Biosolar Roofs: The Ultimate Green Roof System

Green roofs are slowing taking over, with benefits ranging from better stormwater management to energy efficiency. And although the market and technology has fluctuated over the last decade, solar energy has become increasingly cheaper and more efficient, making it a perfect addition to any development project. Many developers opt for either a green roof or a solar panel array, or if they have both, often separate them in the design of the roof. But there are a lot of surprising benefits to having solar panels atop the vegetative platform on a green roof: enter the Biosolar roof.

A Biosolar roof is a green roof that combines the power of solar by building the array directly on top of a vegetative medium. You might be thinking this particular structure is too crowded, difficult to maintain, or too expensive. But in actuality, you are getting the best bang for your buck with this system, and the environmental benefits are great too.

Structurally speaking, a green roof makes a perfect ballast for the a-frames required to support a solar panel array. This allows installers to use the growing medium as a support for the panels without attaching the a-frames to the waterproofing membrane or the actual roof structure itself (further protecting the additional waterproofing benefits that a green roof provides)(1).

Vegetation also increases the efficiency of the the solar panels. Despite the amount of sunshine that may come with them, hot days do not help solar panels work better. Temperature plays a huge role in the energy production of a PV panel on a given day. And since vegetation cools the ambient temperature of a roof through evapotranspiration, placing the panels atop a green roof structure can make the payoff of your solar panel array much higher. Plants can also, in many cases, reduce the amount of airborne pollutants and dust, allowing the panels to absorb more sunlight (1).

Biosolar roofs also create a more diverse habitat through it’s unique stormwater runoff abilities. Due to the slanted nature of the PV arrays, a biosolar roof typically has three micro-habitats: one that is very moist due to the runoff of the panel, one that is dry and cool beneath the shade of a panel, and one that is ideal for growing sedum, a popular plant choice for green roofs. This level of micro-biodiversity is not often found in urban environments, so a Biosolar roof can help cultivate additional wildlife and nutrients for plants (2).

Although careful consideration for plant species, spacing of panels, and other factors should be considered in the design, a Biosolar roof can maximize the benefits of both solar energy production and vegetation at roof level.




What Do You Plant on a Colorado Green Roof?

With the new green roof ordinance in Denver, you might be seeing a lot more green towards the sky in the mile high city. But what sort of plants can survive the windy arid environments of a rooftop in a state like Colorado?

Sedum plants (more commonly known as stonecrops) are leaf succulents with up to 470 different species. Their flowers (which often have five petals) add a nice decorative element to green roofs that are installed for functionality and cost savings. Because their leaves retain water they are preferable to grass on green roofs, especially for modular systems (4). The EPA Building in Denver has an extensive modular green roof with a primarily sedum cover. Some of the variety of sedum plants used are Sedum acre, Sedum album, Sedum kamtchaticum, Sedum spurium ‘Dragon’s Blood’, Sedum spurium ‘John Creech’, and Sedum spurium ‘Red Carpet’ (3).

Other succulents, such as aloe vera, are also great plants to have on a green roof, especially one that is accessible. Many succulent plants have a unique and ornamental appearance, so they are perfect for green spaces while also perfect for the arid climate of Colorado. A study conducted by Colorado State University found that the succulent species overall as a group (compared to other species tested) maintained a healthy state five time longer than the next best species tested (herbaceous). Their revival rate was double that of others (1).

Beyond water retaining plants such as succulents and cacti, prairie grass such as Blue grama is also a popular choice for green roofs in Denver. The flagship REI store green roof features this particular grass, as well as a combination of shrubs and perennials (2). It also happens to be the official state grass of Colorado, and is often found in our beloved Rocky Mountains.

Last but certainly not least is our favorite plant selection for green roofs: food. Despite what you might assume, green roofs are great environments for planting vegetables, herbs, and various other edible goodies. Because of their highly contained environment, away from the garden variety of pests and plant diseases, they give plants an opportunity to thrive much like a container garden. Don’t believe us? Just ask The Gathering Place, Denver’s own daytime drop-in center for women and children experiencing homelessness. Their roof features a safe playground and garden that supplies some of the food used in the kitchen. The kids are often involved in the caretaking of the plants, making it educational and fun to boot (2).

Now that you know what sort of plants you can grow in Colorado, maybe you’re thinking a getting a green roof yourself!


