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Site Attributes: Size, Shape, and Topography
Mastering Site Analysis: Unlocking Value in Real Estate
Chapter X: Site Attributes: Size, Shape, and Topography
Introduction:
A thorough understanding of site attributes is fundamental to accurate real estate valuation and development planning. This chapter delves into the critical site characteristics❓ of size, shape, and topography, exploring their impact on property utility, value, and highest and best use. We will examine relevant scientific principles, mathematical relationships, and practical applications, enabling you to effectively analyze these attributes in real-world scenarios.
1. Site Size:
1.1 Importance of Site Size:
Site size directly impacts the potential uses of a property, development density, and overall value. Different land uses have optimal size requirements.
1.2 Measurement Units and Conversion:
Common units include square feet (sq ft), acres, hectares, and front footage. Accurate unit conversions are essential for consistent analysis.
1 acre = 43,560 sq ft
1 hectare = 2.471 acres
Front Footage: is the measured footage of a site that abuts a street, lake or river, railroad, or other feature recognized by the market.
1.3 Economies and Diseconomies of Scale:
As site size increases, the unit price (e.g., dollars per square foot) often decreases due to economies of scale (lower cost per unit of development). However, very large sites may experience diseconomies of scale due to increased❓ infrastructure costs, longer development timelines, or difficulty in marketing a large quantity of units at one time.
1.4 Surplus Land vs. Excess Land:
- Surplus Land: Land that is not needed to support the existing or proposed use of the site and cannot be sold off separately for independent use. It may add some value, but not at the same unit price as the primary land.
- Excess Land: Land that is not needed to support the existing or proposed use and can be sold off separately as an independent parcel. It has its own highest and best use. Excess land must be treated separately in the valuation process with consideration of the cost in time and money to legally separate the parcels if they are not already separated.
1.5 Application:
- Comparable Sales Analysis: Adjustments for site size differences are crucial in sales comparison analysis.
Percentage Adjustment = ((Subject Site Size – Comparable Site Size) / Comparable Site Size) * Market Adjustment Rate
Example:
Subject site: 50,000 sq ft
Comparable site: 40,000 sq ft
Market adjustment rate: 10% per 10,000 sq ft
Percentage Adjustment = ((50,000 – 40,000) / 40,000) * (10%/10,000 sq ft) = 0.1 *10% = 1% positive adjustment.
2. Site Shape:
2.1 Influence of Shape:
Irregularly shaped sites can present challenges for development, affecting building layout, access, and usable area. Shape impacts density, construction costs, and marketability.
2.2 Common Shape Classifications:
* Regular: Rectangular, square. Simplest to develop.
* Irregular: Triangular, L-shaped, trapezoidal. May limit development options.
* Flag Lot: A lot with a narrow strip of land connecting it to the street. Often has limited access.
2.3 Shape Metrics:
* shape index❓: Relates the perimeter of a site to its area. Higher shape index indicates a more irregular shape.
Shape Index (SI) = Perimeter / (2 * √(π * Area))
A circle has the lowest possible SI of 1.0. A square has a SI of 1.13
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Area-to-Perimeter Ratio (A/P): Indicates the relative efficiency of a shape. A higher A/P ratio suggests a more usable shape.
The A/P ratio can be useful for comparing lots of different sizes.
2.4 Corner Influence:
Properties with frontage on two or more streets may have a higher or lower unit value than neighboring properties with frontage on only one street.
2.5 Application:
* Building Placement and Setbacks: Shape dictates the placement and orientation of buildings, influencing setbacks, parking, and landscaping.
* Subdivision Design: Shape considerations are critical in subdivision planning, ensuring efficient lot layouts and street access.
3. Site Topography:
3.1 Definition and Importance:
Topography refers to the surface features of a site, including elevation, slope, and drainage patterns. It influences development costs, accessibility, views, and environmental factors.
3.2 Topographic Data Sources:
* Topographic Maps (US Geological Survey - USGS): Provide detailed elevation contours, water features, and man-made structures.
* Digital Elevation Models (DEMs): Computer-generated representations of terrain. Used for 3D modeling and slope analysis.
* LiDAR (Light Detection and Ranging): Remote sensing technology that creates high-resolution topographic data.
* Site Surveys: Professional land surveys providing precise elevation and feature locations.
3.3 Key Topographic Attributes:
* Elevation: Height above sea level. Affects views, climate, and drainage.
* Slope: The degree of inclination of the land surface. Expressed as a percentage or angle.
Slope (%) = (Vertical Rise / Horizontal Run) * 100
Slopes are categorized into the following:
* Level - 0-5%
* Gentle - 5-10%
* Moderate - 10-15%
* Strong - 15-30%
* Steep - 30%+
- Aspect: The direction a slope faces (e.g., south-facing slopes receive more sunlight in the Northern Hemisphere).
