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Lesson: Green Roof Design

(Lesson courtesy of Science NetLinks) Level: Grades 9-12.

Lesson_Plan_GreenRoof2

Chicago’s City Hall Building

Summary

In this lesson for grades 9-12, students work in teams to design a heat- and water-conserving “green roof” of plant material for an urban apartment building. They address economic and community considerations of green roof design.

Objectives

Students will:

  • Study design decisions that affect energy transfer between a building and the outside environment.
  • Identify and consider decisions involved in improving a building’s energy profile.
  • Analyze economic and community aspects of green roof options.

Overview

Students work in small teams to design a heat- and water-conserving “green roof” of plant material for an urban apartment building. This multimedia project involves Web and library research, hand drawings, creation of exhibit boards with text, photos and data graphics, and a final presentation of findings. It is based on authentic processes that professional engineers perform to win green roof clients. The  students will be required to submit a response to the green roof “Request for Proposal” (RFP) described below, in the Development section.

When finished, student teams present their plans to the class/school (via front-of-the-room conference format or “Science Fair” exhibits with students evaluating each other’s boards).

For  assessment, the teacher will work with the class to devise a rubric for evaluating the proposals. To use it, each student should write a summary of two different presentations, noting how each met the rubric requirements.

In executing this project, students will develop an understanding of the basics of green roof design as an energy management system—not just an architectural or ideological construct.

National Science Education Standards:

  • Science and Technology: Abilities of Technological Design (9-12) #1, 2, 3, 4, 5
  • Physical Science: Conservation of Energy and Increase in Disorder (9-12) #4

Previous Knowledge

Before undertaking this lesson, students should have sufficient literacy skills to extract and synthesize meaningful concepts and data from written Web materials, and to construct a written argument citing evidence from multiple sources. They also need the analytical and discernment skills to evaluate evidence as text, images, schematics, and data graphics. In terms of group work, they need the maturity to work collaboratively in small groups, and to be active, contributing members to the creation of the final product and its presentation.

Research suggests that middle- and high-school students don’t always regard heat exchange as an interaction. To overcome this misconception, teachers can work through the Addressing Misconceptions about the Transfer of Energy sheet with students—either as a “thought” experiment, or a physical exercise using a bucket of ice cubes and a thick mitten.

Materials

  • Access to computers with Internet connection
  • Graph paper
  • Colored pencils for sketches and rendering
  • 3-ring binder for consolidating each team’s responses to the RFP, to include 2 pages of written text; map of project which they draw, and 1 data graphic they create expressing quantitative relationships such as current energy conditions of the building, and projected savings due to the green roof. These may be augmented with PowerPoint presentations, flip charts, or poster boards for the presentation.
  • Designing a Green Roof Solution student E-sheet
  • Action Step for Designing a Green Roof Solution student sheet
  • Addressing Misconceptions about the Transfer of Energy teacher sheet

Background

A green roof is generally a flat roof of a building that is planted with a variety of plant life and is therefore green in color. It might look like a rooftop garden. In Germany, an estimated 10% of the buildings incorporate green roof technology. Though certainly pleasing to the eye, green roofs attract attention for other reasons now in the U.S.

Green_Roof

Green Roof at Vendée Historial, les Lucs sur-Boulogne, France

Three main reasons for the emerging interest in green roofs are:
1. The biomass of the plants slows the transfer of heat from the environment to the interior of the building, thus serving to insulate and conserve heat—which is a major financial concern in this era of energy crises.

2. The green plant coverings also help maintain water quality by absorbing 60% to 100% of the rain that falls on them. This reduces storm water runoff that contributes to pollution by washing contaminants off building roofs into water systems. Storm water can be a cause of erosion or flooding when fast-flowing water leaves an uncovered roof and is shunted over a soil bank or into a storm sewer system.

3. Green roofs conserve building materials by protecting the roof from the effects of weathering and harsh sun, or repeated freeze/thaw cycles that can crack roof coverings and require them to be repaired or replaced more frequently than roofs protected by plants.