  1. Extensive green roofs in Colorado: Plant... (PDF Download Available). Available from: [accessed Jun 07 2018].



The How Urban Heat Island Effect Impacts Public Health

Here at Sow Green, we have a pretty deep affection for green roofs. And it’s no wonder, they have so many benefits to both the private sector and the community that we can’t help but think they’re a pretty great solution to some of our biggest problems. One of those that we mention often is the Urban Heat Island (UHI) Effect. But what exactly IS a Urban Heat Island, and why are this so dangerous?

A Urban Heat Island is a metropolitan area that is significantly warmer than the surrounding rural/suburban areas due to urban development and human activity. Dark impervious surfaces, such as black rooftops, parking lots, and roads absorb higher levels of solar radiation, creating a pocket of heat and an increase in average temperatures. Urban areas also have much less vegetation, and therefore the level of evapotranspiration (the cooling of an area due to plant growth) has decreased (4). Urban Heat Islands have been associated with an increase in heat-related illness and a myriad of other public health issues.

The year 2017 was the third hottest year on record in the United States, and extreme heat is a leading cause of weather-related deaths, with over 1,000 people dying per year.

But not everyone has the same level if risk. According to the National Environmental Education foundation, children, the elderly, the sick, and people without access to air conditioning are at greater risk of heat-related illnesses. In the City of Denver alone, almost 50% of the population does not have air conditioning in their homes (3). People with mental illnesses such as depression or schizophrenia are also at a greater risk, since their medications may interfere with temperature regulation. Increases in death by suicide also correlate with high temperatures, as do crime rates and aggravated behavior (1,4).

The issue is not isolated to the United States, in fact people who live in developing countries are at an even greater risk. In 2015, Karachi, Pakistan lost at least 1,200 people to heat related illness, the majority of which were the elderly, sick and homeless. Government officials reportedly did not act, and Pakistan is due for another formidable summer this year (2).

Of the top 10 cities with the most intense summer urban heat islands, Denver ranks third only behind Las Vegas and Albuquerque. With average daily urban-rural temperature differences of around 5 degrees Fahrenheit, you can expect a hot day to get much hotter in the mile high city.

So what can we do to mitigate our Urban Heat Island? Green roofs reduce the amount of impervious surfaces by replacing black rooftops with vegetation that can cool the surrounding areas, while also cooling the building below. In addition to green roofs, cool or white roofs are also an economical method. Adding trees to a community can reduce ambient and surface temperatures by almost 10 degrees Fahrenheit. Protecting green spaces such as parks and community gardens can also have a positive impact on urban temperatures.

With better urban planning and policies that increase the development of green spaces in our cities (such as the new green roofs ordinance in Denver), we can reduce the public health risks of the Urban Heat Islands and create healthier, more just communities.






How Green Roofs Efficiently Utilize Water in Drought Prone Areas

Many Denverties may be concerned that more green roofs could have a negative impact because too much water is needed and we live in an area prone to drought. We want to explain how green roofs impact water quality, and best practice irrigation methods to efficiently use water.

Although it is true that green roofs need a little extra water in the first few years of development, they also decrease runoff which helps manage stormwater and reduces flooding. Pervious surfaces (such as grass, dirt, and sand) retain water, while roads and sidewalks don’t causing water runoff. Green roofs also reduce water pollutants in our streams and lakes, as plantlife filters out pollutants. Water quality and quantity therefore will not be affected, as the positive and negative benefits impacts cancel out. There is also reduced energy usage and cooling reduction from green roofs, which provide water savings. Green roofs reduce urban heat island which can reduce the cooling needs of other buildings. And since most green roofs use sedums which are drought resistant, over time they do not require much water (1). Therefore, green roofs will not cause water issues in a high drought state.

Water used for irrigation is important to avoid replacing plants because of heat or drought, and to also provide fire protection. The amount of irrigation needed depends on the size of the project, the plants water needs, regulatory requirements, and growing media. Extensive green roofs with shallow growing media and drought resistant plants like sedums will need much less water than an intensive green roof with trees and diverse vegetation.

The type of irrigation method will ultimately affect water usage, but luckily there are many options that help conserve water. For smaller extensive green roof projects, you can use a manual irrigation (such as a water hose) that is low cost and uses small amounts of water when needed. If you are using this method, be careful of damaging plants while dragging a hose, and with temporary irrigation methods watering is often neglected. For permanent irrigation, low volume drip irrigation will provide water slowly and directly into the growing medium where it is needed. This is a highly efficient application that requires a higher water quality. Moisture retention layers are also a good form of passive irrigation that uses “egg carton” depressions to store small amounts of water when it rains. This of course relies on rainfall, only working in wet conditions and would be hard as the only irrigation method in a city like Denver, but could help offset some water usage in the long term.

