Can a Sustainable Home be Affordable?

By Klaas Rodenburg, Design Coordinator, Buildings Engineering (Edmonton, AB)

A rendering of the Stantec-designed
Net Zero Energy, pre-cast concrete
home.

Can a sustainable home be affordable? That is the question Stantec, Lafarge, and Habitat for Humanity set out to answer with the development of a NetZero energy duplex in Edmonton, Alberta. The duplex's innovative and integrative design, coupled with sustainable materials, will help create the ultimate energy-efficient precast concrete home. Construction on the duplex, the first of its kind in Canada, kicked off this fall.

Helping Families in Need

In Edmonton, Habitat for Humanity builds more than 100 homes each year for hard working families who need a hand up rather than a hand out in order to own a home. These homes are built with donated funds, materials, and labor 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.

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 pre-cast concrete is a viable alternative to the traditional wood frame houses. Habitat for Humanity had a standard plan for a duplex home – 1060 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.

Pre-cast concrete panels at the Lafarge
plant in Edmonton. Photo courtesy of
Lafarge

By adopting a standard model, it was possible for our team to directly compare prototypes in terms of 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.

Going Mod

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 for the harsh Edmonton climate that can vary from -300 C to +300 C (-220 F to 860 F) Energy models showed that the air-tight, R36 walls will achieve an EnerGuide 86 rating, which makes a NetZero energy target attainable.

Although NetZero performance 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.

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 efficiently 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.