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Following is my summary and critique of the "Sustainable Sites" section of the LEED 2.2 New Construction Reference Guide, Second Edition, Sept. 2006. My commentary on the Reference Guide can be found in the red boxes below, and within each of the chapters linked immediately above.
The idea is to reduce construction-related pollution and degradation, including soil erosion and sedimentation of waterways, as well as to limit the production of dust.
The required strategy is to make a plan — the so-called Erosion and Sedimentation Control (ESC) plan — that follows local or 2003 EPA "Construction General Permit" guidelines (whichever is more rigorous).
Specific suggestions include:
seeding or mulching of the ground (either temporary or permanent)
building earth dikes, fencing to contain silt, sediment traps, and so on
Picking an appropriate site is here given a mostly negative slant: do not build on farmland, parks, undeveloped land in a flood plane, habitats for threatened or endangered species, wetlands (or sites near wetlands), or undeveloped land within 50 feet of water bodies (like lakes, rivers, etc.) that could otherwise be used for recreation or industry.
This last point is a bit puzzling: LEED advises that buildings should not be sited near water bodies that might be used for industry instead. While this might be sensible from the standpoint of economic growth, it's not clear how it relates to the goal of sustainable development, as the unsustainable industrial use of water bodies is itself a major issue.
The recommended strategy is to site buildings on previously-devloped sites, even those that are in flood planes, or near water bodies.
It is not clear why building in the flood plane, or near a water body, becomes desirable simply because the site has already been inappropriately developed. The same environmental hazards exist, whether such a site has or hasn't been previously developed.
Urban sites with already-developed systems of infrastructure are preferred, as such development leaves alone natural habitats and so-called greenfields outside those areas. There are two choices for this credit, both of which require building on a previously-developed site:
For choice "1," the local urban density must be at least 60,000 sq.ft. per acre (corresponding to 2-story "downtown"-type neighborhoods) — this density refers to both the actual development density as well as the regional density measured within a circle centered on the site with 9π times the area of the site (i.e., about 28 times the area). The density calculation excludes roads, parks, and similar undeveloped areas.
For choice "2," the site must be within 1/2 mile of a residential area and within 1/2 mile (with pedestrian access) of 10 basic services, including things like banks, grocery stores, day care, laundry, and so on.
The LEED commentary suggests that such development improves worker productivity and occupant health: productivity because workers spend less time driving (as if workers somehow automatically live near their places of employment simply because a workplace is located within 1/2 mile of some residential area; and as if workers with shorter commute times spend the "extra" minutes thereby obtained by arriving early at work and donating free labor to their employers); and health because of increased physical activity as people walk the 1/2 mile to the grocery store and carry back bread and pork chops to their homes (as if 1/2 mile walks seriously count as physical activity; and as if this small-town model of local grocery stores and daily walks to shop for fresh vegetables corresponds to actual life as we know it — this is clearly written by people who have never experienced the unrelenting exhaustion brought about by actually working, shopping, preparing meals, and raising families).
LEED introduces the concept of trade-offs here: the idea that there may be negative environmental consequences for following the advice leading to a particular credit. Specifically, the commentary notices that those who build in "dense" urban areas may encounter "limited open space and possible negative IAQ aspects such as contaminated soils, undesirable air quality or limited daylighting applications." But LEED has no mechanism for subtracting points corresponding to these, or other, potentially negative consequences of a particular development. Instead, each "credit" is considered independently, potentially leading to certification of a building that has numerous negative environmental features.
Note that maximizing urban development (high density) is rewarded here, while maximizing open space (low density) is rewarded elsewhere (see Credit 5 in this section). The implicit argument that greenfields, unlike urban areas, should remain as undeveloped as possible only makes "sense" in the context of a planet carved up into parcels of privately owned real estate, each developed according to the calculations of its owner. Such a situation precludes examining the logic of consolidating development, even in greenfields.
Finally, LEED defends urban development by criticizing "sprawl," using two familiar arguments: first, commuters spend more time commuting (in cars), and may require additional cars to support their suburban lifestyles; second, by developing projects in cities, cities are restored and invigorated, which creates "a more stable and interactive community." Unfortunately, this second argument lacks historical perspective. It is precisely the congestion of urban areas that leads to the development of interstate highways and the redefinition of growth centered on the nodes created at the intersections of such highways (see Joel Garreau's 1991 Edge City). The ideal of living 1/2 mile from both one's workplace as well as "basic services" abstracts from the reality of work under capitalism: the city is useful precisely to the extent that physical proximity to a range of services and labor makes sense to a particular business; the attraction of such places to those who need to find work has a well-documented trajectory, but one that is entirely contingent upon the presence of businesses whose decisions to locate in a particular place have to do only with calculations concerning profitability. Whether workers move to follow jobs, or capital moves to reduce its costs, has nothing to do with supporting a "more stable... community." "Community" is a historically-bounded and unintended consequence of urbanization, neither its driving force nor its inevitable result. The suburban Desperate Housewives have as much sense of community as the urban Friends. Of course, both of these examples are fictional, but no more so than the "community" imagined in this LEED credit.