There are also ways you can reuse water. Colorado has strict water rights laws and recently allowed a small amount of rain barrels, but only for residential (2). The current Green Roof Initiative will even need to change the wording around rainwater reuse, as it currently conflicts with Colorado law. That being said, you can integrate with other building systems and create a grey water recycling system to help irrigate a green roof. Grey water is reusing non-potable water from baths, showers, and sinks. Another popular way to reduce water usage is with HVAC condensation. This method uses condensation recovery to harvest water from your HVAC system. The Austonian has a green roof with pressurized irrigation from HVAC condensation and Austin, TX City Hall has built a scenic waterfall on their green roof with HVAC condensation (3).

To reduce your water usage on a green roof, ensure the design team knows your goals and can figure out location, access, plants and size accordingly. Make sure to include irrigation in your budget and maintenance plan, or plants will have a hard time surviving.


  1. (pg 36-45)



Are Green Roofs a Fire Hazard?

In the US, all roofs must meet fire resistance requirements in order to comply with International Building Code. But do green roofs pose a greater fire threat than a traditional one? Historically, roof fires have primarily been a result of negligence of the end user. But in most cases, green roofs can actually be a great fire mitigation method. In fact, the first green roofs constructed in Germany were initially used as fire prevention systems! (1)

This of course is only true with proper design and maintenance. Green Roofs for Healthy Cities actually aided the development of the ANSI/SPRI VF-1 External Fire Design Standard for Vegetative Roofs to help designers and building owners ingrain the necessary fire protection into the green roof system.

Although the presence of vegetation can at times pose a fire hazard, fires can be mitigated with the right selection of plant life and proper design. Sedum and succulent species for example are drought resistant and hold onto water for a longer period of time than many other plants. This makes them less prone to ignite in the case of a spark or other fire hazard. Also, it is important to have vegetation free zones around the periphery, as well as around exhaust vents.

In addition to proper plant selection, maintaining the roof well is also essential. Weeding, removal of dead plants, litter prevention methods, prohibition of smoking, and testing the irrigation regularly are all great ways to ensure that you are reducing the risk of fire on the roof. It is also a great idea to communicate fire safety to occupants in regards to the use of cigarettes or barbecues. 

Many green roofs require irrigation systems, which can not only mitigate fires on the roof but can aid in preventing the fire from spreading. But even if an irrigation system isn’t required, it might be a good idea to incorporate for fire safety. This is especially true if the roofs plant selection includes a lot of grass or trees.

Other considerations, such as the height of the building and strong winds can factor into fire safety methods. The ANSI/SPRI VF-1 standard references methods for testing these, but you may also consult with a wind design engineer if you feel your building requires it. It should also be noted that many of the waterproofing layers required for proper installation of green roofs have built in fire retardant materials. This can be especially helpful in protecting the building below.

Lastly, it is the responsibility of fire marshals to inspect the roof for any possible fire hazards (3). Being familiar with fire safety standards can help you prepare for the routine inspection visits. As with all safety regulations, it falls on the building owner to create a safe environment for occupants. But planning ahead and using these national standards as a guide can make your green roof not only fire safe, but fire resistant.


  1. Green Roofs for Healthy Cities

  2. ANSI/SPRI VF-1 External Fire Design Standard for Vegetative Roof


Green Spaces Improve Our Capacity to Learn

Last week we wrote an article about how the healthcare industry is integrating green spaces into the design of their facilities to improve patient recovery and save on operational costs. It makes sense since the industry accounts for over 17% of the U.S. GDP. But there are other places that can be improved by adding a little dose of nature, and one such place is schools.

The United States spends over $661 trillion annually on K-12 education (1). And yet, despite this, many schools are underfunded and many teachers underpaid. Therefore it is incredibly important that each dollar spent on education is delivering the best learning environment possible, and when it comes to providing this environment the data (once again) points toward biophilic design.

Students absences create additional expenditures that can be mitigated by integrating daylit classrooms and view of nature. A study conducted in 1996 by Michael Niklas and Gary Bailey found that schools with optimal daylight allowance had increased attendance by 3.2-3.8 days per year compared with attendance at none daylit schools. Niklas and Bailey calculated that the value for 3 days of attendance for the 633 students in the school district where the study was conducted was about $126,283 in tax dollars saved (2).

Another study in 1999 found that students perform and learn 22-26% faster in daylit classrooms (higher performance was indicated when students had a view of nature through the windows of their classroom) (3). The same study estimated that schools who invest in better daylighting for students can improve test scores by 5-18%. And as is the case with the healthcare industry, teachers and staff also have improved performance and mental focus in daylit environments.

