Two installers on rooftop installing growing media on a snowy wintery day.

Installing Green Roofs at 20 Degrees

Construction schedule and handoff deadlines sometimes push green roofs towards seasonal freezeouts.

Many think of winter as the last time of year you would choose to install a green roof. However, with the proper planning, this season of hibernation and dormancy can yield a great result in spring.

Benefits of Winter Installation

Green roofs installed on mild winter days can benefit from the seasonal timing. Like perennial plants on the ground, all green roofs experience cycles of growth, flowering, and dormancy. During the summer, the plants spend their energy flowering. In autumn, plants divert more energy to root establishment and the sedum plants begin their process of dormancy and energy conservation to ensure their long-term survival.

While fall, spring or an early mild summer can be great times to install a green roof, winter installs will be equally successful as long as some key factors are considered.

The Arcade Sunshine green roof in January. Sedums in winter dormancy lose their flowers and change colour to creat a beautiful living carpet of reds, browns and deep purples.

CASE STUDY

December Green Roof Installation of Arcade Sunshine Condos 

Stormwater Capture Co provided material and install assistance for a 20,000 sf green roof on Arcade Sunshine Condos, an adapted textile mill and new building structures, in Washington, DC. Phase 1 and Phase 2 of the green roof sections were installed in December – a year apart. While the first phase saw milder winter days in the mid 40’s, the second phase saw mornings starting in the teens and topping out in the mid 30’s.  Green roofs in winter dormancy lose their flowers and change colour, creating a beautiful landscape of reds, browns, and deep purples. Coniferous sedum plants retreat to form a dense mat of glossy and fleshy leaves, while the leaves of deciduous sedum species completely fall off.

Green Roof System: Extensive StormCap Green Roof

Size: 20,000 sf

Phase 1 installation: Oct-Dec 2018

Phase 2 installation: December 17-20 2019

Tips for long term performance

  • Keep an eye on the daily and weekly weather forecast. An 18 degree dawn staging can yield above freezing temps by mid-morning.  For example, Phase 2 of the Arcade Sunshine saw average morning temperatures of 18 degrees fahrenheit at 6 a.m. then heated up to around 38 degrees fahrenheit by noon.
  • Base layers can be installed as long as they are pliable. Filter fabric and retention layer components need to be kept dry and from freezing on the roll. If saturated, they will not thaw easily. However, if there is enough radiant heat from sunlight, these components can shed some superficial moisture and frost by laying them in the sun.
  • As some of these components are dark they will absorb heat which can make them easier to unroll and will evaporate some morning frost.
  • Growing media can be provided in bulk or in super sacks (1.5cy landscape totes). If the media is kept in large hoppers or piles its mass can keep everything but the outer layer from freezing solid well into below freezing temperatures. It is important to move smaller and install media sacks quickly otherwise they can become frozen solid and difficult to work and grade. Radiant heat from a cold but sunny day, helps loosen the media further on the roof to allow for grading and planting.

Sedum Mats Pre-Grown Outdoors Acclimatize Best

  • Sedum mats pre-grown outdoors in a similar climate acclimatize best. On the east coast, mat harvesters will likely close down after new year through March as the ground freezes binding the sedum mats to the ground making harvest impossible. We can coordinate with you to schedule a harvest (and possible short term cool storage) until site conditions and delivery make sense.
  • Pre-cultivated mats should have a minimum of 80 per cent coverage upon installation and should be grown on the farm for 12-18 months to insure a healthy root base and reduce the possibility of erosion of growing media.
  • Ensure vegetation is established upon installation; avoid cuttings or installing plugs in frozen media. During this time of year it’s not worth the time and effort as many cuttings or plugs will dry out completely reducing coverage drastically.
  • If cutting or plugs are used then planting should wait until spring. Base layers and media can still be installed if the conditions allow. A protection fleece should be installed and secured to make sure weed seed banks or wind scour of media is kept to a minimum.

Long Term Survival

Diverse species and sedum selection will better ensure probability of long term survival. Our standard mat option includes many drought and cold tolerant species. We can work with you to provide the best plug or mat options for your specific roof, climate, and design intent.

Foot Traffic and Irrigation

Keep foot traffic over frost-covered plants to a minimum as this will rupture the cellular structure of dormant plants. Consequently, they can suffer disease or die off.

As plants wake out of dormancy in spring, temporary irrigation is important to promote growth. Depending on the climate, irrigate in mid-March or April to get the plants off to a good start but do not overwater.

Contact us with questions or for a quote on green roof systems with installation and maintenance assistance (virtual or on-site). We hope to have the opportunity to work with you this winter!

 

Ready to Design or Install a Green Roof? Contact us!

Transform any rooftop, whether industrial, commerical of residential, into a useful, green space. Stormwater Capture Co is a one-stop-shop for green roof systems and technical support.  We supply a range of  systems from lightweight and biodiverse, to detention green roofs.  We have custom green roofs that meet specific stormwater management and biodiversity goals. Contact us to transform your roof. Email or call (855) 786-7626 for stormwater calculations specific to your project.

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As a Purple-Roof partner, Stormwater Capture Co has access to the latest green roof stormwater test data and related innovative hydrologic modeling tool. Email or call (855) 786-7626 for stormwater calculations specific to your project.

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