How much does it cost to install green roof?

Known as living roofs, eco-roofs, and vegetated roofs, green roofs offer many benefits to the user. The process of growing living plants on the roof of a home or building has been shown to dramatically decrease cooling costs for the building while enhancing stormwater management and air quality for the area. It also adds a beautiful look to the space, with plants replacing traditional roofing shingles or tiles. Some install them for cooling purposes, while others do so for stormwater management in dry climates. In any case, proper installation of a green roof is best done by a professional.

The national average cost for green roofs ranges from $15,000 to $30,000. Most homeowners spend about $22,000 to create an extensive built-in green roof covering 1,500 sq.ft. At the low end, you may be able to get modular green roofing installed on a smaller 1,000 sq.ft. roof for around $12,000 with basic design elements and moderately priced plants. While at the high end of the spectrum, you could spend as much as $70,000 on premium green roof design, irrigation, premium plants, and installation for a 2,000+ sq.ft. roof.

Green Roof Price

What Is a Green Roof Made Of?

A green roof is made up of a layer of materials, starting with the structural roof support on the bottom, then the vapor control layer and thermal insulation. This protects the roof and the plants alike, along with the roofing membrane that is added after the insulation. Then, there is a green roof root barrier and waterproof barrier put into place, followed by the drainage, a filter, the soil or growing medium, and then the vegetation. These layers work together to create an ecosystem that supports green roofing while protecting the actual roof material underneath.

Green Roof Costs per Square Foot

You can expect to spend $10 to $35 per sq.ft. on green roof installation, depending on the type of green roof you choose and what kind of plant coverage you select. Most jobs are priced by the square foot, but there may also be additional charges for design, extra labor that goes above and beyond the “typical” process, and so forth. Usually, you will spend less per sq.ft., and in total, for a more basic green roof than an upgraded biosolar roof, for example. For roofs over 10,000 sq.ft., the cost per sq.ft. could be discounted as much as 50% of what is listed here.

Green Roof Installation Cost by Type

You will spend between $10 and $35 per sq.ft. on your green roof based on its type. There are five types of roofing to choose from in this category, each with its considerations, plants, and designs to consider. Each type of green roof features its own plants and design principles, which affect the total cost you pay. In the table and subsections below, you will see an example of how much you will spend on your green roof based on the type that you choose.

Extensive Green Roof

An extensive green roof is the most common and least expensive type of green roof, with costs ranging from $10 to $20 a sq.ft. They consist of a thin layer of soil with continuous coverage of growing material. They are fairly lightweight and can be installed on roofs with a pitch from 0º to 30º. They are virtually maintenance-free once set up and do not require irrigation. The plants and greenery on these roofs offer the best value for the money.

Semi-Intensive Green Roof

For this type of roof, costs range from $15 to $30 per sq.ft. A semi-intensive roof is often referred to as a rooftop garden. It is heavier than an extensive roof and usually has plants in modular containers rather than free-growing. When constructed on a concrete roof, visitors can walk around the growing medium. They require more care, maintenance, and irrigation but can provide a more sculpted appearance.

Intensive Green Roof

Intensive roofs are the most expensive, ranging from $25 to $35 per sq.ft. They are very heavy, with a thick layer of soil. They allow the most customization for the rooftop. However, they must be installed on a flat, concrete roof and require a lot of care, maintenance, and irrigation. These are not normally practical for residential buildings but can produce dramatic and beautiful results. Because of the maintenance and other requirements of this type of roof, it is best on commercial buildings with a dedicated care staff.

Blue-Green Roof

These roofs have an average cost of $25 to $35 per sq.ft. The blue-green roof is designed for city usage in areas with heavy rainfall that need rain storage and management. They combine rain storage techniques with green roof technology, so they have fewer plant options. They require a flat, concrete roof that can bear the weight. You will not see these on residential roofs with steep pitches or that cannot bear much weight.

Biosolar Roof

Biosolar roofs have two components: the green roof portion, which costs between $25 to $35 a sq.ft. and the solar panels, which cost an additional $250 to $600 per panel. A biosolar roof is a green roof with solar panels installed, offering dual benefits for energy savings. It may be intensive or semi-intensive and usually has modular growing mediums rather than complete coverage. They are not normally installed on residential roofs due to their weight.

