MetroVerde Green Roof FAQs

What is a Green Roof?

Typically, a Green Roof is comprised of a collection of plants, housed and framed together in a metal, wooden or plastic container and installed above a conventional roof. 

The two most common types of Green Roofs are Extensive Green Roofs and Intensive Green Roofs.  An Extensive Green Roof normally has a very thin layer of soil and supports low growing plant species adapted to harsh environments.  Intensive roofs have frames holding deeper soil layers, six inches or more, supporting a wide variety of plant species.

Intensive Green Roofs usually require irrigation and regular maintenance.  Due to significant weight loading factors, they must have structural engineering consideration applied before installation to make sure the roof is capable of supporting the additional weight.   Intensive Green Roofs can provide attractive landscaping.

Extensive Green Roofs have a smaller layer of soil medium and weigh less, however all Green Roofing projects should still undergo structural engineering analysis.  Extensive Green Roofs are normally planted with vegetation that typically do not require artificially delivered irrigation.  Although the quantity of species suitable for Extensive Green Roofs is more limited, the skilled vertiscaping designer can specify species combinations that will produce stunning color.

A properly designed Green Roof system can be added to most existing or new residential, commercial or institutional buildings.  Always consult a Green Roof professional and structural engineer to determine if your existing or proposed roof is suitable for a Green Roof application.

Is the color of my Green Roof really 'Green'? 

The color of your Green Roof depends upon plant species selection.  Foliage colors range from green to yellow to blue to red hues.  Many Green Roof plants offer as stunning array of flowers, and properly designed can offer unique and distinguished aesthetics to a residence or business.  Importantly, there has been an exciting new trend of using Green Roof plant design for advertising effects.

What Benefits are there to a Green Roof?

·               Conserves energy through inherent cooling effects as a result of the transpiration release of water from the plants

·               Reduces ‘Heat Island Effect” by shading the roof

·               Contributes to sound reflection minimization

·               Properly installed can significantly increase the service life of a roof

·               Improves air quality through oxygen production, offsetting CO2 and carbon production

·               Decreases stormwater runoff (I was skeptical at this claim at first – but after installing my first Extensive Green Roof – 35 degree slope – I was amazed at the significant amount of runoff reduction)

·      Improves water quality of runoff (Depending on the amount of fertilizer applied to the roof)

·               Provides wildlife habitat (I noted a significant increase in Anole population amounts and Anoles love to eat bugs!  Anoles provide great perfect pest prevention service)

·               Provide a link to nature for humans typically lacking in urban areas

·               USGBC LEED certification credits (can contribute up to 14 LEED credits!)

·               Possible Local, State and Federal tax credits

In what climates do green roofs work?

Green roofs exist around the world in a variety of climates, from cold ecotones to tropical zones.  Upfront advice from a professional horticulturist is essential to the ongoing success of a Green Roof System.

My roof has a very steep pitch, can I use a Green Roof?

Probably, again depending upon a variety of factors.  Though Intensive Green Roofs are more difficult to design on steep roofs, some stunning and beautiful Extensive Green Roofs have been designed and installed on steep roofs.

Because of the effect of gravity on soil media, deep layers of soil compound present stabilization issues on steep roofs.  Some have attempted a variety of erosion control measures to prevent soil loss on steep roofs, however an Extensive Green Roof is better suited to steep slopes due to the reduction in amount of erodable planting medium.

What considerations should be addressed during Green Roof design? 

A few of the important factors to address in a green roof project are:

·               Understanding climate factors such as:

·               USDA Planting Zones

·               Rainfall patterns

·               Temperatures – both annual mean highs and annual mean lows

·               Shade and direct sunlight exposure

·               Underlying roof construction and strength

·               Roof slope

·               Waterproofing and root barrier requirements

·               System drainage characteristics.  Roof drains and gutters location.

·               Maintenance and accessibility

·               Appropriate plant species availability

·               Soil and planting medium composition

·               HOA requirements and/or Municipal requirements

·               Fire ratings

·               Cost

How much weight does a Green Roof add to my roof?

The most important Green Roof weight factor is the saturated weight, or weight when the system is fully saturated with water.

An Intensive Green Roof can add 25 or more pounds per square foot, depending upon the soil depth, system composition and types of plants used.  Some of the more elaborate intensive Green Roofs can weigh up to 50 pounds per square foot.  A structural engineer should always be consulted when an Intensive Green Roof is considered.  Steel, alloys and concrete are usually required to support the loadings.