- Drainage: The natural flow of water across the site. Important for preventing flooding and erosion.
3.4 Impact on Development:
* Construction Costs: Steep slopes increase excavation and foundation costs. Flat sites are generally easier and cheaper to develop.
* Accessibility: Slope affects road construction, driveway grades, and pedestrian access.
* Erosion and Sediment Control: Steep slopes require measures to prevent soil erosion during construction.
* View Potential: Elevated sites often command premium prices due to enhanced views.
3.5 Geology and Soil Analysis:
3.5.1 Geological Conditions: composition of surface soil and subsoil—are important for both improved properties and agricultural land.
3.5.2 Soil Composition and Classification: Soil is a mixture of mineral particles (sand, silt, clay), organic matter, water, and air. Soil composition affects drainage, fertility, and load-bearing capacity. The soil triangle is used to classify soils based on the proportions of sand, silt, and clay.
3.5.3 Bearing Capacity: The ability of soil to support the weight of structures. Measured in pounds per square foot (psf) or kilopascals (kPa). Different soil types have different bearing capacities. Soil conditions affect the cost of development and therefore the property value.
3.6 Floodplain and Wetlands Analysis:
3.6.1 Floodplains: Areas adjacent to rivers or streams that are subject to periodic flooding. Defined by FEMA (Federal Emergency Management Agency).
3.6.2 Wetlands: Areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and under normal circumstances does support, a prevalence of vegetation typically adapted for life in saturated soil conditions.
3.6.3 Impact on Development: Floodplains and wetlands are subject to strict regulations that limit development options. Construction within these areas may require permits, floodproofing measures, or mitigation.
3.7 Application:
* Cut and Fill Calculations: Determining the amount of earth to be removed (cut) or added (fill) to achieve desired grades.
Cut/Fill Volume = (Area of Grid Cell) * (Average Cut/Fill Depth for the Cell)
* Slope Stability Analysis: Assessing the risk of landslides on steep slopes.
* Stormwater Management: Designing drainage systems to manage runoff and prevent erosion.
* Septic Suitability Testing: Determining if the soil is suitable for a septic system.
4. Plottage Potential:
Plottage is an increment of value that results when two or more sites are combined to produce a larger site with greater utility and probably a different highest and best use.
5. Conclusion:
Site size, shape, and topography are fundamental attributes that significantly impact property value and development potential. By understanding the principles outlined in this chapter, you can effectively analyze these attributes, identify opportunities, and make informed decisions in real estate valuation and development.
Chapter Summary
Site Attributes: Size, Shape, and Topography
This chapter emphasizes the critical role of site attributes—size, shape, and topography—in real estate valuation and site analysis. These characteristics significantly influence a property’s utility, desirability, and ultimately, its value and highest and best use.
Size: Site size directly affects value, generally exhibiting an inverse relationship with unit price (e.g., price per square foot or acre). Larger sites often command lower unit prices due to economies of scale and market demand, while smaller sites typically have higher unit prices. Optimal size is use-dependent, and appraisers must analyze market sales data of varying lot sizes to understand the local market’s perception of value for specific uses. The concepts of excess land (land that can be separated and sold independently) and surplus land (land that cannot be sold separately and does not have an independent highest and best use) are crucial for proper valuation, especially when determining whether the sum of the parts equals the value of the whole.
Shape: Irregularly shaped sites, including corner lots, present unique challenges and opportunities. Corner influence can be either positive or negative, depending on the intended use. Commercial properties often benefit from increased visibility and accessibility on corner lots, while residential properties may suffer from increased noise, reduced privacy, and higher maintenance costs. The concept of plottage describes the value increment that can occur when combining two or more sites, creating a larger parcel with greater utility and a potentially different highest and best use. Conversely, subdivision can yield a lower value per square foot in the marketplace.
Topography: Topography encompasses a site’s contour, grading, drainage, geological characteristics, and overall physical❓ suitability for development. Steep slopes can impede construction, while inadequate drainage can limit a site’s usefulness. topographic❓ maps from the US Geological Survey (USGS) provide valuable information on elevation, water bodies, and man-made features. Understanding local terminology for topographic features❓ is important for accurate description. Geological and soil analysis are essential to determine suitability for building, septic systems, and the potential need for specialized foundations. Soil surveys from the US Department of Agriculture provide data on soil composition. Structural distress such as cracks in walls or foundation might be evidence of geotechnical or soils problems. Appraisers must consider floodplain maps from FEMA and analyze the presence of wetlands, understanding the relevant regulations and potential impacts on value. Expert consultation with engineers, geologists, and soil scientists is often necessary to fully assess a site’s topographical characteristics and their impact on value. Understanding the impact of threatened and endangered species that can be present during development.
