B.C. building insulates interior slabs from balconies with thermal breaks

Figure 1: The structural thermal break detailed here provides structural support and insulation to minimize heat transfer through thermal bridges penetrating the building envelope. Tension and shear bars running through the insulation block tie into the steel reinforcement bars of the building’s interior slab and cantilevered exterior penetrations.
Figure 1: The structural thermal break detailed here provides structural support and insulation to minimize heat transfer through thermal bridges penetrating the building envelope. Tension and shear bars running through the insulation block tie into the steel reinforcement bars of the building’s interior slab and cantilevered exterior penetrations.

Since British Columbia has a history of seismic activity, the design team also specified thermal break modules to provide lateral strength for earthquake load transfer in concrete balconies. They transfer horizontal shear parallel to the insulation layer as well as uplift forces. This type of break is used in addition to the linear connection models (Figures 1 and 2) mentioned earlier.

Totally, 1928 linear m (6325 ft) of structural thermal breaks were installed, equating to 5.5 m (18 ft) per balcony on average.

“All of the thermal breaks were placed on the slab formwork toward the end of laying the rebar for the slab. Concrete for the floor slabs and balconies was poured at the same time,” the engineer continues.

Co-ordination among the trades ensured the project’s success. Blair Marriott, senior superintendent of ITC Construction, says, “We organized site meetings with the sub-trades, particularly with shoring contractors to ensure they understood the proper load paths. The team commitment resulted in success.”

Figure 2: Illustrated here is a type of thermal break that serves as a shear force transfer element for column supported concrete balconies at 3 Civic Plaza, transferring vertical shear forces from concrete slabs with continuous bearing along the linear connection.
Figure 2: Illustrated here is a type of thermal break that serves as a shear force transfer element for column supported concrete balconies at 3 Civic Plaza, transferring vertical shear forces from concrete slabs with continuous bearing along the linear connection.

Thermal performance

According to the thermal break manufacturer, their modules can reduce heat loss through the balcony by up to 90 per cent.

They also increase the warmth of interior floors adjacent to the balconies by up to 19 C (34 F), and prevent condensation and subsequent mould formation adjacent to cold balcony penetrations.

As a result, structural thermal breaks can help comply with increasingly stringent building codes and expected thermal comfort levels.

Multiple energy-saving measures minimize costs and carbon emissions

As further energy enhancements, the structural engineer says, “In-slab hydronic radiant heating/cooling tubing mats distribute heating and cooling to all of the units. The energy originates from the City of Surrey District Energy System, and is distributed through the building in a continuous ambient hydronic loop. Dedicated heat recovery chillers extract the energy from the loop and transfer it to holding tanks until it is called again to heat or cool the units.” The geothermal district energy system serves most of Surrey city downtown and is expanding.

Figure 3: Insulation filler modules maintain the fire rating of concrete-to-concrete connections where transfer of forces is not required.
Figure 3: Insulation filler modules maintain the fire rating of concrete-to-concrete connections where transfer of forces is not required.

These energy measures at 3 Civic Plaza reduce capital and operating and maintenance costs and increase the building’s marketability.

The developers followed the 2012 British Columbia Building Code (BCBC) in the building’s design. The engineer adds, “The structural thermal breaks posed no problems in conforming with the code.”

Building codes in Canada set to require net-zero energy by 2030

Effective April 2019, the City of Surrey adopted the B.C. Energy Step Code, enacted to improve energy performance levels, and measure energy efficiency in all building systems including the airtightness of windows and walls, roofing, and mechanical equipment. The B.C. Energy Step Code will help reduce greenhouse gas (GHG) emissions and increase the energy performance and comfort of new buildings in Surrey. There is also a pan-Canadian effort by the National Energy Code of Canada for Buildings (NECB) to require all new buildings to be ‘net-zero energy ready’ by 2030.

This expected performance will require minimizing thermal bridging in structures, which would otherwise have a considerable impact.

Dritan Topuzi, PhD, P.Eng., PMP, LEED AP, is the product manager of Schöck North America. He is also an adjunct faculty member at Norwich University, Vermont. He received his PhD from the University of Waterloo in 2015. Topuzi is a member of the American Concrete Institute (ACI) and the Canadian Standards Association (CSA). He can be reached  via e-mail at dritan.topuzi@schock-na.com.

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