Hillside Development Overlay Zone: Part Two

The purpose of the Hillside Development Overlay Zone (HDZ) ordinance was initially promulgated to prevent Tucson’s beautiful lower foothills and slopes ringing the perimeter of our valley from becoming densely populated with homes, driveways, and scarring, thus creating a natural and visual nightmare for us all as we enjoy the natural desert and mountain setting that we love. At the same time there was a recognition of some resident’s desire to live as close as possible to the naturally beautiful, rugged, and remote areas that drew many of us to want to live in Tucson. HDZ regulations was a way of accommodating and planning to meet these diverse interests.
Before delving into the details of HDZ, let me answer a frequently asked, HDZ-related question regarding the development of Ventana Mountain Estates. Visitors and residents alike wonder how Pima County could allow the hills above Loew’s Ventana Canyon Resort to be developed in such a dense, visually impactful way. Simply speaking, under today’s guidelines this development would be prohibited and impossible. However, the subdivision was platted in the early 1970’s before the county realized the ramifications of hillside building. HDZ rules apply to land parcels recorded after July 1, 1976.
According to Pima County, the Overlay Zone applies to “any land parcel with an average cross slope of 15 percent or greater or to land parcels with any slopes of 15 percent or greater.”
Average cross slope is a means of determining the average amount of slope in mountainous, highly-sloped land by using a specific mathematical formula. This is determined through calculations studying the topography of a site and done by civil engineers or licensed surveyors. The results become the basis of how much grading can be done on a parcel, where development should be placed, and what part of the lot must be set aside and designated as undisturbed open space.
A parcel that has a combination of flat, rolling, and some 15% sloped land, which is typical of many custom lots in Tucson, is the second category of land subject to HDZ regulations. Although average cross slope calculations will not need to be done, limitations of grading will apply.
The formula to determine the amount of gradable area on lots of 1 to 4 acres to build a single family home is 30% of the first acre, or 10% of the lot, whichever is greater. This encompasses the total area of all grading (other than the enclosed area of dwelling unit) for driveways, parking areas, yards, swimming pools, walls and accessory structures. For example, on a 1-acre lot (43,560 sq. ft) that would allow approximately to 13,068 square feet (30%) as a maximum gradable area. On a 3.31 acre site, the formula would allow for a gradable area of approximately 14,400 square feet or 10% of the overall lot size.
HDZ regulations also establish limits when developing near Pima County’s protected peaks and ridges which are specifically identified and mapped throughout Pima County. The regulation states that “there shall be no development within a horizontal radius (map distance) of 150 feet from a protected peak point or 150 feet from a protected ridgeline.”
These are some of the highlights of the issues a purchaser must think about when buying a sloped parcel within Pima County. The full set of HDZ rules and regulations go into much greater detail and cover additional areas. Typically, your custom builder or architect assists with the kind of analysis needed to make development decisions on this kind of land. Pima County employees in the HDZ Office can also be very helpful in guiding you and answering questions.
In Tucson, there are opportunities to build and live on some of the most magnificent vacant parcels in the Southwestern United States, perched high overlooking the entire Tucson Basin, contiguous to the national forest or park land, or in and around the mountain ranges that surround Tucson. With time, patience, money, and the earnest intention to be guided by the right professional help, you may be able to enjoy the unique lifestyle of living on this type of home site.

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