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june 2004

Registered Landscape Architect and Licensed Irrigator

How to Build an Intensive Residential Green Roof
By Jennifer Appel
All photos and drawings courtesy Jennifer Appel

Design By Jennider Appel

Above Ground Parking Garage Intensive Greenroof at the Humble Oil Marriott, Houston, Texas, May 24, 2004

When most people envision a green roof, they think of grass or small plants on top of a structure. Today, Green Roofs are covered with maturing trees, year-round flowering plants, and chef requested herbs for culinary treats.

People are astonished to see 12’ trees growing on top of the former Humble Oil Building now Marriott Hotel structure here in Houston, Texas, with more than 5,000 flowering plants. Eyes widen when I tell them that the entire landscape receives only two minutes of water a day in Houston’s triple digit summers!

Aerial Shot Above the Parking Garage Design by Jennifer Appel

Left: Aerial Shot of the Humble Oil Marriott; Right: Flowering Planters, May 24, 2004

To keep this highly visible 10,696 cubic foot hydroponic project looking optimum, I visit the site every Friday for about two hours to perform organic maintenance! Since its inception, there has never been a pesticide application, plant replacement, or a color change out. (To see a slideshow presentation of the Humble Oil Marriott, go to the green roof page.)

Center Fountain at The Courtyard by Marriott, design by Jennifer Appel

Center Fountain at The Courtyard by Marriott

In 2003 I retrofitted the original parking garage that was built in 1921 on top of the historic Humble Oil Marriott in downtown Houston using an extremely successful 8 pound per cubic foot soil-less media for the green roof. My goals were simple:

1) create a constantly flowering low maintenance hydroponic roof
2) grow high end residential landscape plantings on a commercial building
3) use organic fertilizers to increase flowering while reducing the watering requirements

Humble Oil Marriott, Houston, Texas Flowering Trees and Shrubs

Intensive Greenroof with Flowering Perennials and Trees; Design by Jennifer Appel

Patrick Carey’s Green Roof story here of June 2003 posed a challenge. He mused that most of the green roof technology today is built for commercial applications, but no one is designing residential sites with green roofs in mainstream metropolitan areas, where the real money lies.

I believe that to create a successful environment for residential green roof systems people need to want them first! Monetary benefits are the most popular reason to install a green roof. Properly designed, we could cut the heating and cooling costs for a residence in half. A roof could last a lifetime with no replacements. Everyone could have free rain water as irrigation water. We could increase the habitable space and value of every property. We could reduce grocery bills by planting herbs and vegetables where most pests do not go. Designed and installed appropriately, a green roof could pay for itself within the first year!

To achieve the goal of a residential green roof that can be easily installed in a suburban or urban setting, I needed to look at both existing and proposed types of construction. Existing construction is every house that exists today. Many of the single and double story homes have roof structures that can not easily be altered. However, most homes in my area have detached garages.

Detached garages are only considered at 10% of the home value for insurance purposes. So if a tree falls on your house, the policy will pay up to the value of the policy to fix your house. However, if a tree falls on your detached garage, it is only worth 10% of the house value. If a carport was installed to attach the house to the garage, the garage would be valued at the house value, too.

Phase One: Green Carports and Decks
At many land strapped client homes we are starting to create waterproof carports that double as decks. Clients add planter boxes, handrails, televisions, stereos, and watch fireworks from the upper deck. For existing homes, the current answer is clear, build up! Add decks and carports and great living roof systems to confined residential houses to maximize your habitable space and your property value. Some of the many benefits of a green deck include increased vegetable and herb garden area, living space, landscaping space, property value, insurance benefits, as well as walking in a dry environment from the house to the car. A reduction in heat gain and glare through windows from covered driveway paving and lower residence heating and cooling costs may also be benefits from a green carport. The grade level area, once dead space, often creates an inviting overflow area for entertaining guests.

By designing uncommon lightweight planter boxes into the handrail system above the deck material, we can smoothly transition people from grade level gardening to second and third floor gardening. Properly designed, these green decks may reduce the heating and cooling costs by shading part of the residence.

Click here to enlarge Click here to enlarge

Click on each ACAD  drawing for a larger image of the Green Deck by
Jennifer Appel

After the clients have already incorporated heat and glare films, I get many requests to build a pergola or patio cover over a series of huge west facing bay windows. The shade awning business is a high profile moneymaker with thousands of people requesting covered seating. With space at such a premium in so many places, instead of selling clients pergolas, we could design a green deck instead for roughly the same cost with better benefits.

