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July 2017
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green roof basics

What are the major benifts of green roofs?

  • Stormwater Management
  • Aesthetic Improvement
  • Improved Air Quality
  • Increased Energy Efficiency
  • Increased Roofing Membrane Lifespan
  • Improved Health and Well-Being
  • Increased Biodiversity
  • Food Production
  • Local Job Creation
  • Educational Opportunity

What are the green roof standards? 

Currently there is only one reconized green roof standard, which comes out of Germany; the Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau (commonly referred to as the FLL).  These guidelines include industry standards for testing the weight, moisture, nutrient content, and specification of growing media.   Currently the American Standard Testing Methods (ASTM) is working to create a guide for American Green Roof Standards.

How much does a green roof cost? 

This is a tricky answer because the cost of a green roof can vary due to a number of factors.  Some of the factors are size and scale of the roof, accessibility and height from the ground, depth of growing media, pant selection, and freight costs.  Each site is unique and will present its own opportunities and challenges.

How much do green roofs weigh?

The weight of a green roof also can vary due to many factors.  The depth and type of growing media, plant material, type and weight of other green roof components.  We base our green roof weight on a fully vegetated and saturated scenario.  A typical 4 inch green roof weighs approximately 30 pounds per square foot.   There are a number of different green roof options based on site conditions, including lightweight systems.

How steep of a slope can a green roof be?

The suggested maximum slope for a green roof is a 7:12 pitch, or 30 degrees.  There are a number of ways to stabilize the green roof in a slope application including; meshes, cleats, and panels.  Take a look at dc greenwoks’ first sloped green roof!

Is irrigation needed on my green roof?

Irrigation on a green roof is dependent on climate, growing media, and plant selection.  During prolonged periods of drought and extreme temperatures, irrigation (temporary or permanent) can be critical to the survival of the roof.  There are a number of irrigation applications that can be applied to the roof including overhead/spray, drip, or irrigation buried under the surface where it can be in direct contact with the root systems.

What type of waterproofing membrane do I need on my roof?

There are a number of waterproofing membranes that are suggested and compatibly with green roofs.  Polyvinyl chloride (PVC), thermoplastic polyolefin (TPO),ethylene propylene, diene monomer (EPDM) and modified bituminous membranes some of the most common membranes used in green roof construction.  Every roof membrane should be tested for water tightness prior to the green roof installation.



green roof plants

What type of plants should go on my roof?

Plant variety should be based on hardiness zones and regional climate.  Green roofs are often dominated by sedum (succulents) which have served to  extremely hardy  drought tolerant plants.  On green roofs with a deeper media depth, a greater variety of plant species can be incorporated into the design.

How long does it take to fully cover my roof?

Typically a green roof takes 18-24 months to full establish itself.  This is often considered to be 2 full growing seasons.  For this to happen it is critical that the roof is properly  installed and maintained.

Can I walk on my green roof? 

Yes and No.  The roof has to be capable to handle the live load capacity. If the roof is accessible and has the adequate capacity walkways, patios and decks can be integrated into the design.  As for the vegetated areas, many plant species can take light foot traffic but a walkable surface should be provided. This can be achieved through pavers, gravel, and decking.

Why is green roof maintenance like?

Green roof maintenance is required to establish the roof.  During roof maintenance visits, drains, gutters, edging, and other roof components should be inspected and well kept.  It is important to carefully weed out invasive plant material to allow the green roof vegetation to establish.  Upon establishment, periodic maintenance visits are required to ensure the success and health of the plants.  dc greenworks  provides and performs maintenance programs on all of our green roof installations.  Contact us now to set up a maintenance program.

What happens to my roof in the winter?

A green roof will respond to winter similar to the that of a typical garden on the ground level.  Depending on plant selection many of the plants will enter a dormant state during the winter.

rain barrels

What is the process of getting a  rain barrel in DC?

Call dc greenworks today!  We are here  assist you in the selection and installation your rain barrel!  Contact Abe Wiener at

What are the advantages of a  rain barrel?

