Ask the Green Architect: The Skinny on Green Roofs; Retiring Your Refrigerator; Earthen Floors

Ask the Green Architect: The Skinny on Green Roofs; Retiring Your Refrigerator; Earthen Floors

Green architect Eric Corey Freed answers your questions on sustainable building performance, materials, and design.

  • The Skinny on Green Roofs
  • Retiring Your Refrigerator
  • Earthen Floors

    How does a green roof work? What are the benefits and drawbacks?

    Not only do green roofs protect your roof membrane, they also add insulation and beauty to your roof.

    Green roofs are not recommended for a roof area that is not seen, as there are easier ways to get an efficient roof. But for a roof with visibility, such below an apartment building or office, a green roof will enhance and beautify the surroundings, all while purifying the water, cleaning the air and insulating the roof.

    A green roof system is an extension of the existing roof, and not potted plants as many assume. The system consists of a special water proof and root repellant membrane, a drainage system, filter cloth, a lightweight growing medium and plants on top.

    Green roof systems may also be modular, with the drainage layers, filter cloth, growing media and plants already prepared in movable, interlocking grids or trays. These are good for areas where access could be an issue.

    In North America, the benefits of green roof technologies are poorly understood, despite the efforts of several industry leaders. In Europe however, these technologies have become very well established. Cities like Chicago have launched a Green Roof Initiative, serving as a model for other cities.

    Before you initiate a green roof installation, you will need to know the slope, the structural loading capacity, and existing materials of the roof, as well as the nature of any drainage systems, waterproofing, and electrical and water supply in place. You should also consider who would have access to it, who will do maintenance, and what kind of sun and wind exposure the roof gets.

    Plant selection depends on a variety of factors, including climate, type and depth of growing medium, loading capacity, height and slope of the roof, maintenance expectations, and the presence or absence of an irrigation system. A landscape architect would be able to advise you on suitable plants and design of the plantings. (See the landscape contacts below.) Here in California, Rana Creek is the leader in green roof systems and design.

    The cost of a green roof varies considerably depending on the type and design factors. As a budgetary figure, a green roof may be installed for $12.00-$24.00 per square foot. While this might seem expensive, it also reduces the need for additional insulation, and protects the real roof below it.

    The biggest obstacle in adding green roofs to smaller projects is the added weight they create. As a rule of thumb, a green roof weighs the same as water, about 60 pounds per cubic foot. The additional weight might require additional roof structure, and therefore, additional cost.

    A final issue to consider in looking at a green roof system is how other functions like photovoltaic solar panels could make better use of a particular roof space.

    When installed, green roofs provide a beautiful and environmental alternative to traditional roofing. By knowing the considerations, you will be able to choose an appropriate solution.

    Further Reading:

    Green Roofs: Ecological Design and Construction

    California Department of General Services Quick-Response Studies Guide (PDF)

    Architectural Group to Install Green Roof at D.C. Headquarters

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Instead of operating a refrigerator during the cold months is there a way to harness the cold outside air to keep the food cold?

The U.S. Department of Energy (DOE) says that every appliance has two price tags: a purchasing price and an operating cost. In any home, the refrigerator is typically the largest consumer of electricity. The idea of using the cold air outside makes so much sense; one has to ask why it is not done.

Well, actually, it was done for centuries in the form of root cellars. Root cellars are nature's way of storing fruits and vegetables, acting as ideal storage areas for anything you wish to keep cool. Typically used for vegetables (roots like potatoes), but also for meat, milk and fruit.

Although root cellars do not get as cold as a refrigerator during summer months, root cellars generally are 30 to 40 degrees F cooler from daytime summer temperatures. Similar to the principles of a wine cellar, the mass of the earth maintains a cooler temperature below ground. An insulated door covers a 6' by 10' hole in the ground, with stairs down to the storage.

It is also worth noting the wonderfully energy efficient units from SunFrost. Sun Frost makes the world's most energy efficient domestic refrigerators and freezers. The efficiency of their refrigerators make them ideal for use with solar power, or anywhere you are generating your own power.

If the SunFrost seems out of your range, at least consider an Energy Star-rated appliance to save as much energy as possible. A new refrigerator with an EnergyStar label will save between $35 and $70 a year.

The reason refrigerators are such energy hogs is mostly due to inefficiency. Look at this great article listing numerous ways to reduce your existing fridge's energy use. Here is a sampling of some good practices:

Operation Practices:
  • Minimize frequency/duration of open door
  • Check the door gasket
  • Don't overload the refrigerator
  • Correctly set the dial thermostat
  • Re-examine refrigerator's contents weekly
  • Evaluate the refrigerator's size
  • Maintain clearance around refrigerator
  • Design alcoves properly
  • Consider alternative refrigerator sites
Design Changes:
  • Trade in frost-free units
  • Insulate the refrigerator
  • Re-locate the HDC (heat-dissipating coils)
  • Build a hybrid refrigerator/water heater
  • Use a horizontal refrigerator
I'm considering an earthen floor with radiant heating, in a new strawbale house. Have you installed these, and seen that they last and don't crack (much) over the years? I'd like to know if it's a good, long-term investment, especially with the radiant heat.

Technically, a true modern day earthen floor comes in various mixtures. Some are a mix of cement and earth (as in rammed earth construction). The earth chosen makes a large difference in the durability. For instance, the more clay content, the more susceptible it is to cracking from changes in water content (the clay expands and contracts quite a bit).

If you are purchasing commercial grade soils for this floor, you can select a "plasticity index" but most single family houses just collect soil leftover from the excavation for the house. The correct soil will stabilize and prevent cracking, but there are no guarantees.

Be sure to seal the floor when complete. The best sealer I have found is simply boiled linseed oil, thinned with turpentine and brushed on in several coats. (The odor will be gone in a week.)

This system is the perfect complement for radiant heat. The thermal mass of the earth will store up the heat and maintain a nice, consistent temperature all winter long. You could also use the same system for radiant cooling, by running cool water through the same tubes.

Further Reading:

Pacific Domes -- Earthen (Cob) Floors

Green Buildings Materials Guide -- Earthen Flooring

Cob & Earth Building

Alternative Construction: Contemporary Natural Building Methods

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Eric Corey Freed is principal of organicARCHITECT and teaches sustainable design at the Academy of Art University in San Francisco and University of California Berkeley. He is on the boards of Architects, Designers & Planners for Social Responsibility (ADPSR), Green Home Guide, and West Coast Green.