Most landscapers can build a deck. Most irrigators can string drip tubing on a separate valve to the deck for the planters. These construction measures are in place. What we want to do to start the transition is to illustrate how to turn an average deck into a green (roof) deck.

Green Deck 12-Step Recipe
1) Build one carport that doubles as a deck. I recommend TREX on steel for less maintenance. Pick any material, shape, or size to fit your client’s needs. Slope sheet metal or galvanized aluminum under the deck, to direct the water to gutters.
2) On top of the deck, build a standard 4’ fence, including a gate to the stairs or elevator, around the edge for security purposes.
3) Attach planter boxes 3’ wide and 3’ deep inside the outer 4’ wood security fence.
4) Insulate the planter boxes with Tyvek or Styrofoam.
5) Overlap and staple Bio Barrier fabric (nodes point in) to the inside of the wood planter box to keep the plant material roots from breaking the form. (Bio Barrier is a filter fabric with chemical nodes to keep roots from growing through the fabric.)
6) After wrapping the entire inside with the Bio Barrier, overlap and staple Enka drain filter fabric to the inside of the wood planter box to allow for drainage and keep the planting media in place. (I recommend commercial grade roofing staples to do this.)
7) Fill the planters with 100% screened horticultural grade perlite. (Wait until the winds are low.)
8) Add drip irrigation tubing on top of the screened horticultural perlite. (Holes go down to keep them from getting clogged.)
9) Add a ½” of compost and ½” of earthworm castings over the perlite to keep it in place.
10) Add plants.
11) Attach bench seating, lighting, or other lightweight structural amenities that will not blow away.
12) Fertilize your new garden with a non-synthetic chemical twice a month.

Enjoy your new deck garden!

Phase Two: Green Garages
Once green carports and green decks have become a proven part of mainstream requirements for residential homeowners, green garages could be the next phase. For proposed construction, the architect, landscape architect, and construction contractor need to be involved in the initial consultations with the client. Phase Two of residential green roofs might start with flat roof green garages utilizing green decks to connect the residence and garage. Allowing the residence to remain as a normal roof structure, the green garage roof would increase the habitable space while creating a private landscape retreat above the enclosures of residential fences, concrete, and walls.

I support green garages as a second phase. As long as this technology is new, contractors and do it yourselfers who do not want to pay for professional services will try to cut corners to increase cost effectiveness. I promise that it costs less to do it right the first time than to do it twice. I would rather see a poorly constructed garage roof fail than a residential roof in a tract home subdivision if a homeowner chooses an inexperienced contractor.

Design Requirements for a Green Garage
To create a green garage that should not fail, start with a slightly sloping flat roof. Have an engineer design the structure to support the required live and dead load weights. For wind protection, build the façade of the garage four feet higher than the roof, as architectural ornamentation much like most "Main Street" buildings from the early 1900’s. These structural wing walls will be used to support the outer edges of the planting areas.

Slope the flat roof to sheet drain to one side utilizing ‘leave outs’ in the wall structure for sheet drainage. Make sure that your landscape design allows for all of the planters to drain to the same place. Add standard waterproofing and a protection board. Make sure that you test your waterproofing at this time. We used Grace waterproofing and protection board at the Humble building. Add gutters to the drain the water to the back side of the garage. Instead of sending the gutter water to the drainage system, direct the water into 2 or more structural cisterns at the back side of the garage. These cisterns will later be used for your irrigation/sprinkler water. There are many manufacturers of cisterns. Pick one that suits your needs.

To build your green garage, lay out a landscaping plan to include sitting and walking spaces on the roof that make access to your planting area easy. Most people can comfortably reach about 4’ into a planting area. Try to design an area that is functional and beautiful so that maintenance will be efficient. Most all paving manufacturers make a lightweight walking surface for roof applications. Don’t forget lighting and other electrical, solar, or gas amenities that you might want in the future.

Building the Intensive Green Garage Roof
Once you have a design that you like, create 3’ tall planters on top of your roof that are no wider than 4’ from the outer walls. Insulation wrap and duct tape Bio Barrier (nodes up or in) to the entire waterproofed area including the walls. After completing the Bio Barrier wrap, add a layer of Enka Drain on top of the Bio Barrier with duct tape. Make sure that the Enka drain completely covers everything below it so that the planting medium does not leave the planting area. Follow the manufacturer’s recommendations. Unlike a green deck that should drain to a lower catch pan, do not create any holes in the waterproofing!