Alternatively, an Extensive Green Roof usually weighs less than an Intensive Green Roof due to a smaller soil layer.  The MetroVerde GRP’s have an approximate saturated weight of 5.5 pounds per square foot.  Again, it is important to consult a structural engineer when considering a Green Roof.

ASTM standards E2397 and E 2399 address Green Roof weight loads.

What type of soil is best to use in my Green Roof?

Green Roof soil systems should minimize use of compactable and bio-degradable soil components such as peat, coir and pine bark.  Organic content of the soil component should generally not exceed 4-5%.  It is important to use soil mixtures that (A) retain moisture, (B) do not rapidly decay or (C) do not significantly compress in volume.

Most professionally designed Green Roof soil mixtures are formulated from high porosity minerals that allow sufficient drainage, water absorption and aeration.  All Green Roof planting material should conform to ASTM standards, and achieve a code minimum fire rating.

How about waterproofing and root barriers?

Many Green Roofs employ PVC, EDPM and thermoplastic type membranes are typically used to eliminate water or plant root intrusion against the conventional roof surface.  Properly designed and installed Green Roof systems should not contribute to roof leakage.

Properly specified and installed Green Roof system root barriers should prevent roots from penetrating conventional roofing systems.

How do I maintain my Green Roof?

Green Roof maintenance should include periodic weeding (see the discussion below under Green Roof Plants), normal roof inspection around trim, connections and roofing seams.  Historical world wide data has been gathered that suggests properly designed and installed Green Roofs can increase the life of a conventional roofing system substantially.

MetroVerde GRP systems can be easily removed to facilitate any necessary roof repairs.  Unlike other Green Roof systems that use roofing penetrations to attach to the roof, the MetroVerde GRP system uses a patented removable frame that requires no roof penetrations.

Avoidance of most water soluble nitrogen type fertilizers is highly recommended to prevent nutrient pollution during storm events.  The MetroVerde GRPM incorporates a slow release type fertilizer that supports Green Roof plants until the natural organic cycle can establish itself.

What kinds of plants should be used on a green roof?

Plants suited for Green Roofs should have the following attributes:

·               Strong, shallow root system

·               Evergreen, suited for strong, year round foliage (winter aesthetics)

·               Fire resistant

·               Suited to the specific site climate

·               Capable of surviving both drought and heavy rain events

·      Wind resistant (preferably low growing)

• If you have noticed large trucks hauling trees and shrubs on the highway, their plant cargo is usually covered to protect against wind damage.  Wind can quickly dehydrate plants.

·               Possess aesthetic qualities such as color and texture

·      Capable of surviving extreme fluctuations in temperature

• Most temperate areas of the US experienced large fluctuations in temperature.  For instance, a roof in northern Florida may be subject to temperatures as low as 10ºF in the winter and as high as 120º F in the summer.

·               Long lived

·               Note:  A sharp roofscape or vertiscape designer will understand all the above and choose those plants that afford durability, safety and desired aesthetics.

Plants typically do not hold up subject to regular foot traffic and may present slippage and/or safety hazards, therefore pedestrian traffic on Green Roofs should be avoided.  As with normal garden plantings, Green Roof systems require normal maintenance ranging from occasional weeding (though appropriate plant selection can minimize unwanted weed growth).

Selection of plant species must be done by a horticulturist with Green Roof experience.  Plant can include groundcovers, succulents, flowering specimens and selected appropriate native species.  Exotic invasive species are not recommended for Green Roof installations!

Do I need local or state approval to install a Green Roof?

Always check with your local building official and insurance agent.  Some municipalities require a permit, some do not.  Fortunately, with the push for cities to go green, there is often incentive for installing a Green Roof – from expedited permitting to reduced or waived application fees.

What is the cost of a green Roof?

Green Roof costs vary depending upon the slope of the roof, depth of planting media, types of plants, irrigation requirements, size of the roof (square footage) and other factors.  Extensive Green Roofs characteristically cost less than Intensive Green Roofs.  A rule of thumb is Extensive Green Roofs can start approximately $10 per SF not including installation, with the price climbing much higher for Intensive Green Roof systems.  Unfortunately, many larger Green Roof Companies will not consider a project less than 5,000 SF because of mobilization and setup costs.

Your new MetroVerde GRP system should be regarded as an investment into the value of your structure.  Properly installed and maintained, it should deliver many years of aesthetic, environmental and financial benefits.