What a Green Roof Is
A green roof is a special roofing system covered with a waterproof layer, soil, and living plants. The concept actually dates back to ancient times like the Hanging Gardens of Babylon. The modern English term became popular in the 1970s when builders started designing environmentally friendly houses. Today, it is a great way to make your home look unique and help the environment.
Building a green roof takes several layers. You cannot just put dirt on top of your house. Builders start with a thick waterproof membrane to keep water out of your living room. Next, they add a root barrier so plants do not grow into the wood. Then comes a drainage layer to let extra water escape. Finally, they add a special lightweight soil and the plants.
Why It Matters to You
A green roof acts like a thick blanket for your house. In the summer, the plants and soil soak up the hot sun. This keeps your roof cool and stops heat from baking the rooms upstairs. Because your house stays cooler, your air conditioner does not have to work as hard. You can learn more about managing your home temperature in our guide to HVAC & Climate Control.
These roofs also handle heavy rain very well. Normally, rain hits your shingles and rushes straight into your gutters. This fast water can wash away your yard or flood your basement. A green roof acts like a giant sponge. The soil soaks up the rain and releases it slowly. This takes the pressure off your gutters and helps protect your property.
Where You Run Into It
You will mostly see green roofs on flat roofs or roofs with a very low slope. Steep roofs make it too hard to keep the soil from sliding off. Many homeowners build a green roof over a garage, a backyard shed, or a flat home addition. You might also hear contractors call it a living roof or an eco roof.
There are two main types of green roofs you will encounter. Extensive green roofs have a thin layer of soil. They usually grow small plants like moss or sedum. These plants survive tough weather and need very little care. Intensive green roofs have deep soil. They look like a real garden with bushes and sometimes even small trees. These require a lot more maintenance and a much stronger building underneath.
What to Watch Out For
Wet soil is incredibly heavy. Never try to build a green roof without hiring a structural engineer first. If your roof frame is too weak, the entire roof could collapse into your house.
Weight is the biggest challenge. A standard roof is built to hold shingles and maybe some snow. A green roof adds hundreds or thousands of pounds of wet dirt. You will likely need a contractor to add extra wood or steel to your framing. You can read more about how your roof is built in our Roofing guide.
You also have to remember that a green roof is a living thing. It is not like regular shingles that you can just forget about. You will need to pull weeds that blow up there. During long dry spells, you might even have to climb up and water the plants so they do not die.
What It Costs
Installing a green roof is a major investment. A basic extensive green roof usually costs 15 to 30 dollars per square foot. If you want an intensive roof with deep soil and larger plants, expect to pay 30 to 50 dollars per square foot. Keep in mind that these ranges vary based on your location and the specific plants you choose.
You must also budget for the prep work. Hiring a structural engineer to check your home will cost 500 to 1000 dollars. If they say your roof needs more support, reinforcing the wood can easily add 2000 to 5000 dollars to your total bill.
