How much do Green Roofs weigh?


The average extensive Green Roof with 3-4 inches of soil weighs about 20 pounds per square foot when saturated. This is slightly more weight than gravel ballast. Intensive or mixed-use Green Roofs are custom installations and weights vary greatly.

What is the process for getting a Green Roof?

Step 1 - Determine if your rooftop can handle the load. You will need an architect to certify that your roof can hold 20 pounds per square foot in addition to snow loading in order to get your building permit. Please see Are You Roof Ready? to help determine if your roof can handle the weight of a Green Roof. If you want to Green Roof a new building, you probably already have an architect on hand to do this assessment. If you want to retrofit an existing building, you will need to hire an architect to certify the structural loading. This can be expensive to do. D.C. Greenworks can refer you if you don't know an architect.

Step 2 - Design your Green Roof and determine specifications. If you are working with an architect, he or she may draw plans or write specifications for your Green Roof system. If not, D.C. Greenworks will provide this service for you as part of contract. We will work with you to design and build the Green Roof that fits your needs and your site. If your building can support the weight, we can also build intensive rooftop landscapes, patios, pergolas and the like into your Green Roof design.

Step 3 - Waterproof the building with the right membrane for the Green Roof and the site. D.C. Greenworks works with local waterproofing companies to make sure your building is watertight and ready for your Green Roof. If you don't have a waterproofer, D.C. Greenworks can refer you, but you should always shop for the best price. You can also install a leak detection system at this point. For waterproofing specifications, please download here. Remember that waterproofing your building is a separate cost from building your Green Roof. This makes it most cost-effective to Green Roof when you are already replacing your waterproofing.

Step 4 - Install the Green Roof. Once the waterproofing is sound, DC Greenworks will install all of the Green Roof components, and plant the roof according to your preferences and the horticultural needs of your site. We can also install patios, pergolas and other features into your Green Roof at this time.

How much maintenance is involved?

In the first year, your Green Roof plants will be small, and there will be a lot of bare soil that might grow weeds. If your Green Roof is beneath trees, this is especially true. During the first year, your Green Roof will need weeding at least twice, and may lose up to 10% of its plants. DC Greenworks provides two visits in the first year as part of your contract where we weed and replace plants, but if you wish to weed more often (or want us to!), it won't hurt a bit.
Once the plants have grown in, and there is no bare soil visible, the Green Roof will be virtually self-maintaining. Yearly fertilization with pelletized compost or slow-release fertilizer carefully spread around the plants should be all that your Green Roof needs.

How much do Green Roofs cost?


Green Roofs have an economy of scale. The bigger the Green Roof, the cheaper the square foot cost. This is because the materials and soil used in Green Roofing are specially made just for Green Roofing, and are cheaper to produce and deliver in bulk quantities. Another major cost factor is labor. If your rooftop is inaccessible for heavy equipment and vehicles, we may have to build your Green Roof by hand, which drives up cost greatly.
In the residential range, extensive Green Roofs can vary from $12-35 per square foot, but if you have a tiny Green Roof to build, the total cost of the project can be relatively low. In the commercial range, extensive Green Roofs can vary from $5-15, depending on the size and the difficulty of construction. Mixed-use and intensive Green Roofs are custom installations, and cost varies greatly. Please see Are You Roof Ready? to determine if Green Roofing is right for you.

Are there any tax incentives, grants or rebates for Green Roofing?


At this time, there are no tax incentives for developers or homeowners. Though this may change in the near future. If you are a developer, there are a couple of subsidy options open to you in Washington, D.C. The D.C. Department of the Environment has some grant funds available to help subsidize Green Roofs on large-scale public-use developments. These grants are competitive and not available to all. However, developers who can show that Low-Impact Development strategies such as Green Roofing and bioretention can take up the first half inch of storm water on the site can apply to use the LID in lieu of conventional stormwater management practices. Because Green Roofs and bioretention usually cost significantly less than sand filters and other conventional management techniques, developers can save a lot of money on a project by thoughtfully incorporating a Green Roof into their building design.