Note that a business may need to locate in an urban area for reasons that have nothing to do with preserving greenfields or fostering "community," and there may be no impact on "community" or on the preservation of greenfields (i.e., the nature of such a business may preclude development outside of urban areas so that greenfields, in any case, were never threatened) as a result of such development, yet the LEED credit is still awarded.
A point is given to projects that remediate damaged (contaminated) sites; this not only fixes broken sites, but reduces the need to develop previously-undeveloped land. The key advice given here is to (1) "[i]dentify tax incentives and property cost savings," (2) weigh various "concerns" (i.e., negative perception of site based on perceived health risks, and potential liability), and (3) make sure the cost of clean-up (accounting for government subsidies) doesn't threaten profitability.
State intervention to protect profitability is mentioned here: The LEED commentary references CERCLA (the 1980 Comprehensive Environmental Response, Compensation, and Liability Act, a.k.a. the "Superfund") which funds governmental intervention to remediate contaminated sites; the use of "incentives" at all levels of government is also mentioned as a way of encouraging "brownfield redevelopment by enacting laws that reduce the liability of developers who choose to remediate contaminated sites." From this, it is clear that sustainable development often does not make economic sense to businesses without state intervention (where such intervention takes the form of subsidies or is directly legislated as a specific requirement).
There are four points possible here:
Public Transportation Access requires that the project be 1/2 mile or less from some form of commuter rail, or within 1/4 mile of at least two bus lines;
Bicycle Storage & Changing Rooms requires bike racks for one twentieth of a commercial/institutional project's "peak" user population and showers for one two-hundreths of the project's full-time-equivalent (FTE) occupants, or just covered bicycle storage (for 15% of occupants) for residential projects;
Low-Emmision & Fuel-Efficient Vehicles has several options that require various amounts of "preferred parking" (i.e., parking that is closest to building entrance, or with discounted price), approved vehicles (includes gas-electric hybrids), and alternative fuel stations. Specifically, either approved vehicles made available with preferred parking for 3% FTE occupants; or preferred parking for approved vehicles, but no vehicles actually provided, for 5% total parking; or alternative fuel stations to service 3% of parking capacity; and
Parking Capacity requires that 5% total parking be provided as preferred parking for carpools or vanpools while not exceeding the minimum parking allowed per zoning (this for non-residential projects), or (for residential projects) that the parking provided be no more than the minimum allowed by zoning and that shared vehicle usage (e.g., car-share, carpools, ride boards, etc.) be supported; or (for either residential or nonresidential) that no new parking be provided.
Reducing on-site parking can put a strain on surrounding neighborhoods. This contradiction is noted in the LEED commentary, without any meaningful attempt at resolution. The recommendation that "any on-site parking reductions should be carefully balanced with community needs to avoid needlessly burdening surrounding neighborhoods with excessive street parking" can be translated as: "In some cases, you really should forget about this credit and increase on-site parking to be consistent with actual anticipated conditions; however, we'll still give you your LEED rating point if you decide instead to reduce parking and follow our guidelines, even if you're only displacing the required parking off-site, thereby providing no positive environmental impact through reduced car use and simultaneously making life worse for your neighbors."
There are two possible points here, both encouraging open space.
Protect or Restore habitat requires that greenfield sites (i.e., those found in a "natural state") be left in their natural state except, of course, for those parts of the site where things are to be constructed, i.e., where buildings, roads, walkways, parking lots, and site utilities are planned plus a certain distance surrounding all these buildings, roads, walkways, parking lots, and site utilities (within which the natural state can be similarly dismantled). The permitted distances within which construction is permitted are as follows: 40 feet for buildings, 10 feet for walkways, 15 feet for roadways, and so on. Non-greenfield sites must be restored or protected in such a way that at least half of the area outside of the building itself consists of native or adapted vegetation.
For dense urban sites earning SS Credit 2 (see above), "restoring habitat" is reformulated so that Credit 5 can be realized when only 20% of the non-building site area (instead of the 50% requirement applied typically) is restored with appropriate vegetation. Vegetated roof surfaces count toward this 20%.
Maximize Open Space has various options for compliance, depending on zoning ordinance stipulations: (1) reduce buildings and roads and/or [?] provide vegetated open space so as to exceed zoning requirements by 25%; or (2) where no zoning exists, provide as much vegetated open space as building footprint; or (3) where zoning exists but has no open space requirement, provide vegetated open space for 20% of the site area; or (4) for urban sites earning SS Credit 2, the requirement for vegetation is relaxed so that as much as 75% of the vegetated open space can be "pedestrian oriented hardscape;" vegetated roof areas count as well.
The LEED commentary's economic justification for open space is articulated as follows: "Even in cases where rent values are high and the incentive for building out to the property line is strong, well designed open space can significantly increase property values." This type of justification has no logical underpinning, in as much as the same premise could generate the opposite conclusion. The point is that development is based on calculations to maximize profitability, where the provision of "open space" may or may not pay off for the developer. Furthermore, increasing the value of property is not the same as increasing profits: a developer can build an entire facade of gold bricks to create a building of extraordinarily high value while going broke at the same time.
