Frequently Asked Questions
Living Roof FAQ
Aren't green (living) roofs heavy?
Yes, green roofs can be heavier than traditional roofing materials. Modern construction often allows for a 25 - 35 lbs/square foot live load on roofs, which is at the very low end of a living roof's weight when soaking wet. Planning for 35 lbs/square foot or above is a good place to start; higher load bearing capacity allows more soil which in turn allows more robust plant growth.
Can living roofs be put on sloped roofs?
Yes, and they have been for years. However, as the pitch increases beyond 20 degrees, soil stabilization measures usually need to be installed. It is more expensive, but certainly doable. More shallowly pitched roofs often don't require a drainage layer, which is actually a cost savings.
Do you have to water your living roof?
Yes and no. Installing a rudimentary irrigation system is often a good idea to help the new plants through the first couple of years. These first few years are more stressful as they adapt to their new environment. Having the system in place allows the owner to provide the plants with water in case of an extreme drought. That said, it is certainly possible to design a living roof which requires no supplemental irrigation beyond plant establishment - in fact, that's what we strive to do.
Do you have to fertilize your living roof?
If you choose plants and soils that are native to your area and appropriate to the living roof environment, you should never need to fertilize your living roof - the system takes care of itself. Natural systems recharge soil nutrients by decomposing dead plant material back into the soil; this is exactly what a maintenance-free living roof should do.
What are the benefits of living roofs?
The benefits are numerous for the homeowner/business owner. Consider the following:
-- Reduced energy usage for heating/cooling
-- Protection of roofing from hail, wind and other extreme weather
-- Increased life span of the roof (often longer than 50 years!)
-- Average 80% reduction in roof runoff
-- Increased urban biodiversity
For municipalities, consider the following:
-- Reduced Urban Heat Island Effect
-- Average 80% stormwater retention for precipitation on the roof
-- Reduced heating/cooling energy demand
-- Urban green space where none existed before
-- Increased urban biodiversity
How much do living roofs cost?
Living roofs are typically priced from $5 to $50 per square foot. Most projects with thinner soils and a simple plant palette fall in the $12 to $20 per square foot range.
How long do living roofs last?
Because the soil and plants protect the roofing membrane from UV and weather related damage, living roofs often double or triple the life span of that membrane. Some green roofs in Europe, where the technology evolved, are approaching 100 years old.
What kinds of plants do you recommend?
Our research focused on using native plants to improve the performance of green roofs in drought prone areas. We draw on this knowledge to choose plants that evolved in thin-soiled, harsh environments so that they have a much higher probability of success in the roof-top environment.
What kinds of roofing materials work with living roofs?
Many different types can and have worked on installations across the United States. PVC, TPO, EPDM, and monolithic tar and asphalt based waterproofing solutions are the most common. Issues like seams and organic components can pose issues when plant roots are involved, so we'd like to discuss the specifics of any project before making any recommendations.
Where can I find out more about green roofs in general?
Green Roofs for Healthy Cities runs a great web site loaded with information at www.greenroofs.org.
Can I receive LEED credits for a living roof?
Yes, you most certainly can. Jon and Dave are both LEED accredited professionals and have reviewed how green roofs fit into the LEED v3.0 standard.
A building with only a green roof installed would be eligible for between 5 and 11 credits. A green roof integrated with a LEED project could contribute to an additional 10 - 36 credits.
For more information on the LEED standard, visit the US Green Building Council at www.USGBC.org
Roof Rocks™ FAQ
Where did the Idea for Roof Rocks™ come from?
The idea of using a monolithic, impermeable mulch came from a natural prairie ecosystem west of Forth Worth, Texas, called a glade. Glade systems feature limestone at the surface where the only plant life either grows in cracks or on top of the limestone itself. Plants that grow in the cracks access water stored in softer rock beneath - this water is protected from evaporation by the limestone formation above. Roof Rocks™ work on the same principle, using lightweight concrete instead of limestone.
Why would I use Roof Rocks™ on my green roof?
Roof Rocks™ provide numerous benefits for the living roofs on which they are installed, especially in drought prone areas.
Roof Rocks™ function as permanent, effective mulching for green roof growing media. They prevent water evaporation, reducing or eliminating the need for irrigation.
Roof Rocks™ focus plant growth into a small percentage of the available soil area. Although this may seem counter intuitive, it actually results in a more robust, resilient roof-top community. Green roofs with many annual species are prone to over-germination during rainy seasons making the roof community more susceptible to drought in drier months. Plant stems and roots provide easy pathways for water to find its way into soil and reduce erosion by slowing the water flow.
Roof Rocks™ provide solid footing by spreading the weight of foot traffic over a larger area, providing safer roof access and preventing soil compaction.
Roof Rocks™ were developed to be as light as possible while still maintaining strength and durability. Roof Rocks™ add about 5 pounds per square foot to the wet weight of a roof. Each 9 square foot Roof Rocks™ panel weighs about 40 pounds.
Certainly. The textured surface provides excellent grip, and the tiles are made from reinforced, lightweight concrete, ready for foot traffic.
So, why is it advantageous to cover up most of the soil on my green roof? Doesn't that defeat the point?
What makes these different from pavers?
Roof Rocks™ were developed to be as light as possible, 40% - 80% lighter than the average patio paver.
The surface of Roof Rocks™ has a high albedo, so that it reflects the sun's rays.
Roof Rocks™ tiles feature a natural looking surface molded from the rocky outcropping of the ecosystem that served as inspiration for this product. This provides more than just aesthetic benefits; the surface collects soil and provides habitats for mosses, lichens, and other micro-flora.
The Roof Rocks™ geometric pattern slows water flow, increasing infiltration by maximizing soil-to-water contact time.
The manageable size of a single 9 square foot Roof Rocks™ panel dramatically speeds installation.
If they're so lightweight, won't they just blow away?
Roof Rocks™ are light per square foot and yet heavy enough to resist strong winds. Also, Roof Rocks™ are anchored to the growth media of the green roof as plants grow up through them. Their low profile give them a shallow cross-section to wind, decreasing drag.
Can I buy some to use in my yard?
This is one of our most common questions... yes, please! Contact us here.
