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.

There are several types of green roofs, which leads ¹ to a wide range of associated costs. The average homeowner, creating an extensive green roof for a 1,500sq.ft. roof, can expect to spend between $15,000 and $30,000, with most paying around $22,000 for the project.

Green roof installation

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Pros and cons of a green roof

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. 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.

Types of green roofs

Most people consider three basic types of green roofs, along with two subsets that may be used in special cases. For residential purposes, only extensive roofs are an option, unless installing on a multi-residential building.

Extensive Roof

An extensive green roof is the most common and least expensive type of green roof, with costs ranging from $10 - $20 a square foot ². 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.

Semi-intensive roof

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. Costs start at $15 a square foot ² and range to about $30 a square foot ². They require more care and maintenance, as well as irrigation, but can provide a more sculpted appearance.

Intensive roof

Intensive roofs are very heavy, with a thick layer of soil. They allow the most customization for the rooftop but are the most expensive, with costs ranging from $25 - $35 a square foot ². They must be installed on a flat, concrete roof and require a lot of care and maintenance as well as irrigation. These are not normally practical for residential buildings but can produce extremely dramatic and beautiful results.

Blue-green roof

The blue-green roof is designed for city usage in areas that see very heavy rainfall and 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. They cost $25 - $35 a square foot ².

Bisolar roof

A biosolar roof is a green roof that has solar panels installed. It may be intensive or semi-intensive and usually has modular growing mediums rather than complete coverage. The green roof portion costs between $25 - $35 a square foot ², with the solar panels costing an additional $18,000 - $20,000. They are not normally installed on residential roofs due to the weight.

Roof 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.

Plants

Plants for a green roof vary, depending on the area where you live and your climate. Just 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 also plant grasses and a range of other plants. Some of 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.

Modular vs built-in system

Depending on the type of green roof you choose and the pitch and material of your roof deck, you may be able to have either a modular or built-in ³ system. Modular systems involve using plants in trays, so you can better customize the appearance of the roof and create walking paths. The trays, however, are usually heavier and reserved for commercial buildings with concrete roof decks and intensive systems. Extensive rooftops are generally built-in with total coverage because they are lighter and can be installed on a variety of roofs, including those with moderate pitches and standard plywood ⁴ roof decks.

Irrigation

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 ⁵ 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.

All green roofs should be irrigated in the beginning to allow for proper plant growth and help the plants take hold. For a residential home, this is usually done with manual irrigation using a garden hose and spray attachment for the short time necessary. After the initial growing period, extensive green roofs do not require additional irrigation.

Installation process

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, and some roofs require substantial work before installing a green roof.

A roof barrier, which is usually a type of heavy plastic, is spread over the roof to make sure that the roots do not penetrate the roof deck. If the roof has walls or if there will be walking paths, these are lined with some kind of 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 will hold the growing media or soil.

Soil is placed on the filter fabric, and then the plants are installed. This may be done through seeds, by planting seedlings and small plants, or by installing trays of ready-grown plant material. Installation takes place over roughly 5 to 7 days, but it will take several weeks for the plants to establish themselves.

Labor

Labor makes up a significant portion of the cost of a green roof, mostly because the process of creating one can be labor-intensive. Getting the materials onto the roof, constructing the layers, and installing the plants is extremely time-consuming and can cost $5 to $10 a square foot ² in labor.

Roofs with a steeper pitch or have very intricately designed patterns for growing cost significantly more than roofs that have seeds mixed into the growing medium prior to installation. For a 1,500 sq.ft. roof, expect the labor portion to make up roughly $10,500 of the $22,000 total.

Maintenance

The amount of maintenance your green roof requires has a lot to do with 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 of care as any decorative garden bed. You also need to irrigate regularly and check to ensure that the drainage systems are operating 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.

Enhancements and improvements

Roofing inspection

Unless you have a new roof installed to support a green roof, your existing roof should be inspected prior to installation. Roofing inspections cost anywhere from $50 - $500, depending on the size and level ⁶ of inspection.

Additional costs and considerations

• Some locations require permits for green roofs, while others have ordinances that forbid them. Check with your town or city hall for more information.
• 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.
• 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.
• 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.
• Most homes can benefit from a green roof, whether from green building certification to the aesthetics of a rooftop garden.
• Green roofs are not known to leak, and some people think they last longer because the plants shield the membrane from UV light.
• Seeded and planted green roofs tend to perform better long-term than modular green roofs.
• Some areas may have incentive programs that offset costs. However, many green roofs pay for themselves in the long term with lowered energy costs.

Remodeling Terms Cheat Sheet

¹ Leads: A naturally occurring heavy metal that is highly toxic to humans, and has been used in paint, gasoline, piping, and other applications

² Foot: A support for the foundation of a house that also helps prevent settling. It is typically made of concrete reinforced with rebar, but can also be made of masonry or brick. It is usually built under a heavier part of the house like a wall or column, to distribute the weight of the house over a larger area.

³ Built-in: An item of furniture, such as a bookcase or set of cabinets, that is built directly into the structure of the room. Built-ins are therefore customized to the room and not detachable

⁴ Plywood: An engineered construction material manufactured from thin slices of wood glued together in alternating grain patterns for strength

⁵ Irrigation system: Set of equipment used to irrigate lawns