To see an example of a green roof project created by college students, look at Macalester College’s First Green Roof, a project designed by college students in St. Paul, Minnesota with the help of a $10,000 grant won from the U.S. Environmental Protection Agency in an energy conservation contest. The engineering specifics of this project can be found here. For a detailed photographic and text report by the students of the creation of the green roof, visit Macalester College’s First Green Roof (.PDF).

Reviewing the Background Material

Once you have gone over the background material  with students, test their understanding and comprehension with the following discussion questions:

1. There are at least three types of green roofing systems commonly built. Name or describe them, and list a key feature about each.

Answer: An intensive green roofing system has higher costs, maintenance, and structural needs, but provides more public access, biodiversity, and creates more habitat. An extensive green roofing system needs less growing medium, is light weight, is well suited to prairie grasses, and low maintenance. A containerized green roofing system is inexpensive, very light weight, low weight, and uses low-growing plants.

2. Which kind did of green roof did Macalester choose, and why?

Answer: It chose a containerized green roof because it was the least expensive, required the least maintenance [needing water 2x/week], only required light weeding, and little building inspection so it needed little input from Macalester staff.

3. The Macalester green roof is a kind of living laboratory. They want to collect data from it. What kinds of information can they get by monitoring their green roof—and by what means?

Answer: 1. The insulation value of a green roof by comparing building heating and cooling expenses before the green roof and after it. 2. Membrane durability/lifespan by inspecting the same roof components regularly and recording their status against desirable performance standards. 3. Water quality by testing for acidity and particulate load in catchment containers, and in soil moisture. 4. Water runoff by extrapolating from rain gauge measurements over the square footage planted.

4. What are some of the benefits commonly associated with green roofs in general?

Answer: They slow runoff, ease urban heat island effect, increase building insulation, and add beauty.

5. Name three steps the student group took to make the project appealing to the granting agency so they could win the $10,000.

Answer: 1. Talked with college building managers to get permission 2. Researched suppliers to make a list of people whom they called and interviewed so they could draft a realistic budget and identify future funding partners for materials/plants/money 3. Networked with other green roof community groups to show community involvement.

6. In her description of creating the project, name some of the skills Alese said she learned from creating a green roof.

Answer: The skills include community organizing; project management; scientific research methods; responsible, collaborative environmental activism; and communication in letters and in making oral presentations.

Procedure

Note: If a guest speaker can be engaged to visit the classroom — or a fieldtrip arranged — the authenticity of the exercise would be greatly enhanced.

Tell the students that they are assigned to design a green roof for an urban apartment building in New York City. They will work in collaborative teams and research the topic through Internet and library resources, then write and illustrate a short report to present their design. Their design will mimic the real-world engineering process in which engineers submit a design in response to a Request for Proposal (RFP). The design requirements for the RFP are outlined in the Action Step for Designing a Green Roof Solution student sheet.

In their RFP, students should incorporate what they’ve learned about green roof technology, urban heat islands, and managing heat transfer through green roofs. They will propose a solution to a heat transfer problem in an urban building in words, pictures, and data graphics.

Before students begin the project, they should add to their knowledge about green roofs by using their Designing a Green Roof Solution student E-Sheet to go to and read Green Roofs. Once students have had a chance to look at this resource, pose these discussion questions:

1. What motivated Europeans to be leaders in green roof technology? Why are Americans slower to adapt? Answer: Energy costs are higher in Europe and they have a more deeply engrained cultural tradition to conserve resources. As energy costs rise in the U.S., green roof technology is more appealing and more businesses that supply materials have arisen to meet those needs.

2. If we think of the green roof as a “sandwich,” what are the three layers? Answer: The bottom is a vapor barrier; middle is soil/gravel/growing medium; top consists of plant modules that lock into place, like tiles.

3. Now that we know the three layers, explain the role of each. Answer: The bottom is a vapor barrier to seal/slow heat transfer from the building to the outside; middle is soil/gravel/growing medium that supports plants, contains water to prevent runoff, and the top consists of plant modules that lock into place, like tiles. Plants absorb outside heat to slow transfer and conduct water into soil to slow/prevent storm runoff.

