13 Apr 2018

How Green Roofs Survive the Northeast’s Bitter Cold, Blizzard and Thaw

Tips for Spring Maintenance and Repair

When it comes to weather, the Northeast US has seen it all this past winter: sub-freezing cold and heavy snow, interspersed with warm dry conditions up to 60°, heavy rainfall, powerful winds, and returning snow storms pounding the region.

With conditions varying quite a bit from week to week, even trees and power lines being felled in high winds, what can we expect from the green roofs high above ground level, invisible to many, quietly doing their job keeping rainfall on-site, among other important environmental functions.


Fig. 2 High performing extensive system.

Many question how a vegetated roof can survive winter and how it will perform in the Spring. Some people question how the vegetation looks. Does the bitter cold, wind and snow damage the plants? Will the green roof die?  Can it be walked on in winter months for necessary rooftop maintenance?  Does vegetation need to be re-seeded in the Spring? Important questions, to which solutions start at the design phase.

Vegetated or green roofs, whether intensive or extensive, experience the same cycles of growth, flowering and dormancy that occur to plants on the ground level. Vegetated roofs that are properly designed for climates with four seasons, correctly installed and routinely maintained, have a greater probability of survival no matter the season, and the changing conditions.  This article will focus on lightweight, extensive vegetated roofs, as this is the prevalent type of vegetated system in the Northeast US and across North America. Extensive roofs use shallower depth of engineered growing media up to 6 inches and are lighter than intensive vegetated systems.  Growing medium may be the traditional soil-based or a lightweight needled mineral wool made solely of virgin rock mineral fibres, or a combination of both for best water-retention-to-weight-ratio (see Fig 2). Extensive roofs can achieve excellent water retention and are more economical to install and maintain.



In cold Northern climates such as the Northeast US, vegetated roofs start going into dormancy in the Fall to prepare for winter. As rooftop conditions are harsher than at the ground level, the exposed vegetation on rooftops enter into the dormancy cycle earlier than at ground level.

Dormancy is a natural reaction to adverse environmental conditions. It is the plant’s defence mechanism to keep itself alive stopping further growth and conserving energy. It occurs each Fall in preparation for the cold winter. It may also happen in the summer during periods of intense heat and drought, if not irrigated.

Dormancy synchronizes with the environment and can be triggered by a temperature drop or sudden changes in climactic conditions, such as water shortage.

Retreating plants are not dead. Green roofs lose their flowers and change colour in dormancy creating a beautiful landscape of reds, bronze and browns, to deep purples. Coniferus sedum plants retreat to form a dense mat of glossy and fleshy leaves, while the leaves of deciduous sedum species completely fall off.

Designing vegetated roofs to survive

Plant type:

For highest probability of survival, a vigorous, low-growing, drought tolerant plant species such as sedums and mosses is the ideal choice.  These plants are tough and reliable and can withstand harsh rooftop conditions year-round.  Sedums are succulent plants that mostly originate in Northern climates and flourish in harsh conditions. Vegetation that is pre-grown outdoors locally, for several months or over a winter, ensures they are acclimatized to the localclimatic conditions.

Foliar coverage:

Mature vegetation, with excellent foliar coverage (85% and higher), not only offers instant green upon installation but a higher probability of survival with less chance of wind and soil erosion.

Thermal mass:

The needled mineral hydro blanket’s high water retention reduces the need for irrigation and improves plant survivability year round.

Snow accumulation is welcome as it insulates the vegetation.  A blanket of snow shelters the vegetated roof from strong winds and helps the plants retain moisture and the blanket of vegetation shelters the growing medium from wind erosion. In colder plant hardiness zones, or in areas where there are extreme fluctuations in temperature, green roofs require a deeper depth of growing medium to help mitigate the effects of intense temperature and moisture changes.  Additional growing medium acts as a thermal mass helping moderate the temperature and hydrate the plants – helping reduce significant die-back in the winter or during hot summer droughts. Water retention materials such as the needled mineral hydro blanket is used to supplement and replace traditional soil-based growing medium and achieves equal or better water storage capacity while keeping the system weight low.

Wind Uplift:

With the recent introduction of CAN/CSA A123.24 Standard Test Method for Wind Uplift Resistance of Modular Vegetated Roof Assembly, the first

such test standard in the world, it is now possible to ensure you choose the right vegetated system for a specific building or certain elevation.


