Green parking may be new to you. In previous editions of this column discussions have been put forward that parking lots are going green and landscape codes are helping to push this trend. I've defined green parking lots as places that "do environmental work," and urban spaces that serve several purposes beyond storing cars.
Greening parking lots is a trend that landscape architects need to pay attention to, and for one good reason. The most familiar space to most Americans is not the backyard garden, neighborhood park or the town square. It is the parking space they use every day. Yes, this is American's most used outdoor space and it is in general a hot, exposed, oily slab of reinforced concrete or uneven and pitted asphalt.
Shade calculations may be presented in graphic form as seen in Exhibit A of the Sacramento Code Design Manual. This parking lot example calculates 73 percent canopy coverage for the 23-space Parking Grove, a segment of a green parking lot under design in California's Napa Valley.
Source: Sarah Smith, Abbey Associates, Inc.
This column takes a look at a community codes that address parking lot shading. One of the first principles behind greening parking lots is to cover it with an overhead canopy to reduce the urban heat island effect.
Shading Codes
A few parking lot shading codes have been around since the early 1980s, but such codes are extremely rare across the country. Most landscape codes merely require a certain number of trees in parking lots, not a specified amount of shade. Shading codes go beyond tree planting for beautification and require calculations of shadow patterns, the extent of that pattern and best means for positioning trees to achieve the desired shading effects.
This green parking lot design includes permeable parking bays that stormwater drains into; trees buffering adjacent lands areas; bioswales for runoff (surface and subsurface flow); perforated curb stops to feed runoff into bioswales; roof runoff draining into French drains; shallow depression rain garden; pedestrian paths between buildings; and a green roof.
Source: Adam McGovern, Abbey Associates, Inc.
Calculating Shade
The Sacramento city code (Title 17, Zoning, Division II, Development Standards Chapter 17.68 Landscaping and Paving Regulations, § 17.68.040 Tree Shading Requirements for Parking Lots) is among the best landscape codes in the country in regard to reducing the urban heat island effect with trees. This code drafted in 1983 sets standards to lower the amount of solar heat gain and increase solar reflectivity emanating from urban parking lots. This code sees trees as environmental improvements to the parking lot environment.
The code has standards for surface parking facilities, expansion of existing parking lots and specific standards for tree shading. The language of the code sets forth standards and procedures for shade calculations, creating shading plans and drafting specifications for installation and maintenance.
The designer must prepare the plans, do the calculations and certify that shading complies with the standards set forth in the design manual, titled Parking Lot Tree Shading Design & Maintenance Guidelines (dated November 2001). The technical essence of these calculations are based upon determining shade patterns and the extent of coverage over all surface parking facilities, including all surfacing on which a vehicle can drive, all parking stalls and all driveways and drive-through service lanes within the property.
The central technical standard to this code, and several like it, require that from the tree planting dates, there should be 50 percent shade coverage after 15 years. The code assumes a calculation based upon a midday sun angle and sun altitude for an approximate latitude of 38 degrees, 52 minutes. Design guidelines provided by the city set forth a plant list whose square footage of a tree crown has been estimated at 15 years. This can be easily calculated on the plan. Existing trees or nearby shade producing street trees may also be calculated into the 50 percent shade standard. Covered structures built over parking areas are also included in the calculation.
Tree specifications are set forth in Appendix A of the design manual. They include 35, 30, 25 and 20-foot radius tree canopies after 15 years. These are considered maximum crown diameters to use in the calculations. Also provided to the designer in the guidelines are the height, growth rate, roots character and tree form. These diameters will of course vary across the country with species, soils, moisture and climate.
The landscape plan must provide a tree symbol list, tree type designation (or plant species), tree quantity and the square footage of the parking area. The later must include the design of all interior planting areas, walkways, travel lanes and parking spaces. The figure on p. 24 shows a section of a parking lot being calculated for shade. Calculated on the plans are the total surfaced area (TSA), shade area required (SAR), total tree shade (TTS) and the total shade area provided (TSAP) after 15 years of growth. Shading credits for individual trees are calculated as 100 percent, 75 percent, 50 percent, and 25 percent canopy coverage. Overlaps are not counted more than once. Calculations may be presented graphic form as seen in Exhibit A of the design manual (above left). This parking lot example calculates a 73 percent canopy coverage for the 23 space Parking Grove, a segment of a green parking lot under design in California's Napa Valley.