4. What data did the Pennsylvania researchers have to suggest to them the green roof might help manage heat transfer? What would be a next good step to complete the experiment that measures green roof success? Answer: Temperature probes on a summer 90º F. day on the bare roof measured 145º F; on the roof gravel 119º F. and on the plants 82º F., indicating a progressively cooler environment achieved by the addition of green roof materials.

Next,  students should study the concept of the urban heat islands. Urban heat islands increase energy costs of maintaining buildings, and are a problem students will address in their green roof design. To do so, they can use their student E-Sheet to visit:

The Making (and Breaking) of an Urban Heat Island

Beating the Heat in the World’s Big Cities

Once they’ve looked at these images and read the Web story, they should answer these questions:

1. What conclusions can you draw from a comparison of the two enlarged Landsat images of New York City? Answer: Where vegetation is dense, temperatures are cooler. Urban heat islands are worst where there is little or no vegetation.

2. The color distribution of this image correlates with temperature variance in New York City. Where does it look the hottest? Answers will vary.

3. What areas look the coolest? Answers will vary.

4. To what do you attribute the difference? Answers will vary.

5. What general principles about urban heat islands does it suggest? Construct a hypothesis about energy interactions and transfers. Answers will vary.

6. What information is NOT on this graphic that would be helpful in making a scientific summary of the problem? Answer: A key noting time of day, a scale in miles and kilometers for international audiences, and date all would be helpful for extracting the most meaning from this image.

Now go over the green roof design project with students on the Action Step for Designing a Green Roof Solution student sheet. Students should follow the directions on this sheet to help them develop their RFP that proposes a green roof solution for an urban building. They should describe it in words, pictures, and data graphics.

Assessment

For the assessment, students should work with you to design a written rubric of selection criteria they think the building owners should use to help select a design plan.

Once the rubric is decided and written, students have a chance to revise their presentations so they more closely conform to it.

Each team then presents its plan to the class either serially, in a front-of-the-room conference format, or simultaneously in a “Science Fair” exhibit setting through which students walk to evaluate the boards.

Assessment requires each student to write down a summary of at least two different presentations and hand it in to you. They must evaluate them against the rubric the class devised for the use of the building owner in the selection process.

For your own assessment purposes, you are to evaluate their presentations on how well they address foundational concepts of the Benchmarks.

Extensions

  • Plan a field trip to a local university/college/arboretum that has a design/horticulture/environmental science library to examine books and journals on the topic there. Ask for a tour of topical subjects in the library and labs from graduate students and professors.
  • Now that your students have a solid understanding of the energy management issues that green roofs can address, and the design decisions and the social context in which all this happens, arrange a field trip to green roof building to talk with the planners about their experience. If you can’t visit the site, arrange a webinar, or even a conference call broadcast on speaker phone with an exchange of site photos. Email your sources a list of three questions before hand to focus the discussion. Macalester College students are happy to help. Here are some sample questions:

1. In your Green roof project, what were the driving forces—would you characterize them as mainly budgetary? As fulfilling the institution’s environmental ethic? Was it political, and how/how not? Were they marketing to attract environmentally aware students and professors to your college? Other motivations?

2. Is there a standard cost/square foot? What was it in your area?

3. How will you measure the success of your green roof in meeting its varied goals?

4. If you could tell people one thing to DEFINITELY do in embarking on a green roof project, what is it, and why? What is the one thing to DEFINITELY NOT DO, and why?

  • Highly motivated students can seek out other sites/data to map regional costs or density of green roof projects. By conferencing with green roof creators in different parts of the U.S. (or world), students can explore the latitudinal effect of heat distribution in green roofs, map the results, mine satellite images, and Google Earth for data. Highly motivated students can seek out other sites/data to map regional costs or density of green roof projects.

3 Responses to “Lesson: Green Roof Design”

  1. [...] Teachers interested in introducing the creation or classroom study of green roofs might start by exploring the American Society of Landscape Architects’ (ASLA) teacher guide and student workbook. Take a look, as well, at our eGFI green roof lesson plan. [...]

  2. [...] eGFI Teachers’ Green Roof Design [...]

  3. [...] eGFI Teachers’ Green Roof Design [...]

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