Intensive vs Extensive Green Roofs: What’s the difference?

 

Components of an intensive green roof (click for high-res version)

Intensive

Intensive green roofs are widely used on commercial buildings where owners want to have large green areas that incorporate all sizes and types of plants. These roofs will have grasses, ground covers, flowers, shrubs and even trees. They will often include paths and walkways that travel between different architectural features to provide space where people can interact with the natural surroundings. Benches, tables, planter boxes, greenhouses, ponds and fountains offer people places to relax, dine or work in park-like settings.

The intensive green roof uses planting mediums that have greater depth than the extensive green roof.  This deeper soil allows intensive roofs to accommodate large plants and dramatic plant groupings. Another term for these green roofs is “rooftop garden.” Intensive green roofs require more maintenance because of the plant varieties they will support. Vegetable and herb gardens fit in well on these rooftops and to a degree their care is slightly easier than ground level gardens since fewer pests and weeds find their way to the higher elevations. All plants will have fertilizer and water needs and many will require clipping and pruning. These green roofs tend to stay more attractive in dry weather and are very often irrigated.

The planting medium in intensive green roofs starts at 6 inches (although you will see some wiggle room in various definitions) and really elaborate designs may exceed a couple feed.  Once the plants are installed and the soil is moist these rooftop green spaces can weigh as much as 150 pounds per square foot. The irrigation and drainage systems have to operate at peak efficiency to reduce the chance of overloading the roof’s structure.

Extensive

Extensive roofs (click here for more) are more often used for single family and multi-family residential buildings. They are also best suited to spaces where people are seldom going to be walking on the roof surface. People walk on them mainly for maintenance. These green roofs also fit outbuildings like sheds and garages very well. Other names include “low profile” and “performance.” The design is supposed to give high performance to water use and thermal advantages, while keeping the overall weight of the roof low.

The planting medium in extensive green roofs ranges from 1.6 to 6 inches deep and while deeper systems have been installed they are not favored as much as the shallower systems.Drought-tolerant sedums (succulent plants) and grasses are the typical plants used since they are shallow-rooted and use little water.Plant diversity on these roofs is kept low to simplify care and to be sure all plants have similar moisture requirements. During dry times these rooftops may turn brown, only to revive with rain.

Extensive green roofs are the simplest to install and are very often added to existing roofs. Depending on the source you look at these roofs may add 10 to 35 pounds per square foot to a roof’s load.

A variation of the extensive green roof is called semi-extensive. You can get a wider variety of plants suited to the conditions offered by this option. The soil will be up to a foot deep and not require irrigation.

The extensive green roof is the typical choice for homeowners, but if you are building a home you can enjoy the wider options offered by the intensive green roof because it can be included in the plans, saving the costs of retrofitting an existing structure.

———–

For more green roof tips and tricks, you can subscribe to this site’s RSS feed and sign up for my free email mini-course using the box below.

Questions?  Comments?  Feel free to shoot me a comment – I will try to respond to all of them.

4 Responses to Intensive vs Extensive Green Roofs: What’s the difference?
  1. Green Roof FAQ | Green Roof Plan
    August 2, 2010 | 4:45 pm

    [...] two main types of green roofs are, extensive and intensive. Extensive green roofs use a very shallow growing medium with plants [...]

  2. Mpizopoulos Dimitris
    September 16, 2011 | 5:02 pm

    hey there!!
    do u think that thermal,solar and visible absorptance is different to these types of green roof?

  3. AdmiralSal
    May 21, 2012 | 9:00 pm

    I was turned on to this by a group on facebook. (Homesteading/survivalism) and then linked here. Some of this info is cited, though I did not actually check the cited studies.

    Hope this helps:

    Green roofs are excellent insulators. Studies have shown that a green roof can reduce your cooling costs by 50% and more during the summer months and in the winter your home will retain 15-30% more heat than if you had a conventional roof. On a sunny, 80-degree-F day, a black roof can reach 180 degrees F; a white roof 120 degrees; and a plant-covered roof 85 degrees. Save money and use fewer energy resources.

    Cost. There are many modular green roof kits available that might bring the costs down. Extensive green roof: $8 to $20 per square foot. Intensive green roof: $15 to $50 per square foot. A 2006 study by the University of Michigan comparing costs of conventional and green roofs showed that, on average, installing a green roof costs about $22.00/sq. ft. versus $16.00/sq. ft. for a conventional roof. In its life, however, it was estimated the green roof would save over $200,000 (in 2006 energy prices) with two-thirds of that coming from reduced energy needs.

    Reduced storm water runoff. When the water falls on a typical roof, it’s often funneled off into storm water drains, collecting pollution along the way and polluting our waterways or increasing the amount of sewage to be treated. Green roofs ‘harvest’ rain water and put it to beneficial use.

    Increased longevity of roofing membranes. The plants and growing medium are absorbing the solar rays, protecting the roofing materials from UV breakdown.The green roof also shields the membrane from extreme temperature variations, another cause of hastened degradation. According to Penn State research, a green roof will lengthen roof life by two to three times.*

    Sound proofing. An extensive green roof can reduce sound from outside by 40 decibels, while an intensive roof can reduce sound by 46-50 decibels (Peck et al. 1999).

    Aesthetic appeal. Nature relaxes, promoting psychological well-being.

    Carbon is sequestered. Through the process of photosynthesis, carbon dioxide is removed from the atmosphere and stored as carbon in biomass.

    Urban Heat Island Effect – if an urban area has numerous green roofs, heat island effect is lowered.

    Habitat. When planted with native vegetation – a green roof becomes a habitat for indigenous species and migrating butterflies, birds and bees.

  4. [...] roofs have growing mediums that are over 6 inches deep; extensive roofing systems go from about 1.6 inches to 6 inches deep. And since I already said that intensive green roofs are often found on commercial buildings, [...]

Leave a Reply

Wanting to leave an <em>phasis on your comment?

Trackback URL http://www.greenroofplan.com/intensive-vs-extensive-green-roofs/trackback/