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April 3, 2009admin Comments OffMerchandise Lofts Building Green Roof Case Study Toronto, Ontario
Background
In 1910 Robert Simpson Co Ltd. constructed a five-storey, reinforced concrete and steel structure, which was used for wagon storage and as a harness shop. In 1916 an 11-storey mail-order building and warehouse was added at the south end of the complex. The final construction phase of the complex took place in 1930 when additions were made at the north and west sides.
Throughout the last decades of the 20th century numerous development plans for the then vacant Simpson’s building were put forth to the City of Toronto. However, each of the project plans fell through. In 1997, Cresford Development of Toronto introduced a plan to construct a new, mixed-use (residential, retail, and commercial) complex. As the plan incorporated more residential development into an area that had been a concern of the City for some time, it was approved for its development permit.
The building, now known as the Merchandise Building, consists of 504 loft residential units, 529 above-grade car parking spaces, 246 bicycle spaces, 4 loading bays, a 30,000-square-foot food store, and 35,300 square feet of retail and office space.There are nine styles of luxury condominiums ranging in size from 565 square feet to 1765 square feet, which are priced from $148,900 to $425,000 respectively. At street level the building features retail space including a major grocery store chain and a restaurant. A twelfth storey was added to the structure to make space for an indoor pool, party room, dining facilities, and an outside dipping pool.
The roof is landscaped with a prairie meadow growing in two green roof plots. The green roof proper is approximately 10,000 square feet and is surrounded by an additional 15,000 square feet of hard surface concrete pavers. The decision to install the green roof was made by the development in the final phases of the redevelopment project in order to maximize the area available for planting without needing to adjust the structural loading capacity of the building. The total redesign and regeneration of this 1,070,000-square-foot complex is believed to be the largest of its kind in North America.
Highlights
• Building Type: 12-storey, multi-use condominium complex
• Units: 504
• Typical Population: 500-800
• Location: 155 Dalhousie Street Toronto, Ontario
• Status: Renovations/conversion of complex completed in February 2000
• Cost of green roof retrofit: $200,000
• Area of green roof: 10,000 square feet of planting area 15,000 square feet of decorative concrete pavers
• Green roof type: Extensive
• Saturated weight: >30 lbs per cubic foot
• Developer: Cresford Development Inc.
• Architect: Paul Northgrave Northgrave Architect Inc.
• Landscape Architect: David Lieberman, David Lieberman Architects Terry McGlade, Perennial Gardens
Budget
The 10,000 square foot green roof and corresponding 15,000 square foot hard surface area was designed, supplied and installed for just over $200,000 (approximately $8.00-10.00 per square foot).
Allocation Expenditure
Landscape Design $10,000
Green Roof Materials (includes supply & install) $105,00
Plants (includes supply & install) $67,000
Irrigation $12,500
Ornamentals (galvanized steel planting structure) $8,000
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Total: $202,500
Structural Considerations
The original building was constructed of steel and concrete. The extra weight of the recreational facilities (a green roof, lap pool and sun terrace) would have been in excess of the roofs original loading capacity. In order for the existing building to withstand the additional weight, the entire roof was reinforced with steel girders.
It is very important to note that while the weight of the roof was a concern, the need for the steel girders was mostly due to the extra loading from the lap pool and not the green roof.
The saturated weight of the green roof is less than 30 pounds per cubic foot. In fact, the decision to use a green roof system, instead of traditional planter boxes, was made because of its low weight.
Installation and Technical Issues
The original plan for the roof was to create a container garden on top of a traditional roof. However, to increase the planting space available, the project developers commissioned a green roof after construction had begun and the roof had been installed.
The installation of the green roof on the Merchandise Lofts posed three major technical problems:
1. getting the materials (growing medium, plants, slabs, etc.) on to the roof of a 12-storey structure,
2. working in a construction site, and,
3. using a pre-existing roof as the base to build the green roof plots on.
The problem of getting the material to the roof was overcome with cranes that were already on the site for the building renovation. The landscape designers worked closely with the contractors to avoid conflicting schedules and avoided problems that might have occurred due to implementing the green roof during the major construction project. The designers of the roof had to overcome some issues with placement of the plots and plants due to the location of some building mechanical equipment that were installed on the original roof.
Green Roof Characteristics
Type and Warranty
The Merchandise Building green roof is an accessible extensive system that uses selected elements of Soprema’s Sopranature green roofing system. However, as it was placed on top of the original gravel-top roof, it incorporates many of the original roof features including membrane and flashing. The roof on which the green roof elements were placed upon holds a standard 10-year roof warranty. Selected elements of the green roof are warrantied, but as it is not a complete green roof system, there is no universal warranty. The plants were warrantied for one-year effective from the date of purchase.
Growing Medium
The growing medium used was a mixture of Soprema’s Sopraflor-X, which is designed specifically for extensive green roof systems, and “grow-bark” potting soil. Sopraflor-X is comprised of an unconsolidated mixture of organic matter and mineral aggregates with a particle size of 16 mm. Soprema claims its growing medium will provide optimal water retention, permeability, structural stability and density.The grow-bark potting soil is comprised of soil, peat, manure and compost.The mixture was selected for its light weight and ability to adhere to the plants in windy conditions.The growing medium was applied across the plots in varying depths (from two to eighteen-inches).
Plant Selection
The primary issue when selecting the plants and designing the green roof plan, was the excessive wind and sun exposure. The green roof is located on the roof of the twelfth storey and has southern exposure. Native species, such as grasses, that function well in extreme conditions were selected. The plants were also grown in ‘plug’ sizes that ensured firm roots in the shallow growing medium. 37 different species of native Ontario plants were included in the design. Examples of the selected species are: Switch Grass (Panicum Virgatum), Hairy Beardtongue (Penstemon hirsutus), Gray-headed Coneflower (Ratibida pinnata), Pale Purple Coneflower (Echinacea palida), Woodland Sunflower (Helianthus divaricatus), and Sedum (spurium red, Ewersii, sexangulare, kamtachaticum, spurium Album). The total budget for the plants was $67,000, which included their transport to the site and installation.
Irrigation & Drainage
Currently, the plants are irrigated through a drip irrigation system, which cost $12,500 to purchase and install. No specialized drainage system was installed for the Merchandise Building green roof. It is using the pre-existing drainage system from the traditional gravel roof.
Monitoring & Maintenance
No monitoring of the green roof has taken place or is planned. There have been no funds allocated for maintenance or replacement of lost plants. However, as the building will be governed by a condominium association, the decision to create a budget for future replanting, reproofing or repair may be made at a later date.
Benefits
The major benefit that the green roof offered the developer was the ability to create outdoor recreational space for future tenants with maximum green space and minimal hard surface coverage.While originally the roof was to be comprised of container gardens, the green roof’s low weight, allowed for the design of additional green space without creating the need to re-examine and make adjustments to the loading capacity of the roof.
The Merchandise Lofts gave the landscape designers the opportunity to experiment with new light-weight growing mediums and plant selection. Reviewed by Marty Lapedus.