3 minute read
‘Floating in the Clouds’
Perched on the hillside of Whistler Mountain—one of North America’s top ski resorts—the 20,000 sq. ft. Kadenwood residence complies with stringent energy efficiency and seismic requirements. Its footprint is a four-sided polygon with sweeping views of coastal mountains and alpine lakes. The four-story ski-in/ski-out structure features access to the ski slopes 50 ft. below and three floors of year-round residential accommodations.
The building is a study in concrete cantilevers reminiscent of Frank Lloyd Wright’s Falling Water. “We wanted to cantilever the top two floors over the ski slopes and toward the views, so that when in the house you felt you were floating in the clouds,” explains senior technologist Eric Pettit of the Vancouver, B.C. architecture firm Openspace. Canadian building codes encouraged the use of structural thermal breaks to mitigate thermal bridging, explains Pettit. With the BC Energy Step Code, the building would have to include them to meet the high energy performance target.
TRANSFERRING LOADS BUT NOT HEAT
Cantilevers impart high rotational and shear forces, especially in the mountains of Western Canada due to the district’s snow loads of 176 psf. The designers needed cantilevered structures that could not only carry those loads but also meet the seismic requirements of the region.
“The whole structure is concrete— from the basement to the roof,” says concrete contractor Graham Roberge of Alpen Construction, a subcontractor of Bradner Homes Ltd. The project used about 2,616 cubic yards of concrete and a million pounds of steel reinforcement.
Given the high thermal conductivity of concrete and steel and its high surface area exposed to Whistler’s winters, the design team needed to mitigate thermal bridging and its unwanted effects.
INSULATE & SUPPORT
Designers specified four types of structural thermal breaks. For the balcony and roof elements, the team specified Schöck Isokorb® concrete-to-concrete modules. Each 3.3-ft. module consists of a block of rigid insulation penetrated by stainless steel rebar, which ties into the rebar of the interior slab and the cantilevered balcony. The insulation separating the interior and exterior slabs, together with stainless steel rebar, reduces heat loss at the penetration by up to 90%, according to the manufacturer. These modules are interspersed with different Isokorb® concrete-to-concrete thermal break modules that transfer horizontal earthquake forces.
Above several windows, the architects incorporated concrete “brows” that overhang a short distance similar to a sunshade. For these small cantilevers, the design team specified Isokorb® concrete-to-concrete thermal breaks for slab edges. The stainless steel rebar penetrating the insulation block ties into the interior slab rebar. On the exterior side, the rebar forms into a loop to support the small cantilever.
The fourth Isokorb® thermal break used connects concrete to steel at the steel balcony that cantilevers from the concrete structure over the entry area. The stainless steel rebar on the interior side of the module is wired into the floor slab rebar. Once cast in concrete, the exterior threaded side of each rod is bolted to steel
The Kadenwood Residence, Whistler, B.C., Canada (rendering).
Schöck North America
balcony beams using backing plates and high-strength stainless steel nuts.
Roberge estimates his crew installed about 1,000 linear feet of concreteto-concrete thermal breaks and 30 concrete-to-steel thermal breaks.
MOLD & CONDENSATION
The climate on Whistler Mountain averages 7-19° F in mid-winter, temperatures also fluctuate dramatically year-round, exacerbating problems of condensation and mold. “There is a constant freeze/ thaw cycle,” Pettit says. “Humidity in the house can start to condense on the cold surfaces and cause problems.”
Openspace began specifying structural thermal breaks in 2014 when designing another Whistler Mountain project. “We were trying to figure out how to hang heavy concrete cantilevers by designing our own bolt-on details. When we happened upon the Isokorb® products, I was excited,” Pettit says. “They were the perfect solution.”
Tracy Dacko is the former president of the New Jersey chapter of the Business Marketing Association. This article was originally published in Modern Contractor Solutions, Jan. ‘21.
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