Cedar Springs Residential Project
Cedar Springs Retirement Residence, Vancouver, BC
Structural thermal breaks prevent thermal bridging where cantilevered concrete balconies and eyebrows (shown here) penetrate the building envelope, averting heat loss and interior mold growth, while increasing occupant comfort.
Installation of Schöck Isokorb®
Tension bars running through the insulation block tie into the steel reinforcement bars of both the building’s interior slab and cantilevered exterior penetrations.
Structural Thermal Breaks in Vancouver
Help High-Rise Developer/Owner Meet Sustainability, Investment Goals
Benefiting the environment and bottom line
Vancouver, British Columbia–When building its 11-story, $23 million Cedar Springs Retirement Residence in North Vancouver to LEED Gold certification, Developer Pacific Arbour Retirement Communities (PARC) maximized the return on its investment in sustainability by employing conventional energy-saving measures plus—for the first time in Vancouver—structural thermal breaks to prevent heat loss through concrete balcony slabs.
“We build, own, and operate each and every facility. As opposed to some developers that simply build something and sell it, we live with the product,” explains PARC vice president of Development and Construction Russell Hobbs. “So, if we design something that’s efficient from a utilities-usage standpoint, that’s always helpful to us from an investment perspective. Long-term efficiencies are a big consideration for us.
“With Cedar Springs, we were trying for at least 25% energy savings through design elements like an insulated exterior wall system, shade-producing eyebrows, triple-glazed windows, and structural thermal breaks (STBs). Unique about STBs was that they allowed us to build an economically viable building using an inexpensive heating plant (electric-radiated baseboard heating units), only if we could do something to offset its use. Normally, people use heavy glazing everywhere for that offset, but that isn’t a particularly efficient building envelope. We wanted to do something different with an inexpensive energy system and a highly efficient, insulated building envelope. And we had a mandate to create a thermal break between the structure and the building envelope to minimize heat loss. STBs were part of that building envelope strategy.”
PARC Cedar Springs Director of Construction Bob Fritz adds, “Our focus was on the overall building envelope from a thermal point of view. The insulation is thicker than any of the other buildings we see going up in Vancouver. The STBs are designed to maintain that uniform insulating value of the exterior cladding.”
In justifying the use of STBs, Hobbs highlights the all-too-common building conundrum of thermal bridging, which typically occurs where concrete or steel cantilevered elements such as balconies, canopies and rooftop connections penetrate the otherwise insulated building envelope. Heat loss through these structures into exterior environments increases carbon emissions and energy costs, forms condensation and mold growth in cold interior recesses, and chills interior floors adjacent to balconies, all of which can be overcome by insulating the structures where they penetrate the building envelope.
Cedar Springs an ideal candidate for STBs
Cedar Springs proved an ideal candidate for STBs. The facility boasts 146 units or suites, many with cantilevered concrete eyebrows (shade-producing concrete slabs) and balconies. In addition, PARC was looking to achieve LEED Gold certification for Cedar Springs, a regulatory requirement in Vancouver for new construction, and attained it in June 2017.
An Isokorb® STB from Schöck North America is an engineered construction element the same approximate width as the building's exterior wall that creates a thermal break between the interior and exterior sides of these penetrations. It contains insulation and load-bearing components with rebar that is fully cast into the slab at the penetration.
The STBs reduce heat loss and carbon emissions at balcony penetrations by up to 90 percent at the penetration, and up to 14% for the building overall, contributing significantly to the project team's strategy in achieving LEED Gold certification.
Bob Fritz explains: “You need to look holistically when designing energy savings. There isn’t any one thing that makes or breaks a design. But the use of STBs gives you the possibility for greater flexibility in other areas, like the choice of an inexpensive heating plant. One of the secondary benefits of including STBs is the comfort level of the residents within the units. Without STBs, a cold area develops adjacent to projecting slabs for balconies or where shading eyebrows penetrate the exterior envelope. That’s a heat loss in the winter and heat infiltration in the summer. The area closest to the perimeter wall becomes less comfortable in the interior residence. The STBs prevent that heat transference, maintaining the uniform insulating value of the exterior cladding.”
According to Sophie Mercier, P Eng, and Director of Building Science West at Morrison Hershfield (the project’s building envelope consultant) and project principal on Cedar Springs, “The owner was very open to the use of Isokorb STBs. In fact, he was the one who made it part of the early stages of design. It was an important element of the overall energy strategy. When you look at the thermal efficiency of an envelope, even if it has exterior insulation, the amount of energy lost through balconies and eyebrows without those thermal breaks is significant.
"Depending on the wall assemblies and the architecture of the building, and how good or not your walls are, the heat lost through the slabs and slab extensions can be significant. With Cedar Springs, for example, there’s an eyebrow at every floor. Without the thermal breaks, the thermal performance for that building would have been very different. If the walls are good, then your slabs become your penalty, where most of the heat loss will happen. If you want to keep those elements, the thermal break becomes a really good solution.”
STBs broke new ground in Vancouver
Bob Fritz says, “In Vancouver and the greater area, people were unfamiliar with STBs when the project broke ground in 2011. There was a learning curve to get the local structural engineer and our architect more conversant with the technology. Schöck North America helped bring our design team up to speed on incorporating the STBs into the design. Since STBs were also new to our building trades, instruction was required on putting them into the forms and tying them in with the rebar.”
“Once we secured the actual installation date, the Schöck team of engineers personally supervised the installation."
He says, "Cedar Springs was probably the first project in the Vancouver area to use Isokorb® STBs, but we’ve designed them into subsequent projects including the Westerleigh Retirement Residence in West Vancouver and our current project in White Rock that’s scheduled to be completed in 2019. Other buildings in Vancouver now use it as well.”
Fritz points out that STB use could become widespread depending on the regulatory process and local building codes, particularly in helping structures meet LEED standards.
Besharat Friars Architects
Ventana Construction Corporation