Next, calculate the cubic area for the planting area by multiplying the square feet by the depth of the area. I recommend a planting depth between 2 and 3 feet because most intensive greenroof plants' root systems grow to a depth between 2-4 feet in soil-less media. However, 3’ is adequate to grow most all types of intensive flowering plant material. To fill your green garage with soil-less planting medium, order (1/2 of our cubic foot number) horticultural perlite, 1/8”-1/2” in size. Perlite is the white “beads” that you find in the planting mix when you buy 4” plants at the nursery. Add the remaining 1/2 of the cubic foot number in USPS packing peanuts. I used the cheapest packing peanuts I could find. You DO NOT want to add sand, soil, or any other materials other than those stated in this article on your green garage. The blend of horticultural perlite and USPS Packing peanuts weighs less than 8 pounds per cubic foot. With plants, our calculations illustrate a wet weight of about 23 pounds per cubic foot for our media selection. Sand, soil, vermiculite, peat, compost, and potting soil weigh between 20-140 pounds per square foot wet without plants. Using heavy water holding soil media may cause your garage roof to collapse when it rains regardless of the structural capability, drainage slope, and waterproofing.

Fill the entire planting space with 50% horticultural perlite and 50% packing peanuts. Lay your drip tubing with the holes down on top of the soil-less media. Add a ½” of local (weed free) compost and ½” of earthworm castings and plant your plants. Wiggle Worm Soil Builder and Worm-o-licious are two of my favorite worm casting companies.

Low Maintenance Designs
For ease of maintenance, space your plants appropriately. Appropriately spaced plants means if a plant grows to a full mature size of 3’ tall and 3’ wide, plant it with enough room to grow to its full mature size without crowding another plant; in other words, plant "A" needs to be spaced 3' apart from the center of plant "B"'s center - such that the neighboring 3' wide plant "B" grows to meet the drip line of plant "A" without crowding either plant. Planting appropriately will reduce pests and diseases, increase the air flow around your plants, create a low maintenance design, and reduce the watering and fertilizing requirement. Small plants will perform better in confined spaces using this system. In other words, DO NOT OVERPLANT!

So, in a small space, such as a green garage, deck, or carport, you might need a total of 30 one-gallon plants. Additionally, only plant plants that can fit their mature root zone in the space provided. As an example: Don't plant oak trees in a 3' square area - properly fed, they will grow far too large for their intended space with potentially disastrous results.

Either purchase full size five-gallon plants, (for the less experienced gardener), or use one-gallon plants and let them fill in the blank spaces. Planting too many small plants to make a project look full will cause a failure! I’m not a fan of shorter varieties of bamboo on the ground. However, it makes a clean fence-like backdrop when planted deeply on a green garage and allows for wind protection for color and herb plantings in the interior. Lightweight colorful plantings are the key to a beautifully flowering green roof and they are much easier to lift to their new home.

Free Irrigation Water
To me, the easiest method for reducing maintenance is a sprinkler or irrigation system. If you currently have an irrigation system, add a separate pressure regulating zone valve to the main line and add a 1” PVC schedule 40 line up to the green roof deck. Add drip tubing from the 1” line for all your watering needs. Set the timer to water this zone 2-4 minutes a day. The water will drain through the planting area each day. The plants should dry out each afternoon and be ready for their next glass of water in the morning. (If your roof structure is taller than 12’, your water pressure will need to be augmented for every 12’ increase in elevation from the Main line.)

Some people have the time to enjoy hand watering their new landscape. I do not. If you do not have an existing irrigation system, here is an easy method to construct one for your roof. Rain water is free and generally low in salt. For a low cost non-potable irrigation system, use the adequately sized structural cisterns that hold the rain water from your roof as your main source of water. Add a 3” PVC schedule 40 pipe connecting the bases of the cisterns. Waterproof the connections and add a ball valve or hose bib tap in the 3” pipe for maintenance and drainage. Add an overflow at the top of one of the cisterns. Connect the overflow to your drainage system or route the overflow away from all structures. (Before a storm, you will want to empty the tanks and refill with fresh new rain water.)

