La Joie de Rosemont

Retrofit and Expansion of Former Medical Clinic Incorporates Structural Thermal Breaks to Create Energy Efficient Housing

A former medical centre at 5601 Bélanger Street East, Montreal, has been transformed into a 55-unit cooperative called the La Joie de Rosemont (The Joy of Rosemont) where roughly half the units in the rental building are designated as affordable housing.

Developed by the CDH Group and its partner, the Rosemont Housing Committee, the project was built to Novoclimat standards, the Québec-based program that sets energy-saving benchmarks for new residential construction and major renovations. As one measure, multi-storey structures incorporating balconies and cantilevered slabs that penetrate the building envelope must include structural thermal breaks.

Balconies both retrofitted and poured as new

“The Rosemont project combined the retrofit of the existing building with the addition of a reinforced concrete extension at the back,” explains Damien Soyez, Structural Engineer with Poincaré Experts-Conseils.

The retrofit was driven in part by health concerns as asbestos use was banned in Canada in December 2018. Interior and exterior partitions in the medical centre contained asbestos and had to be removed.

Starting in the Fall of 2019, the former Domus Médica health clinic was stripped down to its original concrete shell. Next, a 752 m² (8094 sq ft) reinforced concrete extension was added to the rear of the structure, doubling the footprint of the original building.

Work is now complete and the building is occupied. The retrofit portion spans three floors plus a basement garage, while the extension rises four floors above grade. Total gross floor area in the completed coop amounts to 5,536 m² (59,589 sq ft).

Fifteen steel balconies measuring 2.6 m (8 ft, 8 in.) long and 1.5 m (4 ft 10 in.) wide, were retrofitted to the façade of the former medical building (which previously had no balconies), while 27 reinforced concrete balconies were poured along with floor slabs in the new extension.

To prevent thermal bridging at the balconies and meet Novoclimat requirements, the structural engineers opted for Schöck Isokorb^® concrete-to-steel structural thermal breaks for the retrofit, and concrete-to-concrete structural thermal breaks for the new extension.

By reducing thermal bridging between the balconies and the interior slabs supporting them, structural thermal breaks reduce heat loss at the connections by up to 50 percent, reducing the need for tenants to raise thermostats—an expensive proposition in Montreal, where winters are notoriously long and cold. By preventing interior surfaces adjacent to balcony penetrations from becoming chilled and reaching dew point, the thermal breaks also prevent condensation and mould formation that could remain undetected for years before becoming visible, exposing the owner to liability and remediation costs.

Retrofitting of steel balconies using structural thermal breaks

Prior to anchoring concrete-to-steel thermal breaks into interior floor slabs of the existing structure to support steel balconies, General Contractor Devcor electronically scanned the building façade to locate existing rebar on each floor and avoid drilling through it.

Once scans and calibrations were completed, horizontal boreholes were drilled through the supporting outer concrete spandrel beam and into the interior slab to anchor the thermal break reinforcement bars. Each concrete-to-steel thermal break required four boreholes: two measuring 19 mm (3/4 in.) in diameter by 762 mm (30 in.) in length and two measuring 13 mm (1/2 in.) in diameter and 279 mm (11 in.) in length.

After drilling, saw cuts roughened the adhesion surface on the concrete where the thermal breaks would be placed. The boreholes were cleaned and injected with epoxy adhesive, and the tension and shear bars of the thermal breaks were carefully placed inside the boreholes. The epoxy produced “optimal adhesion between the thermal break reinforcement bars and the concrete,” explains Jérôme Paquet, Engineer and Project Manager for General Contractor, Devcor.

The Isokorb^® concrete-to-steel thermal breaks used are specifically designed to reduce thermal bridging on retrofitted steel balconies. Tension and shear force bars penetrating the insulation block transfer negative moments, positive shear forces and horizontal forces.

Waterproof sealant was applied to the thermal break surface areas contacting the existing concrete. A non-shrink grout was injected into the opening on top of the break. Finally, the new steel balconies were lifted and fastened to each thermal break with anchor bolts.  

Each retrofitted balcony is insulated and supported by five thermal breaks—one for each steel balcony support beam. The breaks were placed between the balcony beams and the spandrel beam on each floor girding the building’s circumference, reducing heat loss by up to 75 percent at the connection. 

Pouring of new concrete balconies incorporates structural thermal breaks 

Meanwhile in the building’s 752 sq m (8094 sq ft) extension, the 27 reinforced concrete balconies were constructed with concrete-to-concrete thermal breaks (Isokorb^® Type K/CEQ). The concrete for the interior and exterior slabs was poured on the same day. 

Concrete-to-concrete structural thermal breaks transfer bending moments and shear forces via stainless steel upper tension bars and bent shear bars that pass through rigid foam insulation modules and tie into rebar of the balcony and interior slab. As stainless steel is approximately one-third as conductive as carbon steel rebar and rigid foam insulation is approximately 98% less conductive than concrete, the thermal breaks reduce heat loss at the penetration by up to 90%, according to the manufacturer.

A Successful Transformation   

Novoclimat regulations cover more than balconies and reducing thermal bridging. Multi-unit buildings must be powered by natural gas, forest biomass fuel, or electricity, for example. Windows need to be ENERGY STAR qualified for the city’s climate zone; air conditioners must by ENERGY STAR qualified for energy efficiency. A mechanical ventilation heat recovery system drawing fresh air into the main rooms improves air quality. Superior air tightness is verified by leak detector test.

Mr. Paquet says that Rosemont successfully transformed an old medical clinic into Novoclimat-certified housing by deploying thermal breaks and other energy-saving measures, creating a more comfortable and efficient environment for its new occupants.