What is a Green Area Ratio (GAR)?
Per the District of Columbia Municipal Regulations definition 600.1, Green Area Ratio (GAR) is “the ratio of the weighted value of landscape elements to land area. The GAR score relates to an increase in the quantity and quality of environmental performance of the urban landscape.”
“GAR sets integrated environmental requirements for landscape elements and site design that contribute to the reduction of stormwater runoff, the improvement of air quality, and the mitigation of the urban heat island effect.” – DCMR Section 600.2
In layman’s terms, GAR is simply the minimum amount of landscape surface (mulch, grass, permeable pavers, etc.) that a property is required to have – expressed as a decimal as it’s the ratio of landscape elements to total lot area.
What is the purpose of a Green Area Ratio (GAR)?
The purposes of the GAR score are to:
- “Implement a value-based system of requirements for environmental site design that provides flexibility in meeting environmental performance standards; and”
- “Promote attractive and environmentally functional landscapes.”
Is a Green Area Ratio (GAR) Plan required for my property in Washington, DC?
See below GAR Trigger Decision Tree to determine if your project in DC will require a GAR Plan. GAR requirements only apply if you are planning interior renovations, an addition, or a new building and will need a Certificate of Occupancy for these property improvements.
Is Green Area Ratio (GAR) required for Residential Zoned Properties?
If your property improvement project is in an R (Residential) or RF (Residential Flat) zoning district in DC, then GAR requirements are not applicable and you do not need a GAR Plan for your project. For these R (Residential) zones, you will still need to meet a minimum percentage of pervious surface depending on the R- zoning district and lot size. See Figures 1 and 2 below for the pervious surface percentage requirements per R zone and lot size.
If your interior renovation, addition, or new building project in Washington, DC is not in an R or RF zone then you will need to meet a Green Area Ratio somewhere between 0.2 to 0.4, depending on the zone. For minor interior renovations and additions with total project construction costs less than 100% of the existing assessed building value, GAR requirements do not apply.
You can look at Table 1 below to see the specific GAR requirement for your property’s zone. If you do not know what zone your property is in, you can search for your property address on Property Quest DC. This Green Area Ratio value is often referred to as a “GAR Score.”
Are Historic Structures exempt from Green Area Ratio (GAR) Requirements?
Historic Structures are only exempt from GAR requirements if the proposed addition is less than 50% of the existing gross floor area. If the proposed addition is more than 50% of the existing gross floor area of the historic structure, then GAR requirements will apply and a GAR Plan will be required for the project.
What area of my property must meet the required GAR Score?
All of the area inside your property lines, according to your official lot dimensions, must be factored into the GAR score as the “Lot Area.” The Green Area Ratio will determine how much of your lot area will need to be composed of various landscape elements.
What Landscape Elements can be used to meet the GAR Score?
Typical Landscape Elements used to meet the GAR score are landscaped planting areas, bioretention planter boxes, vegetated green roofs, trees, and permeable pavers. For a full list of approved landscape elements to count toward the GAR Score, see Table 2 below.
As you will notice, each landscape element has its own multiplier that varies from other elements. This is because landscape elements such as trees and plants have a greater environmental value than groundcover or soil area.
How is the Green Area Ratio (GAR) Score calculated?
The GAR score is a ratio of landscape elements multiplied by their respective multiplier and divided by the lot area. As shown in the graphic below, a combination of landscape elements can be utilized to meet the overall GAR score for a particular property.
Can I use public space or an off-site area to meet the required GAR Score?
No, all landscape elements to be counted towards the GAR score must be inside the property lines. Each individual lot will have to meet the Green Area Ratio requirement for its respective zone.
Who can prepare a Green Area Ratio (GAR) Plan for Permits?
A GAR plan must be prepared by a “Certified Landscape Expert,” which is a person who holds one of the following certifications or licenses in valid and good standing:
- Landscape Architect licensed by the District of Columbia.
- International Society of Arboriculture Certified Arborist
- Maryland Certified Professional Horticulturist
- Landscape Contractors Association (MD, DC, VA) Landscape Industry Certified Technician
DeMarr Engineering has Certified Landscape Experts on staff to guide you through the process and to help prepare a GAR Plan for your project.
Example GAR Plan Prepared by DeMarr Engineering in Washington, DC
On this project in the Adams Morgan neighborhood of Washington DC, our in-house Certified Landscape Experts designed a combination of bioretention facilities, plantings, vegetated “green” roof, and permeable pavers to meet the most stringent GAR requirement of 0.40.
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