By Klaas Rodenburg
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Net Zero prototype for Habitat for Humanity brings fresh ideas for affordable housing
The Habitat Net Zero Prototype was developed as a collaborative project supplying a social, innovative, and affordable housing option to urban infill developments. This project was constructed as a pilot, allowing all parties involved in its development a chance to further refine and reflect upon strategies that were implemented to supply Edmonton’s Habitat for Humanity with its first net-zero home.
The project explored the collaborative development of a precast concrete housing unit that would be manufactured by Lafarge and donated to Habitat for Humanity as a prototype on an Edmonton infill site. Inspired by the unique properties of precast concrete construction, an innovative design was sought to reinterpret and challenge Habitat’s current construction layouts, including a lofty ambition of attaining net-zero status.
Helping Families in Need
In Edmonton, Habitat for Humanity builds more than 100 homes each year for families in need. These homes are built with donated funds, materials, and labour while eligible families provide 500 hours of “sweat equity” to be used as a down payment. Mortgages never exceed 25% of a family’s income, making them affordable.
Although Net Zero performance [meaning the duplex will generate as much energy as it uses] incurs extra capital costs for a hybrid geothermal/solar heating system and solar photovoltaic system to supply electricity to the homes, it significantly reduces monthly utility costs. This savings will partially offset the higher mortgage payments required to pay for the extra equipment. Thus, the initial investment will pay for itself many times over during the life of the building.
Thinking Outside the “Wooden” Box
What started with a simple lunchtime conversation between the team involved soon grew into a vehicle for innovative thinking about high-performance buildings. Lafarge wanted to prove that precast concrete is a viable alternative to the traditional wood- frame house. Habitat for Humanity had a standard plan for a duplex home – 1,060 sq. ft. on each side – that they can build on single lots or small infill communities at a very economical price. That is where Stantec’s design team started.
By adopting a standard model, it was possible for our team to compare prototypes by capital cost and performance throughout the life cycle of the homes. The design team decided to explore the full potential of concrete. The fluid nature of concrete and its ability to record the shape and texture of the precast forms allowed us to explore a wide range of alternatives to standard bed liners. This eliminated the need for vinyl siding on the outside or drywall on the inside, which reduced the cost and construction waste.
Modular wall panels gave us the opportunity to create a modern aesthetic with an exterior design that can be integrated into any community. At the same time, the modular wall panels offered sustainable features such as durability, living exterior walls, a “cap” for solar panels, and enough structural strength to house a green roof, although that option was not pursued for this project. Meanwhile, the ultra-high performance of the foam sandwiched between two layers of concrete provided an excellent exterior envelope.
Using an existing habitat site as a theoretical test fit, the Habitat Net Zero Prototype was developed to respect existing site constraints, typical habitat floor plans, and city development regulations. Precast concrete panels also had to be developed in a manner that they could be easily fabricated and altered within Lafarge’s standard form liners and pouring beds.
Once these structural and dimensional limitations were understood, the moulding and manipulation of existing plans could take shape. While the footprint and orientation of the units were to remain fixed, the units were manipulated slightly to provide private covered entrances and second-floor projections, allowing each unit to have its own identity responding to site, solar, and abutting landscape conditions.
The method in which the insulated precast panels are constructed and assembled creates an uninterrupted layer of insulation generating a superior level of thermal performance. Load bearing and non-load bearing exterior wall panels vary in thickness from 14” to 17” in thickness but both sections include 8” thick layers of continuous insulation.
Throughout the development of the Habitat Net Zero Prototype, sustainable systems where designed to be incorporated allowing the duplex units to achieve zero net energy on an annual basis. Geothermal, solar, and their accompanying mechanical systems have been examined and engineered for future inclusion which will help the project achieve a net-zero energy status upon their installation.
Economies of Scale
The lessons learned from this prototype will allow Lafarge and Stantec to develop a modular approach to constructing homes and multi-family residential buildings. The ability to produce repeatable, high-performance, precast modules on an industrial scale will significantly reduce the capital costs for homes, thus making sustainable home ownership attainable for more and more families throughout the world.
- Architect Stantec Architecture
Builder Habitat For Humanity
Mechanical Design Vital Engineering
Structural Engineer Kassian Dyck and Associates
Klaas Rodenburg MA, CET, LEED® AP is with Stantec in Calgary.