Note that for restoring habitat in urban sites, the 20% criteria could result, at the extreme, in a rather small vegetated area which is nevertheless awarded a LEED point. (For example, consider an urban building with a footprint of 50'x100' on a 50'-wide site that is 120' deep. This leaves a non-building site area of 1,000 sq.ft. and a required vegetated area of 200 sq.ft. which can be satisfied by a 4'-wide strip of planting at the back of the site, or on the roof.)
Also note that for certain campus settings, where no zoning applies, some open space may be designated at a remote location. This allows open areas already slated for preservation to generate LEED credits.
Two credits are possible here, one for "quantity control" and the other for "quality control." The intent for both credits is to manage stormwater so that it conforms as much as possible to the natural hydrology of the site.
Quantity control requires either that peak discharge rates and quantity don't exceed one- and two-year 24-hour storms (where site imperviousness is less than or equal to 50%), or that measures are taken to produce a 25% reduction of stormwater runoff from two-year 24-hour storms (where site imperviousness is greater than 50%). In the former case, one can create a "stream channel protection... and quantity control" plan as an alternate to actually limiting the discharge rates and quantity to that of one- and two-year 24-hour storms.
Various strategies are suggested, including the reduction of impervious cover, using vegetated roofs, building water detention and retention features, and storing and reusing "harvested" rainwater. Using harvested rainwater for irrigation generally requires a minimum pressure of 15 psi; since stored water creates a pressure of 0.43 psi per foot of height, harvested water must be stored at least 35 feet above the discharge point if intended to be used for irrigation without supplementary pumps.
Quality control requires a plan to increase permeable surfaces and to capture and treat at least 90% of the stormwater runoff from an average year's rainfall. The basic criteria for treatment is to remove 80% of "total suspended solids" (TSS) from the runoff.
Suggested strategies include "nonstructural" methods such as rain gardens and vegetated swales, as well as constructed wetlands, vegetated filters, etc.
Of interest is the definition of regional rainfall types:
|Annual rainfall||Amount of rain that will create runoff equivalent to 90% annual rainfall|
|≥ 40"/year = humid watershed||1"||20"-40"/year = semi-arid watershed||3/4"||< 20"/year = arid watershed||1/2"|
Two credits are available here, one for non-roof areas, and the other for the roof surface itself. The basic idea is to reduce the area of dark surfaces which otherwise would absorb sunlight and re-emit heat energy, disrupting the microclimate and upsetting human and wildlife habitats. Specifically, urban heat islands can raise local temperatures 10-degrees F, increasing energy use for HVAC.
Non-roof mitigation measures can be met in two ways: either deal with at least half of the site "hardscape" (roads, walkways, patios, etc.) by using combinations of shade, reflective paving materials (with "solar reflectance index" or SRI ≥ 29), and/or "open-grid" pavement; or put at least half of parking under cover or under ground (with roofing material for any such structure having SRI ≥ 29).
Roof options are as follows: either have 75% of roof conform to reflectance criteria (i.e., SRI of 78 for low-slope; 28 for steep-slope); or have 50% of roof be vegetated; or have combined high-reflectance (albedo) and vegetated roof such that total SRI plus veggie area ≥ SRI area ÷ 0.75 + veggie area ÷ 0.50.
The solar reflectance index (SRI) is defined by black = 0 and white = 100.
Note that meeting these requirements reduces air conditioning loads (which makes sense for quite a few buildings), but can increase heating costs. In other words, meeting the requirements for this credit may, in some cases, increase energy use. Also note that in cases where governmental entities have already intervened to make the use of so-called "cool roofs" mandatory, this LEED credit is given for something that would have happened in any case.
The rationale for this credit has three parts: to improve night sky access, improve night visibility (less glare), and minimize disturbance of nocturnal habitats. There is both an "interior" and an "exterior" component that must be met:
|Zone||Max. footcandles at site boundary||Max. footcandles @ distance (feet) beyond site boundary||Light emittance at or above horizontal|
|LZ1 - Dark
Park, rural setting
|0.01||0.01 - anywhere beyond||none permitted|
|LZ2 - Low
|0.1||0.01 - 10' beyond||2%|
|LZ3 - Medium
|0.2||0.01 - 15' beyond||5%|
|LZ4 - High
Major city centers, entertainment districts
|0.6||0.01 - 15' beyond||10%|
IESNA = Illuminating Engineering Society of North America
ASHRAE = American Society of Heating, Refrigerating and Air-Conditioning Engineers
The recommendations for low-reflectance surfaces (to minimize light pollution) contradict the recommendations in Credit 7 (Heat Island Effect) for high-reflectance surfaces. There is no attempt at resolution.
First posted Nov. 2, 2007; last updated 25 January, 2008 [minor re-formatting]