If there is little or no snow accumulation, and the vegetated roof is subject to high winds, extreme fluctuations in temperature or a particularly severe ice storm, plant desiccation, or “winter burn” can occur where the plant dries out and dies. This may expose areas of growing medium that may be subjected to erosion by high winds. If such damage occurs to the vegetated roof, a straightforward procedure for repair can be followed in the Spring. This repair procedure also applies to other vegetated roof repairs due to excessive foot traffic or due to construction materials left on the plants for extended periods of time.

The repair is done in the Spring using a variety of sedum clippings sprinkled, where needed, to replace the sections that have been damaged or eroded.  Succulent plants such as sedums are easy to propagate. Many can be rooted from a single leaf, others will root quickly from a stem cutting. For areas that suffered erosion, additional engineered growing medium should be added, as required. After the initial planting of clippings, frequent, light irrigation is required to keep the vegetated roof moist and help ensure the plants take root.

Installation Tips:

Johnson & Johnson World HQ, New Brunswick, NJ installation in December 2017.

Pre-vegetated sedum mats delivered to J&J site have almost 100% coverage with mature vegetation.

Many vegetated roofs are installed in the Fall due to the construction schedule and desire to finish the project. In such cases, it is critical to have mature and well established plants as they have greater survivability on rooftops than plants that are immature seedlings. The vegetation may have been disturbed during harvest, transport and installation.  Therefore, after installation, it is important to keep the vegetated system hydrated during the establishment period for the plants to recover and take root and prepare for the coming winter.  It is imperative to have water access on the rooftop. Furthermore, good design ensures pavers or ballast is installed to reduce foot traffic and vegetation damage. In cold climates, particularly when temperatures drop below freezing, foot traffic over vegetation must be avoided as it can prove lethal, leaving foot-shaped patches of dead plants. The damage will be obvious the following Spring and recovery may take several months or may not happen at all. If pedestrian traffic is unavoidable, protective measures must be taken to diminish the impact of damage.  Materials like plywood sheets or insulation boards may be laid over the vegetation temporarily to help distribute the weight on the green roof, and removed at the end of each day to allow plants to recover.

Fall & Spring Maintenance:

Year-round maintenance is key to ensuring long-term survivability as well as the stormwater performance of the vegetated roofs.  One last maintenance check should be done in the Fall as part of the yearly routine.  Vegetated roofs are also known for their ability to protect the roof membrane, however, not taking proper preventative measures can also lead to unforeseen problems.

Fall maintenance includes the removal of debris and inspection of all drainage paths.

In Fall, it is best to remove fallen leaves and twigs from the green roof. Thick layers of leaves and twigs can also stick together to form an impenetrable mat and may lock in too much moisture, potentially causing rot or damage to the plants.

Weed, one last time, before winter sets in. Make every effort to capture the seed pod intact and tuck it away for disposal to avoid seeds blowing away.  Some weeds may be tolerated, therefore maintenance personnel should be familiar with green roof plants and the owner’s green roof aesthetic preference.

Keeping the vegetated roof hydrated into the Fall months helps the vegetation avoid winter’s freeze-drying effect caused by low temperatures and high winds.

If there is an irrigation system, it needs to be winterized around October in nothern States as frost typically sets in soon after. Maintenance crews typically use an air compressor to blow out the water from the irrigation system.

Vegetated roofs should not be fertilized past August, especially with a slow release type fertilizer. Fertilization may stimulate tender growth and compromise the hardiness of the plant. Secondly, plants won’t have a chance to fully take up the nutrients and the combination of high temperatures may cause the plants to burn. Slow release fertilizer is usually applied once, ideally in the Spring.

Assess the performance of the green roof in the Fall and prepare for next Spring.  It is a good idea to document  your visit with photos and record recent weather conditions for future reference and any potential warranty claims.

About Stormwater Capture Co

Our team prides itself in being a hassle-free, one-stop-shop supplying vegetated systems that can be customized to local requirements, with warranty and maintenance support. We also offer ​access to a variety of analytical support service​s such as ​stormwater calculations specific to location ​and building/roof type.

We specialize in supplying green roof systems with​ high water retention-to weight ratio such as the StormCap system. Our premium base layers ​include​ the ​Needled ​M​ineral ​H​ydro ​B​lanket and can be easily cut to fit any shape and design.​

Contact us 855-786-7626 or send drawings to info@stormwatercaptureco.com get an estimate for your project.

Copyright © 2018 Stormwater Capture Co. LLC. All rights reserved.