Green spaces have also shown to have a positive influence on children diagnosed with ADHD and ADD, improving concentration and attention rates (5). Over $2 billion each year is spent on medicating the over 5.2 million children diagnosed with ADHD in the United States (6). By utilizing biophilic design, we can collectively save parents several hundred dollars a year on medication for attention deficit disorders, while improving the quality of life for their children.

So beyond saving schools money, how does a better education for students stack up for the economy overall? The Alliance for Excellent Education found that if all the students who dropped out of high school in 2007 had graduated, they would have collectively earned an estimated additional $329 billion in income over their lifetime (4). The costs of not improving our schools is staggering to both the individual and the communities where they live and work.

Although nothing replaces improvements in curriculum and the schools resources, biophilic design can be an additional means (and more meaningful investment) in the students learning and development.


  1. US Census Bureau. Current Population Survey, Annual Social and Economic Supplement. Washington, D.C. 2010.

  2. Niklas, Michael H., and Gary B. Bailey. “Student Performance in Daylit Schools.” Innovative Design. Raleigh, North Carolina. 1996.

  3. Heschong, Lisa. Heschong Mahone Group. “Daylighting in Schools: An Investigation into the Relationship Between Daylighting and Human Performance.” California Energy Commission: Pacific Gas and Electric Company. Fair Oaks, California. 1999.

  4. Alliance for Excellent Education. “The High Cost of High School Dropouts: What the Nation Pays for Inadequate High Schools.” Issue Brief. 2007.

  5. Taylor, A., and Frances E. Kuo. “Children With Attention Deficits Concentrate Better After Walk in the Park.” Journal of Attention Disorders. No. 12; 402. SAGE Publications. 2009.

  6. Scheffler, Richard M., Stephen P. Hinshaw, Sepideh Modrek, and Peter Levine. “The Global Market for ADHD Medications.” Health Affairs, 26, No. 2 (450-457). 2007.

Why Healthcare Facilities are Designing Nature into Patient Care

Do you enjoy being in a hospital? Many people would say, no. If you find yourself in a hospital you are most likely (with the exception of a child’s birth) not there for a good reason. It doesn’t help that many hospitals are drab, sterile, and colorless environments. But many healthcare facilities are wising up and adding elements of biophilic design (incorporating nature into design) to improve patients health and recovery by making their stay more pleasant, naturally.

An increasing number of new hospitals and healthcare centers are designing more green spaces, access to natural light, and views of nature from patient rooms into their initial construction. Studies have shown that biophilic design can influence faster recovery, lower the use of postoperative medication, reduce the stress of staff, and improve emotional wellness (1). And that translates into some serious cost savings.

A study by Roger Ulrich in 1984 found that patients recovering from gallbladder surgery and whose windows overlooked a scene of nature where released 8.5% sooner (2). Another study in 2001 found that bipolar patients with rooms that had direct morning sunlight were released on average 3.67 days sooner (3). By reducing the length of patient stay by half a day, hospitals can save $93 million in operational costs every year (1).

Green spaces can also affect a patient's dependency on pain medication. A study in 2003 conducted at a teaching hospital in Baltimore found that patients undergoing a Flexible Bronchoscopy surrounded by pictures of nature and nature sounds experience better pain control during the invasive procedure (4). Another study in 2005 found that patients with 46% more sunlight in their rooms perceived less pain and accumulated 21% less in pain medication costs for the length of their stay (5). Hospital staff too can benefit from biophilic design, as they often experience the same reduction in stress when surrounded by nature, and are able to provide better care as a result.

The methods of including natural elements into healthcare design vary. Lucile Packard Children's Hospital Stanford is a LEED Platinum certified building that has 3.5 acres of gardens and green space, including a green roof. Every nursing unit has an outdoor view, and outdoor planters in the solar shading system provide a connection to nature for every patient (6). The Anschutz Wellness Center at CU Aurora integrated a small green roof garden with seating areas for a quiet nature retreat (7). Many hospitals are now using the data accumulated since Ulrich’s initial study to use garden and outdoor spaces as part of the treatment process (8).

Although spending time in a garden won’t cure someone of cancer, it can reduce pain and stress, which can give a patient’s immune system the boost it needs to heal more effectively. And with healthcare accounting for more that 17% of our nation’s GDP, faster recovery on a grand scale can have a huge macroeconomic impact. Clearly integrating green spaces with healthcare has far reaching benefits for patients and the industry at large.



