Friday, May 27, 2011

Sustainable Site Planning Basics

One of the most important and effective ways to create sustainable designs is taking a collaborative approach.  Ideally all of the project stakeholders (owner, architect, engineers, contractors, etc) are brought together before design begins and the design process can be a completely collaborative process where all parties are able to provide valuable input based on their expertise. The reality, however, is that this rarely happens, especially on smaller scale projects. In my experience the typical process involves the owner hiring an architect who later hires the engineers and finally the contractor is brought on board late in design or after the design is completed. Often the architect creates preliminary designs for the project including site layout, building location and orientation, elevations, floor plans etc. Sometimes this occurs with little or no input from the engineers. When the engineer comes on board the opportunity for collaboration and changes to the design is diminished. However, I realize there a lot of reasons that the process can evolve this way and I understand that it will continue to work that way on many projects.

After years of trying to shoehorn LID and green practices into site layouts created by architects I decided that providing some framework for creating sustainable site designs was the best approach to take. In doing that I created a presentation that I take on the road to architects. This post is that presentation in distilled form. The intent of both the presentation and this post is to provide architects and other design professionals with a toolbox for sustainable site planning and therefore facilitate better site designs. Below I have included 7 brief topics on sustainable site design.

What is a sustainable site plan?
My definition - "A site plan that has the least environmental impact while still meeting the client's project goals." It's not sustainable if it only parks half the cars that the project needs and costs twice as much as budgeted. Just like any other design it has to be framed within the typical project parameters, but it also includes consideration of the environmental impacts.

Site Selection
Site selection can have a significant impact on the environmental impact of a project site. Some specific paramters to consider when selecting a site include:
  • Avoid flood plains - continued development in natural flood plain areas has contributed to increased flooding, decreased flooding and increased soil loss.
  • Provide buffers for bodies of water - Development around bodies of water such as streams and wetlands should be limited and include buffers of undisturbed areas of 50'-100' or more.
  • Avoid greenfields - greyfields and brownfields are often less expensive to develop, place less stress on infrastructure and limit the environmental impact of developing previously undeveloped sites.
  • Transportation - the impact that transportation of people and goods to a site has can be significant. Try to select sites that encourage the use of public and non-motorized transportation.
Site/Building Layout
The simple act of proper building orientation can create energy savings of up to 25%. As little as 8 degrees of rotation can have an impact. Consider the following when siting and orienting buildings.

  • Elongate the plan on the east/west axis
  • Maximize north and south exposure for daylighting
  • Minimize east and west facing windows
  • Orient most populated areas to the north and south
The above items are good general guidelines but keep in mind that extreme climates may warrant different practices. For instance in extremely cold climates limiting windows on the north side may create energy savings that outweigh the benefits of the daylighting that they provide.

Impervious Surfaces
Increasing the imperviousness of a site can have a tremendous effect on the water cycle. Impervious surfaces limit groundwater recharge, increase pollutant loads and runoff and create a heat island effect.    Its important to limit the impervious areas on site to the minimum. Doing this often improves the aesthetic of the site, reduces the environmental impact and saves money.  Below are some things to consider in order to reduce site imperviousness.
  • Minimize parking areas
    • Zoning code minimum or less
    • Incorporate compact car spaces when possible
    • Reduce lane sizes
  • Provide plantings in and around parking areas
  • Implement Green Roofs
  • Implement pervious paving options
    • Pervious pavement/asphalt
    • Pervious concrete
    • Permeable pavers
    • Grasspave systems
Grading Considerations
The environmental impacts of mass grading a development or building site is often overlooked.  Site grading destroys the natural ecosystem present within the soil.  This ecosystem provides systems to break down pollutants, provide nutrients for biota, support insect and animal life and numerous other benefits.  It takes many years for the soil to recover from mass grading and sometimes it never does.  There is also the temporary or permanent impact of soil erosion which pollutes waterways and washes valuable soil off site.  Whenever possible we should try to limit grading operations to the distances beyond constructed items as shown below.

  • < 10 feet beyond surface walkways, patios, surface parking, and utilities
  • < 40 feet beyond the building perimeter
  • < 15 feet beyond primary roadway curbs
  • < 25 feet beyond constructed areas with permeable surfaces (pervious paving, stormwater  detention, and playing fields)
Stormwater Management
Stormwater runoff is one of the most significant environmental impacts of a developed site. But it also provides one of the greatest opportunities for sustainable design.  All of the items listed above help to limit the amount and speed of stormwater leaving the property and also contribute to improving the water quality as well.   However, developing a site can significantly alter the hydrologic cycle for the property and surrounding area.  Steps can and should be taken to maintain the pre-development hydrology or even to improve it.  Many municipal regulations require that the post-development runoff rate does not exceed the pre-development rate, but do not address runoff quantity.  These regulations are largely flood control based and do not address groundwater recharge and the hydrologic cycle.  The Low Impact Development techniques shown below can be used to mimic the pre-development hydrology.
  • Raingardens/Bioretention
    • 6"-12" deep
    • 8%-10% of site area
    • <1/2 acre drainage area
    • up to 2 acres possible
    • landscape islands
    • 4'-10'+ between parking rows
    • 8'-10' for double loaded rows
  • Wetlands
    • 6"-12" deep
    • large drainage areas (often > 25 acres)
    • minimum 6”-18” permanent pool depth
    • excellent water quality control
    • provides wildlife habitat
  • Grass swales/infiltration trenches
    • up to 5 acres drainage areas
    • 1%-4% slopes
    • low maintenance
    • improves stormwater quality
  • Green roofs
    • well suited for urban and ultra urban areas
    • intensive and extensive types
    • < 20% roof slope
    • improves stormwater quality
    • intercepts and stores rainfall (up to 50%)
    Landscape Design
    Landscape design is often ignored in the initial planning stages and is tacked on at the end of the project.  This is unfortunate and discounts the many benefits that proper landscape design can have beyond aesthetics.  On the other hand, improper landscape design can have significant negative effects such as excessive potable water use and erosion.  Listed below are a number of items to consider during the site planning phase and throughout the design process.

    • Limit potable water use
      • Use Native Species
      • Place landscape areas to receive runoff
      • Use captured rainwater
    • Shade large hardscapes
    • Shade buildings in summer, allow sunlight in during winter 
    • Place and design landscape areas to filter and clean stormwater
    • Raingardens in parking areas
    • Bioretention rather than retention ponds
    Resources
    Below are some excellent resources for additional and supporting information about sustainable sites.

    1. The Sustainable Sites Initiative
    2. The United States Green Building Council
    3. Portland Sustainable Stormwater Management Program
    4. US EPA 
        1. Stormwater management
        2. LID Techniques
    5. The Center for Watershed Protection
    6. Prince Georges County Maryland - Division of Environmental Protection
    Slides from my Sustainable Site Planning Basics Presentation

    All of the techniques listed above are just items to consider when performing site planning.  As you can see the items impact the architect, civil engineer, MEP engineers, contractor and owners.  Ultimately, the best way to produce sustainable site plans is to get the entire design and construction team together early and often in the development process.  

    3 comments:

    1. I have just done an export and sbo
      worked out the conversion rates for each bucket and i find them very similar. IE as a % site speed isn't making a difference to conversionsboasia

      ReplyDelete
    2. All you describe sounds like Landscape Architecture and the Sustainable Sites Initiative !!!

      ReplyDelete
      Replies
      1. Yes - I think that the Sustainable Sites Initiative is a great program! I have also found that landscape architects are often more in tune with "green" site techniques than civil engineers. I strongly encourage civil engineers to work closely with landscape architects whenever possible.

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