Numerous municipalities have vegetated roof programs, incentives or requirements with a focus on stormwater management. Here are examples of a policies and incentives that are promoting the growth of the vegetated roofing industry.

RainScapes Rewards Rebates Program in Montgomery, MD offers qualified residential and commercial vegetated roofs tax rebate of $10/sf.

Baltimore Stormwater Fee Credit offers rebates for reducing impervious surface.

Blue Water Baltimore Green Roof Incentive offers $2/sf and covers up to 50% of total cost of project.

Green Roof Permit Program in Chicago, IL allows for density bonus and accelerated building permit.

Green Roof Tax Credit Philadelphia, PA, provides businesses a rebate of 50% for project cost up to $100,000.

Stormwater Management Incentives Program (SMIP) and the Greened Acre Retrofit Program (GARP) Philadelphia, PA offer stormwater management grants to non-residential property owners, and contractors.

Onondaga County’s Green Improvement Fund (GIF) Syracuse, NY has provided nearly $9 million in funding to local green infrastructure projects on private property

Green Infrastructure Grant program in NYC offers a grant program for private property owners in combined sewer areas of New York City. The minimum requirement is to manage 1″ of stormwater runoff from the contributing impervious area.

Green Roof Tax Abatement Program, New York, NY, offers rebate of $4.50/sf up to $100,000 per project.

Green Roof Rebate Program in Washington, DC: provides base funding of $10/sf, and up to $15/sf in targeted sub-watersheds.

RiverSmart in Washington DC provides reduction in stormwater fees and property taxes.

Green Infrastructure Partnership Program in Milwaukee, WI offers $5/sf for approved vegetated roofs.

Stormwater Credit Program in Minneapolis, MN includes vegetated roofs for stormwater utility discount of up to 100%.

Green Roof Credit Program in Nashville, TN offers up to $10/sf of green roof installed.
Stormwater Management Credit for Green Roofs in Devens, MA vegetated roofs may reduce size of stormwater management systems, save land and money.

Clean River Rewards Incentive and Discount (CRID) Program in Portland, OR provides property owners with the opportunity to earn a discount on their monthly stormwater utility charge by treating stormwater runoff onsite. Discounts are available to property owners based on the extent and effectiveness of on-site stormwater management practices that control flow rate, pollution, and disposal.

Density Bonus Incentive in Seattle, WA allows downtown commercial, residential, and mixed-use developments which gain LEED Silver or higher certification to build to a greater height and/or floor area than would normally be permitted.

Green Factor Program in Seattle, WA requires 30 percent of a parcel in the Neighborhood Commercial Zone to be either vegetated or functionally equivalent to a vegetated area.

Downtown Density Bonus Program, Austin, TX allows buildings with vegetated roof greater floor area than would normally be permitted.

Green Roof Loan Program in Cincinnati, OH offers $5 million in low-interest loans to property owners – residential, commercial, or industrial— for the design and construction of green roofs with an option to incorporate on-ground stormwater controls.

Stormwater Management Tax Credit in Anne Arundel County, MD offers 10% of the cost of the material and installation of an approved stormwater management practice, limited to $10,000.00.

Green Roof Rebate in Palo Alto, CA provides $1.50 per square foot for the installation of a vegetated roof to a maximum of $1,000 per single-family residential property and $10,000 for commercial/industrial and multi-family residential properties.

The Green Building Ordinance in San Francisco, CA sets standards for stormwater runoff and allows for expedited permits for green buildings.

Contact us for more info.

11 Sep 2017
Green infrastructure offers climate resilience in urban environments.

How vegetated roofs alleviate impact of climate change

Vegetated roofs, otherwise known as green roofs, are a key part of infrastructure resilience in an era of extreme heat events and more frequent and intense downpours.

Below are 4 ways vegetated roofs can have an immediate impact to improve resilience:


1. Help manage localized flooding

Vegetated roofs absorb rainfall, and help prevent water from overwhelming stormwater sewers and flooding streets or basements.  This reduces damage to infrastructure and property. They also reduce the volume of stormwater that flows into streams and rivers and thus protect local watersheds.


Vegetated roofs help mitigate urban heat island effect cooling the building, surrounding air and improving human health and comfort.

Vegetated roofs help mitigate urban heat island effect cooling the building, surrounding air and improving human health and comfort.

2. Help reduce urban heat island 

Vegetated roofs are a natural cover for rooftops that would otherwise absorb and retain heat.  Vegetated roofs mitigates air pollution levels an remove heat from the air through evapotranspiration. On hot days, vegetated roofs, reduce temperatures of the roof surface, and the surrounding air, improving human health and comfort.