Green Roof System Cost by Type

The cost of a green roof system ranges from $10 to $35 per sq.ft. Depending on the type, people pay more for a built-in or custom-designed roof and less for modular or roof tray systems. Several factors affect the decision as to which type of roof to install. For example, the pitch of the roof and the design ideas you have in mind will determine whether prefabricated green roof trays are a better choice than built-ins. In the table and subsections below, you will see a cost breakdown of each, along with their most important factors to consider.

Modular Green Roof System

The average modular or green roof tray system cost is between $10 and $30 per sq.ft., slightly less than built-in roofing, which requires more customized designs and more onsite work. Additional labor may be involved in getting all the materials to the roof, but modular roofing is quick and easy to install. You can find tray systems that include all kinds of hardy plants and greenery that are perfect for green roofing and easy to put in place. The modular system allows pre-built trays to be brought to the roof and installed, ready to go with plants in place. It is quicker than built-in systems but has cost and weight considerations.

Built-In System

If you choose a built-in green roof, you will spend closer to $20 to $35 per sq.ft., depending on the complexity of the design and installation of your custom-built green roof. Built-in systems are lighter and easier to install on roofs with standard plywood decks, while it’s best to leave modular systems for concrete roofs. These built-in green roofs are also great for roofs with a steeper pitch and those needing a more custom design. A built-in system is one that is constructed and seeded on-site, as opposed to modular roofing that brings in ready-to-install trays. That allows the built-in roofing to fit the exact design, pitch, and other factors of the roof for a more customized result.

Green Roof Construction Cost

For a 1,500 sq.ft. roof, expect the labor portion to make up roughly $7,500 of the $15,000 total. Labor makes up a significant portion of the cost of a green roof, mostly because the process of creating one can be labor-intensive and is done by a certified Green Roof Professional (GRP). Getting the materials onto the roof, constructing the layers, and installing the plants is extremely time-consuming and can cost $5 to $10 per sq.ft. in labor.

Roofs with a steeper pitch or those with intricately designed patterns for growing cost significantly more than roofs with seeds mixed into the growing medium prior to installation. Green roofs are essentially built up or installed in layers. Every installation should start with an assessment from a structural engineer to determine how much the roof can hold per foot. Not every roof is a good candidate. Some roofs require substantial work before installing a green roof.

A roof barrier, usually a type of heavy plastic, is spread over the roof to ensure that the roots do not penetrate the roof deck. If the roof has walls or there will be walking paths, these are lined with gravel. Then, the moisture retention layer is placed, which looks similar to egg crating. A filter fabric goes on top of this, which is what holds the growing media or soil. Soil is placed on the filter fabric, and the plants are installed. This may be done through seeds, planting seedlings and small plants, or installing trays of ready-grown plant material. Installation takes roughly 5 to 7 days. However, it will take several weeks for the plants to establish themselves.

Plants

Plants for a green roof vary depending on the area where you live and your climate. Like plants that grow in the ground, the plants for your green roof do best if they grow well in your climate. Wildflowers and sedum do best, but you can plant grasses and various other plants. The better choices include aromatic herbs, clover, groundcover, and succulents. For an extensive green roof, the plants should be able to grow in under 5 inches of soil. Plants for an intensive green roof may be able to have a deeper root system because there is more soil for the plants to take root. Grasses, for example, will do well on intensive green roofs but not so well in shallower soil.

Other factors that determine the types of plants include irrigation and the purpose of the roof (energy conservation, stormwater management, heat reduction, etc.). A semi-intensive green roof gives you the option to grow both shallow-root and deeper-rooted plants. As green roofs expand to urban areas, agriculture is becoming popular with these roofing systems, allowing anyone to harvest fresh crops, even in the middle of the city. You can plant tomatoes, cucumbers, salad greens, and other foods in addition to the plants and grasses discussed.

Irrigation System

Extensive green roofs, which are most often used for residential homes, do not require watering. However, semi-intensive and intensive roofs do. In most cases, you need an irrigation system designed into the roof itself, both for drainage and to allow for proper irrigation and spread so that all plants receive the correct amount of water. Also, you do not want any large puddles of water. This can be done through tubing as well as by using water-storing mats. It is also important to note that many green roofs rely on plants like succulents because they store water and do not require as much irrigation. So, natural rainfall may be all that is needed.

