Mot-clé : Energy efficiency
In Quebec, residential, commercial and institutional buildings’ operation and maintenance is responsible for a significant share of the GHG emissions: 10.3 billion tons CO2 equivalent in 2007, accounting for 12.5% of overall emissions. 41% of these emissions come from the residential sector, mainly due to the use of fossil fuels for heating. The good news is that those emissions have been steadily declining since 1990, thanks to improvements in buildings’ energy efficiency and the transfer from fossil fuels to cleaner energy sources. Although gains from further improvements in energy efficiency are still possible, we now need to capitalize on the high potential offered by the communities’ development and patterns.
The efficiency of urban form
The current development pattern based mainly on single-family detached houses leads to enormous energy losses, as far as heating is concerned in particular. The type and characteristics of a housing unit can vastly impact its heating energy needs.
Average energy consumption for heating by housing unit category
|Housing unit category||Consumption (kWh/yr)||Floor space (m2)||Consumption by m2 (kWh/yr/m2)|
|Single detached||24 903||138||181|
|Single attached||15 375||113||136|
2008 data collection for Quebec, Office of Energy Efficiency of Canada
In fact, heating a single-family detached house requires on average 2.3 times more energy than an apartment, and 1.6 times more than a single-family attached house. There are two main reasons that explain these variations:
- Size: On average, a single-family detached house is 1.5 times the size of a typical apartment and 1.2 times the size of a single-family attached house.
- Energy efficiency of the housing unit pattern: due to its shape and location, a single-family detached house is more vulnerable to the elements than a single-family attached house or an apartment. Indeed, the latter benefit from the protection and the heat from adjacent units. This explains why a single-family detached house requires 1.5 times more energy than a similarly-sized apartment and 1.3 times more than a single-family attached house.
These differences cause higher GHG emissions for single-family detached houses that rely on fossil fuels for heating (hydro-electricity is very common in Quebec and emits very little GHG). In this case, emissions of a single-detached house are 3.84 tons of CO2 equivalent/unit/yr. This number falls down to 2.87 tons/unit/yr in a single-attached house and an apartment only accounts for 2.45 tons/unit/yr.
Besides, units tend to be underused as they always get bigger while households slowly shrink. This results in unnecessary heating of mostly unoccupied rooms.
Lifecycle, materials and construction
Operations and maintenance are not the only aspects of a building accountable for GHG emissions. Indeed, when we look at the ecological footprint of a building, we must consider its whole liftecycle from design to operation and maintenance, and even the way it might be reused or recycled. Construction of buildings and infrastructure is responsible for about 20% of neighborhood energy consumption and greenhouse gas emissions over a 50-year assumed lifespan. Buildings must be designed in order to capitalize on the characteristics of the site in which they will be set, considering for instance orientation, shade and insulation. This practice is called bioclimatic architecture, and it materializes through passive solar building design. Building materials choices (local when available, non-toxic, easily recyclable…) and construction wastes management must also be addressed. Taken all together these considerations can have an important impact on the GHG emissions of buildings.
Healthier and more comfortable buildings
Energy efficiency and GHG emissions are not the only factors to take into account: greater comfort through better building design, for example, is another benefit. Smartest use of available space, precise temperature control and healthy building materials are only a few of the improvements that fall into designing buildings according to stringent quality standards.
The building sector must take part in the development of sustainable communities. But these issues all have to be addressed in a global perspective. The improvements in energy efficiency have been considerable in the recent years. Even so, building type and location remain essential to an efficient strategy to lower GHG emissions.
-  Ministère du Développement durable, environnement et parcs (Québec), 2010. Québec 2009 inventory of greenhouse gas emissions and evolution since 1990. (in French) ↩
-  Office of Energy Efficiency of Canada, Comprehensive Energy Use Database Tables – Residential Sector, Quebec. ↩
-  Jonathan Norman et al., 2006, in Playbook for green buildings + neighborhoods – Construction impacts. ↩
Density, and notably residential density , is closely related to the issue of urban sprawl. Indeed, developing low-density neighborhoods implies to always set them a little farther on the outskirts, taking up large non-developed areas for a small number of residents.
Density and GHG emissions
The density of housing and activities has a significant impact on greenhouse gases emitted by a community, mainly because it determines the residents’ needs in motorized travel, especially by affecting the level of public transit services the community can sustain. Indeed, below a certain residential density, public transit becomes inefficient and very difficult to implement and/or pay for. Moreover, a dense environment encourages the use of active transportation. The difference in density between two neighborhoods can generate an important difference in GHG emissions. For example, a community with a density of 43 housing units per hectare would emit 38% less GHG through its transportation-related activities alone than one with a 3.6 units/ha density, and 14% less than another with a 21 units/ha density!
Density, synonym of efficiency
Increasing residential density not only reduces GHG emissions but also lowers travel distances and energy consumption. But the benefits of a denser living environment go beyond the transportation issue, as it also lowers overall energy consumption. A single two-story house will experience 20% higher energy losses on average than a semi-detached, and 50% more than an apartment.
Moreover, density offers municipalities the opportunity to save money, since higher densities result in significant reductions in public expenditures, particularly for major infrastructures, roads, police and education services. In Toronto, studies found that a more compact development of the region in the next 30 years would help lower the investments in buildings, transportation and public services (water and sewer pipes, etc.) by 10 to 16 billion dollars and the operating and maintenance costs by 2.1 to 4 billion dollars. Finally, compact living environments also increase businesses’ and local services’ viability and resilience.
Density, a misused concept. And yet…
Some people are reluctant to medium- to high-density environments for all kinds of reasons related to the quality of life which turn out to be unjustified most of the time. Residential density is far from being synonym for high-rise buildings! While ensuring a convenient density level, combining townhouses, duplex and triplex apartments can contribute to the making of pleasant, diversified and sustainable communities. In fact, when the concept of density is well implemented, it can be perfectly compatible with typical family needs like sufficient space, adequate privacy and green space. The quality and quantity of semi-private and public spaces make up for the sometimes smaller size of private spaces. In addition, such a lifestyle is also usually more economical for all.
Moreover, the benefits in terms of efficiency and profitability help dense environments offer residents a variety of services that are impossible to obtain in low-density environments. Parks, kindergartens, schools, businesses, public transit, leisure and cultural facilities… Compact communities make these services easily accessible and collectively affordable, for the benefit of all.
Solutions for our living environments
There are different mechanisms for action. Cities can do the following:
- Make the redevelopment of wastelands a priority.
- Make the zoning bylaw’s regulatory provisions on building height more flexible.
- Impose a minimum density and authorize the densification of existing neighborhoods.
- Restrict the urban boundary.
With a little creativity, there can be found many ways of increasing the density of existing neighborhoods without reducing the quality of life of current residents.
The EcoDensity project of the city of Vancouver is a good example of a practical application of these concepts. It encourages residents to build a second house in the backyard of their single family home by modifying their back-alley garage entrance. This initiative has also been called “Hidden Density”. Today, we can see a great variety of designs for these houses that are typically intended for aging parents or young adults.