Vegetated roof reduces the heat flux through the roof.

Vegetated roof reduces the heat flux through the roof.

3. Help lower building energy demands 

By shading the surface of the building, the vegetated roof is reducing the heat flux through the roof and reducing the indoor temperatures and demands on air conditioning.





Vegetated roofs delay peak flow and reduce pumping and treatment demands for municipalities.

Vegetated roofs delay peak flow and reduce pumping and treatment demands for municipalities.

4. Help save money managing water

Vegetated roofs retain and detain rainwater, delaying peak flow into sewer systems which helps reduce pumping and treatment demands for municipalities.


15 Aug 2017
Birds eye view of the vegetated roof on Mastery Cramer Hill Elementary.
Architectural rendering of Cramer Hill Elementary School in Camden, New Jersey designed by Blackney Hayes Architects.

Mastery’s first newly constructed school, Cramer Hill Elementary utilizes the latest approaches in construction technology.

CAMDEN, NEW JERSEY, UNITED STATES — The start of the new school year will be a fresh start, in more ways than one, for the Camden community that the new Mastery Cramer Hill Elementary school will serve.

“This brand new, safe and beautiful facility is one step in the right direction offering a world class education to Camden kids,” says Joseph Ferguson, Chief Operations Officer, Mastery Charter.

“That first day of school, what will really matter to me is that students and parents take pride in the school that was designed and built with them in mind. I want them to take ownership and truly believe this is a place where they can learn, and grow.”

World Class Education for Camden Kids

The city of Camden suffers extremes of poverty, and is reported to have among the nation’s highest violent crime rates. Many kids are in schools that are historically lower performing – in the bottom 10 per cent statewide – some in classrooms with no windows and no natural light.

Happy second-graders at one of Mastery's 24 schools in Philadelphia and Camden.

So impressed with their approach to education, talk show host Oprah Winfrey generously donated $1 million to the Mastery Charter organization.

Come September that will change for up to 750 local students who will attend the new school on East State and River Streets. Ferguson says that when students arrive at their new school, he wants them to “experience joy and great instruction.”

Cutting Edge Approach to Education and Technology

The vegetated roof, a high performing StormCap™ system, will be part of the learning as it is visible from classrooms on two levels. “In the construction of this new facility, the green roof presented a very economical and environmentally friendly stormwater solution,” says Ferguson. “It also provides an educational opportunity. Our teachers are excited and are looking forward to program the space in the future. We want students to be able to appreciate it. We want it to be part of the science program, by explaining why we have it, how it works, and how it helps the environment.”

Panorama photo of the construction of the Mastery Cramer Hill Elementary School vegetated roof.

Architects Kevin Blackney and Troy Hill of Blackney Hayes Architects designed the building. They say the green roof was proposed early in the design process to help with storm water management, and also as a learning tool. “This is Mastery’s first newly constructed school and in keeping with their cutting edge approach to education and technology, they thought it was important to utilize the latest approaches in construction technology,” said Troy Hill. “The green roof technology also gives the teachers the opportunity to use its function and maintenance to supplement their curriculum.”

The vegetated roof and pervious parking reduce runoff and manage stormwater on-site helping keep the local waterways clean. “Like most projects in urban environments with aging infrastructure, the storm sewer in the area is “combined” with the sanitary sewer flows,” explained engineer Charles Chelotti. “During heavy rainfall events, this combined system discharges directly to the local waterways and rivers. For this specific project, although there was net reduction in impervious coverage from the pre-existing condition, it was still necessary to reduce the impact to the “combined” system in the area, some of which may be over 100 years old.”

In addition to superior stormwater management, the vegetated roof offers other benefits for the building and the environment such as cooling the building, prolonging the lifespan of the roof itself, providing natural habitat and reducing the urban heat island effect. Also, research shows that biophilic design has direct advantages to students and teachers as views of natural landscapes from classrooms benefit academic achievement and behavior.

Workers unroll the sedum blanket onto the growing medium.

A team of workers from Ganter Contractors install the nearly 3000 square feet of vegetated roof in less than one day.

Ferguson, who is overseeing the construction of Mastery’s brand new building, is excited, too.

In mid-July under the blazing sun, Ferguson was present to watch workers from Ganter Contractors install the nearly 3000 square feet of vegetated roof in less than one day. “It looked very organized and straightforward. The team knew exactly what they were doing and I was very impressed with how efficient the installation happened.”

