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Multiple Roofing Assemblies Present Retrofit Challenge Energy and Waste Reduction Goals Shape Component Choice
March, 2008
By Tom Shreeve
The Sun Life Assurance Company of Canada Building at 227 King Street South in Waterloo, Ontario, is an imposing landmark with a low-rise building envelope and associated tower rising some 225 feet above grade. It houses the Canadian head offices of Sun Life Assurance. The original building was constructed in 1912, with numerous additions being constructed until 1986, some of which filled in and joined previously stand-alone buildings.
The roofing assemblies on the 29 different roof levels of the building range from 4-ply roofing systems to single ply roofing systems, from conventional to inverted. (A conventional roof is one where the insulation is below the roofing membrane, whereas the inverted system is one where the insulation is exterior to the roofing membrane.)
The well-kept grounds, complete with sprinkler systems and very limited access points for a large complex, posed a number of unique challenges when parts of the existing roofing assembly were scheduled for replacement as part of the ongoing overall building maintenance program.
SURVEY SUPPORTS LONG-TERM MAINTENANCE AND CAPITAL PLAN
Trace Molson of Bentall Property Services (Ontario) Ltd. interfaces with the owner/user of the facility to ensure that the building is continually operating efficiently, and, as part of the ongoing maintenance plan, Bentall had commissioned an independent roofing survey to confirm current conditions and assemblies.
Priorities were developed based on the expected useful service life, building use and the assembly content. For example, the roof on the tower contained a phenolic insulation, which can cause severe deterioration on steel deck substrates when moisture is present. Since this area was past its useful service life, this became one of the roofs designated for replacement, along with the three terrace roofs of the tower upper floor.
The survey provided projections on the remaining service life of the many types and levels of roof assemblies to support long-term planning and budgeting. This included an examination of insulation requirements and drainage issues.
Upgrading insulation on the roofing assembly at the time of roof replacement is an opportunity to enhance the efficiency of a major component of the building envelope with minimal costs and maximum benefits into future years. Bentall and the owner's commitment to energy efficiency also played a key role in this particular component.
Bentall and Sun Life's commitment to reduction of waste played a key role in the design parameters as well. The decision to use lightweight insulating concrete is one example.
LIGHTWEIGHT CONCRETE, MODIFIED MEMBRANES OFFER FLEXIBILITY
The lightweight concrete system, itself, will be reusable in the next roofing replacement; only the membrane component of the roofing assembly will have to be remediated. This will result in huge cost savings and minimal impact on disposal costs and landfill capacity. Reduced labour costs and reduced time to complete the work are among other advantages that provide the spinoff benefit of reduced impact on the building occupants.
Positive drainage will reduce the amount of standing water on the roof areas. The lightweight concrete systems are set to accommodate the available heights of the specific roof areas, taking into account heights of adjacent glazing components, siding heights etc.
Modified membrane roofs were chosen as a low-odour solution that offered the flexibility of being torched in place over the new lightweight concrete substrates with the use of cold adhesives in sensitive areas around fan intakes etc. This minimized the impact to the workforce within the building, which would have experienced odour issues during the installation of a standard 4-ply asphalt conventional system. Additionally, the white finished membrane is reflective and reduces solar heat gain on the roofing assembly and within the building.
CONSTRUCTION PRACTICES MINIMIZE DISRUPTION
In undertaking the tower roof, the insulation blocks that form part of the lightweight insulating concrete assembly and membrane were hoisted to the roof. The lightweight concrete was piped and pumped to the roof from the batching equipment below - since the contractor had experience in replacement projects that required pumping concrete as high as 450 feet, all the mixing and batching of product could be contained to the set-up area at grade, away from building intakes etc.
The three corner balcony roof areas, one level down from the tower roof, were completed at the same time to take advantage of the set-up. These balcony roof areas featured patio stones covering the entire surface to create a terrace for the adjacent offices, and approximately 3,300 stones were removed through the building via the elevators, with cooperation and assistance from Bentall and Sun Life.
All remaining roofing debris from the balcony roof areas was brought up to the main roof and hoisted down the exterior of the building to the set-up area. Had these balcony areas been completed at a later stage, there would have been more disruption to the owner's workforce caused by the removal of the old assembly and associated dirt and debris through the building.
SUSTAINABLE OUTCOMES
On some of the lower levels, the design and existing specific site conditions again allowed for the use of lightweight insulating concrete. Thermal values were increased, and a slope to drain system was installed, reducing and eliminating standing water from the subject roof areas.
Design considerations - such as existing perimeter parapet heights among other features - underlay the decision to remain with an inverted system in the perimeter of the tower sections of roofing slated for replacement. Modified membranes were applied to a new overlay of densdeck on the existing steel deck. The existing insulation and ballasting components were reused, with an additional layer of new insulation installed, doubling the previous R-value on the roof areas.
Keith Major, Senior Vice President, Property Management with Bentall reports that the roofing assemblies installed met objectives for energy savings and waste reduction. Remaining replacement projects, as they occur, are expected to follow the practices put in place in the completed areas.
Tom Shreeve, B.Tech (Bldg.Sc.), is with the Re-Roofing Division at Semple-Gooder Roofing, the contractor for the Sun Life complex retrofit. He can be reached at tshreeve@semplegooder.com. Keith Major can be reached at kmajor@bentall.com.
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