Density figures misleading Posted April 23, 2001 Analysis & Commentary by J.C. Huntington

The backers of the South Village describe the density of the South Village by saying there are  “less than two houses per acre,” or “1.9 dwelling units per gross acre”

However, based on current South Village Planned Area Development (PAD), the true density of the South Village is about 4 houses per acre, not 1.9.

The key is the understanding what the backers meant when they say the density is “1.9 dwelling units per gross acre,” lies in the phrase “gross acres.”

The backers of the South Village figured the density by dividing the number of houses into the “gross” acreage of the South Village – in other words, the total area of the project.

But the total area of the South Village includes golf courses, washes, mountain slopes, the area of the Town and Village centers, the area used for roads, and so on.

Since it is not practical to build houses on golf courses, in washes or in the middle of roadways, the true density of the South Village must be figured by dividing the number of houses by the number of acres available for building them.

Those that believe that it is misleading to imply the density of the South Village is “1.9 dwelling units per gross acre” when the true density is closer to 4 houses per acre have a point.

Imagine what your banker would say if you applied for a loan figuring your “gross hourly wage” by dividing the number of hours worked into your before-tax income instead of your actual take-home pay.

Details follow.

• The total area of the South Village is 4,600
• The area used for golf courses, washes, mountain slopes etc. is 1610 acres
• The area for Town and Village Centers is 273 acres
The number of dwelling units is 8,517

Since 1610 acres would be used for golf courses, etc. and 273 acres would be used for Town and Village centers, 2717 acres remain (4,600 -1,610 – 273 = 2717).

If  8,517 houses were built on 2,717 acres, each lot would be 0.32 acres in size (2,717 ÷ 8,517 = 0.32).

There are 43,560 square feet in an acre, so 0.32 of an acre is 13939.2 square feet (0.32 X 43,560 = 13,939). In round figures, this would be a lot 100 by 139 feet:

Now we need to figure the area that will be used for roads between the lots.

If we assume the easement for a road is 50 ft. (a fairly standard easement) and take half the easement off of the lot size (because the other half of the easement would come from an abutting lot) we end up with a lot size of 100 by 114 feet:

 Figure 1: Two Lots With No  Road Between Them Figure 2: Two Lots With 50 '  Wide Road Between Them

A lot 100 by 114 feet is 11,400 square feet.   Since there are 43,560 square feet per acre there will be 3.82 lots per acre (43,560 ÷ 11,400 = 3.82).  In round figures: 4 houses per acre.

 An aerial view The image below shows this sort of lot size when viewed from above: Phoenix, Arizona Circa 1997 Image Courtesy of U.S. Geological Survey

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