
6 minute read
A Building for All Seasons
A BUILDING FOR ALL SEASONS

“Un Toit Vert” takes green standards to new heights
By Erin Ruddy
Located in the Quebec City eco-district of Estimauville, a six-storey apartment building stands among the eco-friendly structures built to push the boundaries of today’s sustainable standards. Called “Un Toit Vert” for a reason, the 70-unit residence offers adaptable, affordable rental housing geared at lower income families in an eco-friendly structure that was geometrically designed to optimize each unit’s supply of natural light.
With its flora-filled rooftop and sun-splashed courtyard, the property offers no shortage of outdoor green space. But what makes the building really stand out are the components you don’t necessarily see—like the airtight envelope designed with Québec City’s harsh climate in mind. “It’s a snowy, cold city, and the humidity is high,” says Frédéric Allard, Vice President of Constructions Richard Arsenault and general contractor at Un Toit Vert. “These extreme conditions aren’t always easy to work with.” Managed by the community housing technical group, Action-Habitation, Un Toit Vert features a living rooftop landscaped for resident enjoyment. Hardly a new concept, green roof systems have been delivering well-known benefits for years. They absorb rainwater, provide added insulation, create a habitat for wildlife and help to lower urban air temperatures in high density environments. Design-wise they can be simple or elaborate, consisting of low-maintenance herb gardens or lush, park-like spaces requiring permanent irrigation systems. It all depends on the strength and size of the roof structure and the level of maintenance building owners are prepared to invest.
At Un Toit Vert, the green roof is far from modest. This investment was all part of a master plan by the developer to achieve LEED Multifamily Midrise certification and Novoclimat status. Novoclimat is a certification program offered in Quebec that promises lower energy bills and healthier indoor air quality thanks to superior insulation, energy-efficient systems, and ultraefficient windows and doors. It is estimated that a Novoclimat home can save owners and occupants 20 per cent on energy costs compared to a house that complies with the Québec Construction Code.
To achieve the Novoclimat status, a multiple-unit residence must be heated by electricity, natural gas or residual forest biomass. Better temperature control is achieved through electronic thermostats, a mechanical ventilation heat recovery system and superior insulation.
At Un Toit Vert, the energy-efficient windows have argon filling, double-glazing and two low-emissivity coatings. The central ERV (Energy Recovery Ventilator) provides fresh air to units while an electric heating system, including baseboard heaters controlled by thermostats, keeps tenants warm. The building exterior is girded by semi-rigid insulation board to prevent thermal bridging of the steel framing.
Because of these features, Allard says, “Un Toit Vert has a really good envelope with an R-value of 27.”
The pursuit of LEED To achieve LEED Multifamily Midrise certification, builders amass points by installing energy-saving features that contribute to the reduction of annual energy use by at least six per cent compared with the baseline building performance set by ASHRAE 90.1. LEED points at Un Toit Vert were gained from the building’s central energy recovery ventilation system, as well as the green rooftop in the “heat island reduction” category. Heat islands in urban areas are caused by human activity and building density; they are known to diminish in the presence of vegetation.
Overall, Allard says the Un Toit Vert team is aiming for energy cost reductions of 25 per cent in comparison with the ASHRAE 90.1 reference, an accomplishment that will establish a new benchmark for energy-efficient building design.
Addressing thermal bridging To find a way to limit the risk of condensation, improve thermal comfort, and reduce energy loss throughout the structure, the designers needed to minimize thermal bridging between the building’s exterior balconies and conditioned interior slabs.
CIME Consultants Inc., the structural engineering firm for Un Toit Vert, specified the use of Isokorb load-bearing structural
- Frédéric Allard, Vice President, Constructions Richard Arsenault Inc.
thermal breaks, a component Allard had some prior experience with. According to Allard, the modules were selected because they contain a graphite-enhanced, expanded polystyrene block, which is less than 2 per cent as conductive as concrete. Additional energy savings are derived from the module’s stainless steel rebar, which is one-third as conductive as its carbon steel equivalent.
As Allard explains, the structural thermal break is aligned with the building envelope insulation layer, and positioned between each balcony and floor slab. Rebar projecting from both sides of the structural thermal break is cast into the interior slab and exterior balcony in a conventional manner, providing continuous insulation while supporting loads equivalent to a conventional pour-through slab.
A total of 67 apartment balconies, plus a balcony projecting from a community room, were fitted with structural thermal breaks. “Because it’s a public project, every cost was watched,” he said. “Un Toit Vert will help low-income people and give families a nice apartment to call home.”
Balcony-based thermal breaks Installing the thermal breaks involved attaching and extending rebar from the thermal break insulation modules to the rebar on the interior floor and balcony slabs, a process Gabriel Lévesque, steel foreman from Les Ferrailleurs du Québec Inc., says wasn’t all that difficult.
The process began with the concrete being poured onto the balcony slabs, then onto the interior slabs using different formulations. Lévesque notes that when the breaks are properly secured, “they don’t move” as the concrete is being poured. In total, 68 thermallybroken balconies were installed, spanning 343 linear metres.
Although it is still too early to gauge the precise energy savings derived from balcony-based thermal breaks, the Un Toit Vert team is anticipating good results. Meanwhile, occupants are enjoying a modern, eco-friendly place to call home.

Image: TERGOS Architecture & Construction
An Urban Oasis

Celebrated for more than just its green roof, Un Toit Vert has numerous ecologically-friendly features. For starters, the L-shaped volume of the building defines a central courtyard with optimal solar orientation. This volume makes it possible to maximize natural sunlight for a majority of dwellings. Other key features: • About 40% of the units have opposite windows at each end to allow natural ventilation; • Local, healthy, VOC-free and recycled materials were brought to the fore; • High performance centralized mechanical systems were installed; • A rainwater recovery system was integrated to supply community toilets, water outdoor plants, and clean the parking lot and residents’ vehicles.
What is Ecoquartier D’Estimauville? Located just minutes from Parliament Hill and Old Quebec City, Ecoquartier D’Estimauville is an innovative new neighbourhood where ecology and sustainability are the central focus. The community aims to reconcile density and quality of life by offering residents alternative modes of transportation, more ecologically friendly infrastructures and buildings, and a dynamic neighbourhood where residents can enjoy a full range of goods and services within walking distance.
