Top Six Reasons You Should Install a Green Roof On Your Net Zero Home
Why should you install a green roof on your net zero home? Although green roofs have proven quantifiable energy performance benefits for buildings, they are by no means an essential element of a net zero home. Essential elements of a net zero home may include a well insulated, tightly sealed building envelope, proper building massing and glazing orientation, and efficient HVAC and solar panel system.
Then why do we recommend installing a green roof on your net zero home? Building a net zero house is not just about creating an airtight, well insulated, zero energy bubble. Green roofs have become a symbol for the sustainable/net zero building movement, they raise awareness and provide attractive environments for building occupants. Just like a Nike check on a shoe, green roofs seem to have become the logo for the sustainability movement. For this reason, in combination with their performance related benefits, we attempt to incorporate green roofs in our designs whenever possible and appropriate. Below are our top six reasons for installing a green roof on your net zero energy home.
1. Heath, Awareness and Beauty for Building Occupants
Green roofs offer many intangible benefits to a building. Humans naturally seek connections with nature. This is known as biophilia. By incorporating vegetation into the building via a green roof, the architecture can become attractive to humans on a very fundamental level.
Green roofs can provide building occupants with an increased sense of health and well being, they can increase patron occupancy levels, and generate a greater awareness of the environmental impact buildings can have on the environment. A green roof can serve as a symbol of the sustainable movement to the community.
2. Protect Your Roof from UV Rays
Green roof systems can protect your roof from ultraviolet radiation that can deteriorate a roof overtime. Your roof is exposed to temperature fluctuations and is susceptible to cycles of expansion and contraction when left exposed. If you roof if protected from UV rays, it can last much longer and reduce the amount of times that you need to re-roof your building. It is estimated that a green roof system can extend the life of your roofing system by 200 to 300 percent. It is important for building owners to consider this cost savings during the design phase.
3. Reduction of Cooling Loads on the HVAC System
A good green roof system can also help reduce space conditioning loads on your building. Evapotranspiration is a natural process where plants create a thermal barrier on the roof of your building. This thermal layer can help reduce cooling loads of your HVAC system during hot weather. A study by the National Research Council of Canada, showed that a green roof can reduce summer energy demands by more than 75 percent compared to a traditional black tar roof.
4. Fire Resistant Barrier
Plants naturally hold moisture. A properly selected pallet of plants combined with a roof irrigation system can serve as a natural fire protection layer for the building. The irrigation system for the green roof can also be classified as an external fire sprinkler system for the building. When selecting plants for a green roof in an area prone to wildfires, it is best to work with succulents and cactus.
5. Reduces Storm Water Runoff and Increases Permeable Surface Area on Site for Natural Water Percolation
When it rains on a green roof, the rainfall will penetrate and slowly saturate the soil. This will naturally reduce the amount and rate of water flowing off the roof surface. On site drainage/water control systems can then be reduced in size/minimized due to the reduced amount and rate of runoff. This will often result in cost savings for the building owner. Reducing storm water runoff from a site can also help reduce the amount of toxins flowing into the storm sewer and natural bodies of water.
6. Increased Property Value
A green roof can increase property values for the building owner in many ways. These often include increased patron occupancy, increased rental rates and increased resale value of the building. These are a result of human’s natural attraction to nature but can result in realized financial value for the building owners.
Image courtesy of www.liveroof.com
Types of Green Roof Systems: Extensive and Intensive
Extensive green roof assemblies are typically thinner with minimal growing media and drought tolerant plants. These systems are usually lighter weight, require little to no water, and require little maintenance. Extensive systems are normally installed on existing buildings where the roof has not been pre-engineered to hold additional weight or slim roof systems where the depth of the roof package needs to be kept at a minimum.
Intensive systems are green roof systems that are thicker in depth, with soil media greater than six inches. They are generally intended to be walked on by building occupants. Usually an irrigation system is required for an intensive system. The assembly thickness for an intensive assembly is 6 – 36 inches in depth. Intensive roof systems usually will require roof structures that are engineered to hold the weight of a fully saturated green roof. This is why intensive green roof systems are most often installed on new construction.
Images courtesy of www.liveroof.com
Waterproofing For Your Green Roof
Having a good waterproofing system is essential with a green roof. There are several different waterproofing systems that you can use under your green roof. Recommendations may vary based on the exact system. Generally, the best systems to go with are a hot applied asphalt waterproofing, sheet waterproofing, built up roof, or single ply roof.
Before installing your soil and plant medium, you should always test your roof waterproofing system for any leaks. If you have an intensive system where it is planned to have occupants walk on the green roof, avoid putting insulation below your waterproofing membrane. Even rigid insulation can flex and strain the membrane, leading to leaks in your system.
Image showing an example of a green roof assembly. There are many assemblies offered on the market to select from. Image courtesy of Greener Heights
Maintenance and Irrigation of a Green Roof System
There are two types of irrigation systems that can be installed on a green roof. These are overhead sprinklered and a drip system. After talking with several installers and green roof professionals, it seems that most prefer the overhead sprinklered system. Many people feel that drip systems are more difficult to service if any leaks occur and do not perform as well as overhead system. With overhead systems, be cognizant about over spray onto glass on your building. Situate the irrigation system to minimize spray onto the glazing.
Types of Plant Material
We like the green roof systems that are pre-grown and the plants have had time to establish themselves before getting to your site. One of our favorite systems that have pre-grown plants is Live Roof. Each planting module is grown offsite and given time to establish itself. When the modules are established, they are shipped to the site for installation.
The types of plant material that you can install depend on the soil depth. Succulents and lower lying ground cover only require thin extensive systems, whereas taller grasses and shrubs require the deeper soils of an intensive system.
Cost of Green Roofs
It seems that the initial cost of a green roof system may be the main reason why they have not gained a stronger foothold in the industry. Depending on your location, a green roof system can range in cost anywhere between $15 to $38 dollars a square foot. This can be up to three times the cost of a conventional flat roof system. Although a larger upfront cost, home owners and building owners should consider that the roof system will typically last much longer with a green roof installed over it.
If you would like more information on designing a net zero energy home with a green roof, contact us today here.
