What's the least expensive way to green your roof?

To determine the best way to green your roof, first think about your roofing needs and what you hope to accomplish. Do you want to generate electricity, control runoff, or just cool things down? Are you replacing an old roof, building a brand new home, or hoping to improve the performance of an existing roof without removing or replacing it? What sort of climate do you live in? Are you more concerned with staying warm in the winter, cool in the summer, or both? And, last but not least, how much are you willing and able to spend? Are you prepared to spend more up-front for potential long-term returns, or do you want to do whatever you can with very limited financial resources?

If you live in a hot climate and your primary objective is to lower your cooling costs, a cool roof is a less expensive alternative to a green roof. A cool roof reduces the surface temperature of your roof, lowering the temperature inside your home. If your roof is currently black or another dark color, consider cooling it off by coating or shingling it in a light color. If you have a flat or barely sloped roof, you can have it recoated in white for 75 cents to $1.50 per square foot [source: Environmental Protection Agency]. If your roof is steep, you can replace your standard shingles with a "cool pigment" shingle for anywhere from 60 cents to $2.10 per square foot [source: Environmental Protection Agency].

If money is no object and reducing your carbon footprint is your top priority, alternative energy technologies such as solar panels and wind turbines can use your roof's exposure to sun and wind to generate some or all of your household electricity. But their high price tag (from around $3,000 for a small 1-kilowatt residential wind turbine to upwards of $33,000 for a solar array to provide all the electricity for an average home) means that it will take years to recoup your initial investment [source: Windustry].

Even if a green roof, cool roof, or solar array isn't in your budget, there are ways to put the surface of your roof to work for you. These super-affordable options won't reduce temperatures on your roof or solve global warming, but they can help you cut your utility bills and reduce your environmental impact. Read on to see if one is right for you!

If you can't afford a truly green roof, here are some other ways to reduce energy consumption.

Add a skylight If you find yourself turning lights on during the day to brighten dark rooms, let the sun shine in with a traditional skylight or a solar tube skylight.

A solar tube skylight is a reflective metal tube with a lens at the top that directs sunlight from the roof to the inside of the house. Ranging in diameter from 10 to 22 inches (25 to 55 centimeters), solar tubes can brighten up to 600 square feet (55 square meters) of living space [source: Griepentrog]. With an average cost of about $500 installed [source: DIYornot], tubular skylights are an affordable way to brighten your home and reduce your energy consumption.

Traditional skylights are more expensive to install, with estimates ranging from $600 to upwards of $1500, depending on the size and type, but Energy Star-rated models may be eligible for tax credits [source: Environmental Protection Agency].

Build a rain barrel If your funds are limited but your DIY skills are up to par, you can help to conserve water and reduce stormwater runoff by collecting the rainwater that streams off your roof in one or more rain barrels. Rain barrels can be found online or in some hardware and home and garden stores for around $100, or you can make one yourself with a salvaged plastic barrel and some basic plumbing fixtures.

Installing a rain barrel won't do anything to cool your roof, but the water you collect can be used to water your lawn and garden, and diverting the overflow from your downspouts before it hits the ground helps to keep pollution out of streams -- as worthy a green endeavor as any!

The bottom line is that there's no one "best" solution that works for every situation. While a green roof is the most expensive up front, it does provide long-term savings and quality of life benefits, especially if you live in a city where grass is a rarity. Whether you choose a green roof, a cool roof, solar panels or skylights, your lifetime costs and savings will vary depending on the size and type of your roof, your heating and cooling needs, and the location and situation of your home.

And if you still have your heart set on a rooftop garden, don't give up hope: there's some evidence that costs may go down as the technology becomes more widespread. In Germany, where green roofs are much more popular than they are here, their cost ranges from 8 to 15 dollars per square foot [source: Environmental Protection Agency.] It's still not cheap, but it's a start!