To create your irrigation system, add a sump pump to one of the connected cisterns. Add a 1” PVC schedule 40 line from the sump pump to the planting area and run drip tubing from the 1” line in the planters. Add an electronic timer with a battery back up to the adequately sized sump pump. Set the timer so that the landscape gets adequate water for the requirements of your plants every day. (Drip tubing prefers a pressure regulator and daily use to be maintenance free.)

Free Foundation Watering System
In subdivisions that have a lot of foundation problems due to heavy clay soils, you can create a free perimeter watering system around your foundation utilizing the water from the cisterns. (I grew up in a tract builder house on a fault line that required foundation leveling, twice, because we did not use our free rainwater efficiently to regulate the moisture content under the foundation.)

To decrease the maintenance of your garden even more, add a fertilizer tank to your irrigation system. A fertilizer tank will feed your plants through your sprinkler system. Each time your irrigation system waters your plants, the plants will also get fertilized. Once a week or twice a month, add a non-synthetic liquid fertilizer into the tank. Why do you want a non-synthetic product? Synthetic chemical fertilizers may kill your plants after one application. (See the Miracle Gro vs. Shultz vs. Pet Friendly tests at Synthetic fertilizers may create high levels of salt, and adding high levels of salt to your plants will require more water to grow your plants.

I use Jennifer’s Landscape Vitamins to grow the Humble plants more than 4 times faster than the normal average with 1/5th the water.  Jennifer’s Landscape Vitamins are safe for pets, children, and the environment. Too much of a good thing is not healthy, but it is extremely rare for an organic fertilizer to kill plants. In one test, we over fed our plants by 400% and the fertilizer did not harm a single bloom. Organically fed plants require ½ - 1/5th the water of chemical landscapes. If your plant leaves start to turn yellow – turn down the amount of water they get and refill your fertilizer tank. Yellow leaves mean that the plants are OVERWATERED and the soil-less media has been depleted of 13 essential nutrients that plants need to grow!  * Publisher's Note: Please read my question below to Jennifer about how and why she created Jennifer’s Landscape Vitamins as a business.

Intensive Residential Green Roofs
This same method for creating a green garage can be duplicated for a green roof on any well designed residential or commercial structure. The company products I used for the Humble Oil Marriott intensive greenroof include: Schundler Perlite Company; Bio Barrier; Enka Drain; Jennifer’s Landscape Vitamins; Hunter; Rainbird; TREX; Wiggle Worm Soil Builder; Worm – O - Licious.

Following are press releases about the Humble Oil Marriott building when it was finished: Long Silent Houston Landmark Reborn, and New Life for HoustonLandmark.

Intensive Greenroof at the Humble Oil Marriott, Houston, Texas, May 24, 2004
Jennifer forces the plants to bloom year-round by feeding them weekly

I welcome your comments and suggestions!

Ms. Appel is a registered landscape architect and licensed irrigator in Texas, with a BLA from Texas A&M in 1993. She is the owner of, a design build firm specializing in innovative and low maintenance landscape architectural solutions to high end residential and commercial drainage clients in Houston, Texas. 

Jennifer is also the developer and proprietor of Jennifer’s Landscape Vitamins.  Ms. Appel can be reached at 713.263.1682 or at

LSV:  How did Jennifer’s Landscape Vitamins (formerly Pet Friendly™ Fertilizers) get started?

Jennifer Appel:  "As a landscape architect, working side by side with landscape contractors, I was charged with specifying products for my client's homes. Although not totally organic, I was practicing IPM (Integrated Pest Management) in the late 1990's. IPM programs usually involve organic applications with acceptable pesticide or herbicide applications to reduce pests and disease outbreaks. I killed my cat from a spot pesticide application. After several discussions with my veterinarian, I started looking for a fertilizer that was safe for pets, children, and the environment. I found no 'fertilizers containing all 16 essential nutrients' on the market that did not include a potentially toxic ingredient. I learned that even organic products may contain naturally occurring, yet lethal ingredients. (For reference visit

Faced with the challenge of creating an all-natural fertilizer that would out perform synthetic fertilizers while eliminating the need for pesticide and herbicide applications has been entertaining. After surveying veterinarians to ascertain how common lethal and non-lethal reactions to fertilizers and pesticides are, Jennifer’s Landscape Vitamins entered the retail market in May 2003. (You can read and download the survey at Incorporating Jennifer’s Landscape Vitamins Fertilizers may assist architects to qualify for up to 11 LEED points."

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