With school just around the corner, the team continues to work hard on the finishing touches to welcome new, eager students who will learn to love to learn.

About Mastery Charter Cramer Hill 
Mastery Charter operates 24 schools in the cities of Philadelphia and Camden. Cramer Hill Elementary is their first newly constructed school and will welcome up to 750 students and their families from kindergarten through 8th grade. From music to art to field trips – students will get a well-rounded education. Mastery schools are a special place where children experience the joy of learning in a safe, positive environment with a focus on 5 core values: respect, responsibility, hard work, teamwork and kindness.

StormCap pre vegetated roof systemAbout the Vegetated Roof System 
Innovative and easy to install, this green roof system is enhanced by the Urbanscape® Needled Hydro Mineral Blanket to maximize stormwater retention and keep weight down. The vegetated roof system uses pre-grown mats, engineered growing medium and high performing base layers loosely laid on a Sika Sarnafil roofing membrane making a more reliable roof.

StormCap™ vegetated system has superior water retention properties.
This green roof is customizable and contributes to 8 additional LEED points in the following credit categories:
• SS – Site Development Protect or Restore Habitat; Open Space; Rainwater Management; and, Heat Island Reduction
• EA – Optimize Energy Performance
• MR – Environmental Production Declarations
• EQ – Thermal Comfort; Acoustic Performance


Contact us with about your green roof project. We can help design and supply the right system for your building and location. Please contact us by email info@stormwatercaptureco.com or call 855-786-7626.

01 Feb 2017

The most notable development to date in vegetated roofing is the production of the needled mineral hydro blanket – a non-petroleum and formaldehyde-free alternative.

Knauf’s innovative needling manufacturing process provides dimensional stability without use of chemical binders.  The needled hydro blanket is formed by mechanical interconnection of pure mineral fibers.Needled Mineral Hydro Blanket

This process forms a structurally stable, lightweight and porous material with longer fibers that maintains excellent water holding properties. It is consistently hydrophilic, even after various weather cycles throughout the year. Up to 90% of the material retains rainwater. When wet, the majority of the retained water is easily available for the plants uptake.

The water absorption characteristics are not affected over time as nothing rinses away and will remain the same throughout the lifetime of the products.

The Needled Mineral Hydro Blanket is ideal for vegetated roofs, as it:

  • can supplement, or in some cases replace, heavy growing media
  • can act as a water reservoir and support plant health
  • achieves greater LEED credits
  • performs exceptionally and reliably as a rooftop stormwater management tool over the lifespan of the vegetated roof

Needled Mineral Hydro Cubes and Hydro Flocks

hydro cubesThe above needled, binderless, mineral wool also comes in the form of small hydro cubes (about 0.7 cubed) or hydro flocks (0.1-0.7 inch pieces) to mix with traditional growing media.

This is an innovative method of  improveing traditional growing media. Cubes and flocks contribute to better soil structure, water holding capacity and aeration of growing media. The retained rainwater inside the hydro cubes or hydro flocks is easily available for plant uptake, improving plant survivability. Cubes and flocks are specially recommended for patios, terraces and home gardening.


01 Dec 2016

Many remember the Eastern United States flooding of June 2006, a widespread flood that affected numerous watersheds and communities from North Carolina to upstate New York, causing millions of dollars in damages and taking 16 lives.

In the Federal Triangle, two metro stations were flooded and several federal buildings such as the National Archives, the Internal Revenue Service, the Department of Justice and several Smithsonian museums were forced to temporarily close.


In response to severe weather events such as the 2006 flood, District Department of Energy and Environment (DOEE) prepared and recently released the Climate Ready DC Plan which identifies 77 actions to reduce risks to infrastructure and its citizens. Among other things, the plan aims to make “100% of District waterways fishable and swimmable by 2032″. No small feat.

One goal is to “Relieve pressure on stormwater infrastructure and reduce long-term flood risk” with a target of capturing 75% of rainwater on-site for filtration or reuse. The first on its action list for stormwater management is the creation of two million additional square feet of green roofs by 2032. Such actions will “help prevent runoff from ruining river water quality and destroying plant and animal habitats”.

Mayor Vincent Gray’s ambitious vision is for Washington to become the” healthiest, greenest, and most livable city in the United States”. In achieving these goals, Washington “will be a model of innovative policies and practices that improve quality of life and economic opportunity”.

It is am important and grand plan. Let’s not only wish them luck but let’s work together to make it happen.

Photos credits: Sierra Club