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FOTD living green roof

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ENGR215 Project Page in Progress
This page is a project page in progress by students in Engr215. Please refrain from making edits unless you are a member of the project team, but feel free to make comments using the discussion tab. Check back for the finished version on {{{1}}}.


The purpose of the project was to educate Nature Center visitors on the benefits of living green roofs, to enhance the aesthetics of the Nature Center, and to inspire others to build their own green roofs. The Dune-Gineers Green Roof was built at the Friends of the Dunes Nature Center by students at Humboldt State University Engineering 215 class.


The Friends of the Dunes is a non-profit organization, and their Coastal Nature Center is a place where they promote green solutions by educating visitors. They work to protect and preserve the natural habitats of the dunes. The Friends of the Dunes originally planned to have a living green roof put on their back terrace, so the terrace was built to be able to hold a heavy garden. They tried to get a living green roof built, but the quote given to them by the hired company was too expensive. When they were later presented with the opportunity for student engineers to build a green roof for much cheaper, they decided to give us the job.

Problem statement

To build a 500 square foot roof on the back awning of the Nature Center.

Problem Analysis and Criteria

Criteria Weight Description
Aesthetics 10 The roof must look as professional as the rest of the Nature Center.
Support Local Plants 9 Must be able to keep native plants alive during the summer months.
Cost 3 Entire design must cost less than $400.
Weight 5 The roof must weigh less than the roof can handle. The lighter the final design, the better.
Safety 5 Must be designed to be accessible for maintainable and weeding.

The Solution

The conservative design option is engineered with initial and maintenance costs in mind, as well as, building restraints and criteria. Concrete blocks are used for the retaining wall, with the components of the green roof layered behind. The base layer will be an inch of gravel, followed by a filter sheet used as the separation layer. Four inches of sand are used as the growing medium and are placed on top of the filter sheet. An erosion control mat will be used on the top to hold down the sand in stormy conditions.

How to Build

An additional layer of waterproofing paint is added to make sure no leaks occur. Concrete blocks are carried up on a twelve-foot or higher ladder, and stacked two high around the edge of the roof, four inches from the gutter. Gravel is then brought up in buckets and spread to a height of one inch. The separation fabric is placed on top, leaving 4 inches of extra cloth along the edges. The cloth is not wide enough to completely cover the bottom of the roof, and needs to overlap by one inch at any seams. Four inches of sand is then added on top of the separation fabric, excluding the sides. Along the insides of the blocks and against the wall, extra gravel is added to a thickness of one inch and a height of four inches. The extra four inches of separation fabric is then used to separate this column of gravel from the four inches of sand. Extra sand is added to the roof to fill in any low points on the roof. Once the layers are in place, a micro sprinkler system is installed. The erosion control blanket is then placed on top of the sand. On the edges of the roof it is pushed down into the sand to hold it in. Stakes are taken from the surrounding green roof where the erosion control blanket has decomposed and are used to hold down the new blanket.


Size Material Source Cost ($)
1 Hydrostop Protection Layer On site 0.00
500 sq feet Protection Fabric Miller Farms 60.00
1.4 cb yards Gravel Miller Farms 70.00
500 sq feet Separation Fabric Miller Farms 60.00
42 Edge Concrete Blocks On site 0.00
500 sq feet Erosion Control Blanket CS3 Western Excelsior 170.00
1 Sprinkler System Home Depot 60.00
Total Cost $420


Instructions for Implementation and Use After installation, more plants will need to be added to the roof. These can be added by carefully planting on the roof, or by spreading seeds under the erosion control blanket. Extra heavy watering will be needed initially to get the plants established.

Periodic Watering When the plants on the roof look wilted or there has not been any substantial rainfall, the roof will need to be watered. This can be done by turning on the spigot on the north side of the building, two feet of the ground. Water should occur no more than twice a week, and for only twenty minutes.

Yearly Cleaning The maintenance of the green roof will require occasional pulling of weeds, cleaning of drain gutter, and inspecting of the sprinkler heads. Quarterly flushing will require approximately one to two hours.

Safety Precautions As the blocks on the side of the roof are not attached to anything, great care should be taken when accessing the roof. A 12 foot or higher ladder is recommended.

next steps

We are looking forward to building the roof!