountain lot isn’t as simple as bringing in a bulldozer and creating a big flat pad.
Sometimes the best approach is to leave the mountain alone as much as possible.
Buncombe County Steep-slope Requirements
Buncombe County has specific hillside development regulations that become particularly important once you get into slopes of 25% and greater. The rules are more nuanced than simply saying “you can’t build on a steep slope.”
Here are the key provisions that are most relevant to a custom-home project:
25%-35% slopes
- Maximum 30% of the lot may be disturbed
- Maximum 15% may be impervious surface
Slopes greater than 35%
- Maximum 15% of the lot may be disturbed
- Maximum 8% may be impervious surface
Those calculations apply to individual-lot improvements, including the house, driveway, well and septic systems, as well as recreational improvements such as pools and tennis courts.
There are also additional requirements that become important on steeper sites.