  2. Ulrich, R. S. “View through a window may influence recovery from surgery” Science, Vol. 224. 1984.

  3. Benedetti, Francesco, Cristina Colombo, Barbara Barbini, Euridice Campori, and Enrico Smeraldi. “Morning sunlight reduces length of hospitalization in bipolar depression.” Elsevier Science Ltd., Journal of Affective Disorders 221-223. Milan, Italy. 2001.


  5. Walch, Jeffrey M., Bruce S. Rabin, Richard Day, Jessica N. Williams, Krissy Choi, and James D. Kang. “The Effect of Sunlight on Postoperative Analgesic Medication Use.” Psychosomatic Medicine 67:156-163. 2005.




Making Developers Pay: Why Environmental Regulations Hit Real Estate Hard

When the Initiative 300 movement began, it received a lot of opposition from local developers. Many claimed that incentives would be better, and that is was unfair to enforce or impose the installation of a green roof on large real estate projects. Some developers, such as Kyle Zeppelin, supported the Initiative. A long time implementer of green roofs, Zeppelin claims that beyond the environmental benefits, the green roofs add value to the projects and are more attractive to potential renters and buyers (1).

But should the cost of environmental and social impacts be imposed on developers? A study conducted by the SETO Lab at Yale University on the environmental impacts of urban growth stated that “the conversion of Earth’s land surface to urban uses is one of the most irreversible human impacts on the global biosphere (2).” It claims that the rapid loss of productive farmland, loss of biodiversity, and loss of vegetation will contribute to a rapidly changing climate. It can also cause environmental stressors for urban residents such as the Urban Heat Island effect, increase in air pollution, and a decrease in access to healthy food and clean water. And then there’s the flooding.

For instance the disastrous flooding in Houston, TX  following Hurricane Harvey was a lot less about weathering the storm and much more about city’s design(3). Too many impervious surfaces and a lack of restrictions on developers building in floodplains cost residents and disaster relief organizations an estimated $180 billion (3). The $180 billion is paid by citizens and not developers who created the concrete city.  

Green roofs are an excellent stormwater mitigation strategy, reduce the Urban Heat Island effect, and improve air quality. They can also be used for urban farming, reducing the loss of farmland cause by urban sprawl. Denver is one of the fastest growing cities in the United States, and we have an opportunity to learn from the mistakes of other large metropolis areas. We can set a standard for urban development that won’t cost taxpayers a fortune down the road.

By enforcing regulations and ordinances that ensure developers are investing in environmental mitigation strategies, local governments are protecting the city’s future. A future that includes positive growth and development, which helps developer’s bottom line. In order to solve our largest climate problems and ensure our cities future, everyone has to help.   






Are Green Roofs Going to Raise My HOA Fees?

Denver is growing, and the purchasing of condos and other multi-family units is growing as Downtown becomes the fastest developing sector of the city. Many homeowners in multi-family buildings getting a green roof under the new city ordinance might be wondering if the newest renovation will raise their Homeowners Association (HOA) fees.

Typically maintenance of a green roof is most extensive during the first five years, in order to help the newly planted vegetation take root and to make any unforeseen modifications. After that, many green roofs do not require as much attention, and maintenance costs will go down. In fact, many green roof installation contracts include maintenance for the first few years, so often those casts can be paid upfront (1).

And since the lifespan of a green roof is often twice as long as a conventional roof, even with the additional maintenance the overall lifespan cost of a green roof is less per year on average (2). Instead of saving for a roof replacement in 15 years, building owners can put that money towards additional maintenance costs knowing that they won’t need to replace their green roof any time soon. Green roofs also lower the costs associated with unexpected storm and hail damage.

Even with these considerations, many building owners may raise monthly fees to accommodate for the additional amenity of a green roof. Although it may not seem fair to pass this down to residents, there is still no need to worry. Why? Because green roofs will lower your electric bill!

On average, green roofs will lower energy costs in the summer and winter, through additional insulation and evapotranspiration. They also reduce the heat island effect, which can cause an increase in 5%-10% of energy usage in the summer (3). What’s more, a green roof can add additional amenity space with a great view of our city! This is great if your condo or apartment doesn’t have any green space for you to access.

Theoretically a new green roof shouldn’t affect HOA fees, but the cost savings and added benefits of a green roof can more than make up for it.



  2. Porsche, U. and M. Kohler. 2003. Life Cycle Costs of Green Roofs: A Comparison of Germany, USA, and Brazil. Presented at the World Climate and Energy Event. December 1-5, Rio de Janeiro, Brazil.