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Living Roof Materials

I want to install a living roof on my home, and already had the waterproof membrane installed by a roofer. But I've had trouble finding a source for the other components, such as filter layers, planting media, and plants. Please help!

Hal Craddock • Lynchburg, Virginia

Living (also called "green") roofs can improve your home's energy efficiency by providing additional insulation, and can reduce your home's environmental impact by using and slowing rainwater runoff instead of it flowing across impervious surfaces to ultimately end up in storm drains. However, these roofs have strict waterproofing, drainage, and structural requirements that are best addressed by professional designers or contractors. Therefore, make sure that your roof structure is engineered to local building codes and capable of supporting the green roof's added weight. Also, be sure that you have obtained the proper permits and are confident that the membrane has been properly installed before you begin adding layers.

When shopping for the nonliving roof components, start with manufacturers that are members of Green Roofs for Healthy Cities ( Another good resource for environmentally preferable products is BuildingGreen's GreenSpec online directory (, which features listings for living roof systems, components, planting media, and plants.

While I suspect most of the living components would be available to you locally, consult with a landscape architect or living roof contractor before you make your purchases—your plant choices depend on much more than your roof's microclimate. The roof's slope, load capacity, media composition, and, ultimately, maintenance requirements are just a few of the factors that the experts can help you consider to select appropriate vegetation.

Mick Dahlberg • Solar Energy International

Living roofs are especially attractive for the home heating and cooling savings they can offer.

Solar Combo?

It is well known that photovoltaic (PV) module output suffers when the modules get hot. Has anyone ever suggested trying to cool them with a coolant loop? Why aren't PV modules made with the capability to be cooled—sun on one side; coolant on the other? I know it would take energy to move the coolant, but it seems like it wouldn't take much. Or maybe convection could circulate the coolant, eliminating the need for a pump entirely.

Woody Ligon • Farmville, Virginia

Not only has the suggestion been made, but it usually is taken one step further to include using the heated water for domestic purposes. At least one company—Dawn Solar Systems—has developed a system that circulates water through PEX tubing behind PV shingles to remove heat from the roofing and preheat domestic water. But this is a specific case of PV shingles, which lack air circulation and are prone to high temperatures.

This idea has not been adopted for other types of PV modules for these reasons, some of which also apply to your proposed PV module cooling idea:

• Electricity and electrical components should not come in contact with water since electrical shorts and harmful oxidation may occur.

• Combining electricity production and water heating in one unit doubles the system complexity. When one or the other fails, you're faced with replacing a more expensive unit.

• Solar hot water collectors rely on a high heat differential between the incoming water and collector temperature to be effective, but PV modules should not be allowed to reach these temperatures.

Lots of folks have experimented with this idea, but the experimenters and the market have so far concluded that the extra complexity and cost are not worth the minimal energy gains. For my investment, I'll stick with separate, relatively simple, purpose-made systems.

Michael Welch • Home Power

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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