Benefits

Green roofs have numerous benefits for the user. They have been shown to reduce cooling costs for buildings by as much as 25%. They also help manage stormwater runoff in areas with a lot of rainfall and can improve air quality when installed in urban environments or on large, city-wide scales. Green roofs are also attractive, and some can be very low-maintenance, extending the lifespan of the roof itself. Most homes can benefit from a green roof, whether from green building certification to the aesthetics of a rooftop garden.

However, the setup costs for a green roof are high. They are expensive, and more intensive green roofs can only be created on concrete roof decks that can handle their extreme weight. While many people like the idea of a rooftop garden, it is not easy or possible to achieve in most residential settings. In the winter months, a green or living roof may not look as attractive because the plants may not be evergreen. Intensive green roofs set up on commercial buildings also require a lot of maintenance and irrigation to help them stay their best.

Pitch

The pitch of your roof dictates, in part, which type of green roof system you can use and whether you can install a green roof system at all. Intensive green roofs must be installed on concrete roofs that have 0º pitch. Extensive green roofs can be installed on roofs with a pitch up to 30º but preferably less than 20º. The closer to flat the roof is, the easier time you will have installing the growing medium and plants.

Green Roof Maintenance Costs

For an extensive roof, expect to pay $0.75 to $1 per sq.ft. in maintenance costs each year. For an intensive roof, annual maintenance costs range from $1 to $1.50 per sq.ft. The maintenance your green roof requires depends on the type of roof and plants you install. An extensive roof that is well-established does not require a lot of ongoing maintenance. You may want to fertilize it occasionally or water it in times of drought. Otherwise, extensive roofs are relatively self-sustaining.

Intensive roofs, however, need more work. If you have a rooftop garden, it may require the same level 5 of care as any decorative garden bed. You also need to irrigate regularly and check to ensure the drainage systems operate properly. Your roof should be inspected regularly to make sure that it holds the weight of the green roof properly with no moisture problems or leaks.

Cost of Green Roof vs Conventional Roof

Compared to the average $15,000 to $30,000 spent on green roofs, conventional roofs will average between $7,000 and $24,000, depending on the size, type, and features. When comparing the costs of green roofs and conventional roofs, it is important to look at both the short-term and long-term costs. In the short term, green roofs are more expensive than conventional roofs because the installation and material costs are higher overall. However, in the long term, having a green roof can actually save you money compared to a conventional roof.

A green roof provides insulation to the home, reducing the energy needs and thereby lowering the amount of money you spend on utility bills during the year. Not only that, but a green roof also protects the roof structure from things like the sun, rain, and snow, extending the lifespan of your roof and minimizing the amount of repairs that need to be done. General maintenance costs are also lower for green roofs than conventional roofs, and studies have shown that green roofs can save home and building owners thousands in the long term when compared to conventional roofs. The table below shows a breakdown of the costs of each type of roof.

Enhancement and Improvement Costs

Roofing Inspection

Roofing inspections cost from $100 to $600, depending on the size and level of inspection. Unless you have a new roof installed to support a green roof, your existing roof should be inspected prior to installation. You can put a green roof on an existing roof or building, but it needs to be inspected first to make sure it can handle the weight. Many cities and municipalities have laws about proper codes and building capabilities. Even if they do not, your roofing contractor may determine that an inspection is necessary to ensure the roof can hold the new vegetation.

Additional Considerations and Costs

• Permits. Some locations require permits for green roofs, while others have ordinances that forbid them. Check with your town or city hall for more information.
• Colors. Green roofs can include plants with many hues and shades growing on them. They complement a wide range of house colors but do particularly well with any “natural” or nature-inspired color palette, including fieldstone grays, creams, tans, and some shades of green.
• Technological advances. Green roofs have been around for centuries. But they have only gained popularity lately because of their benefits and the fact that it is possible to have thinner and lighter roofs, making them more accessible.
• Longevity. Green roofs are not known to leak, and some people think they last longer because the plants shield the membrane from UV light.
• Roof type. Seeded and planted green roofs tend to perform better long-term than modular green roofs.
• Incentives. Some areas may have incentive programs that offset costs. However, many green roofs pay for themselves in the long term with lowered energy costs.