  • Rain barrel captured water is not subject to community watering restrictions.
  • Naturally soft water with no additives to irritate your plants.
  • Save money on your water bill.
  • Reduce water pollution in our rivers and lakes by reducing stormwater runoff.
  • Save money on your sewage treatment bill by decreasing the amount of water going into the sewer system.
  • Decrease energy consumption used to treat waste water and delay building/expanding waste-water treatment plants.

How do I use the water in my rain barrel? 

Rainwater can be used for a variety of things such as:

  • Watering your garden, composter, trees, or flowers.
  • Irrigating your yard.
  • Washing your car.
  • Please note that it is not potable or not safe for consumption

How much water is running off my roof?

Here is a useful table for the volume of water generated by three different storm events – see page 2 for “Imperial” units of measure: Chart.pdf

For the mathematically inclined: to calculate gallons of runoff generated in a 1” rain for a chosen area of
roof, use the following formula:

Volume = (Area) (1”) (7.48/12)

For this formula, volume is measured in gallons and area in square feet.
In most cases the rain barrel will not be large enough to capture all of the
water from a downspout, so to keep the foundation of your home safe
from water damage it is important to install an overflow mechanism or an additional rain barrel.

How much area can my rain barrel service?

A number of variables, including slope, soil, and pressure, will determine the area that your rain barrel will service with a soaker hose.  Experimentation will be required.  The above formula may help somewhat to determine the roof area that your barrel will service with an inch of water.

How much water will I save with a rain barrel?

The best way to measure it is by the size of a barrel: If you have a 132 gallon barrel, you can save up to 132 gallons of water every time your rain barrel fills!

What are the dimensions of the RiverSides RiverSafe rain barrel?

The RiverSides barrel measures 51″ inches high, 27 1/4″ in diameter.  Rear clearance will be needed for the filter and diverter box; see the RiverSides site for a visual.

How do I change the appearance of my rain barrel?

  • You can incorporate your rain barrel into your landscape, using plant material to blend in with your barrel.
  • Construction of a fence orstructure around your barrel.
  • Paint is an option, but make sure you purchase paint that in compatible with the materials of your rain barrel.


rain/habitat gardens

What is a rain garden?

A rain garden is an attractive garden with a special purpose; to reduce the amount of rainwater and pollutants that enter our local streams and waterways.  A rain garden is a garden designed to direct and capture the rain from your impervious surfaces (roof, driveways, sidewalks, ect.).  This reduces the quantity of rainwater that enters and overflows our storm drain systems.  Rain gardens are typically designed and planted with plant species that are native to our region that can tolerate both dry and wet conditions, have deep root systems which can improve soil conditions, and add aesthetic value to a property.

How do I determine the size of my rain garden?

Rain gardens can vary in size.  Each rain garden will be different based on the site conditions and amount of rainwater runoff that will enter the garden.  Rain gardens should be sized such that they are able to capture all of the rainwater that falls in a 24 hour period.  To adequately size your rain garden we have supplied suggested techniques.

Are rain gardens a place where mosquitoes breed?

No. Typically mosquitoes need 7-12 days to lay and hatch their eggs.  A rain garden will only retain standing water for a day at most.  In fact mosquitoes are more likely to lay their eggs in bird baths, gutters, and storm drains than in a rain garden.

What is the difference between a rain garden and a traditional garden?

From the surface a rain garden looks fairly similar to a traditional garden.  Typically rain gardens are a depressed bowl-shaped gardens that filter nitrogen, phosphorous, and sediment though a highly engineered soil and plant material.  It was was is under the surface that defines a rain garden, through multiple filtration layers designed to also act as a water storage area.

What qualifies a habitat garden?

A habitat garden is a garden that is designed to invite and sustain wildlife.  There are four essential design factors that are needed to meet the requirements of a habitat garden; to provide a water source, shelter, food, and provide a place to raise an animals young.  These gardens are typically designed with plant species that are native to our region.