Cars, appliances, and televisions have long carried a “window sticker” that cites performance data. Is it time for new homes to carry something similar that addresses sustainability?
Homes have a collection of systems, some of which have these performance labels, but most homes do not. Is it possible to create one for the home itself, and would it be useful for home buyers?
First, it is important to outline what constitutes a sustainable house. The Australian Government’s ESD Design Guide (2007) defines it as “using, conserving and enhancing the community’s resources so that ecological processes, on which life depends, are maintained.”
Building industry stakeholders have more specific ideas, with requirements for energy, greenhouse gasses, and water performance. As Suzanne Tombourou, executive officer of the Australian Sustainable Built Environment Council, has noted, the implementation of these ideas “would allow the sustainability approach to be broadened beyond ‘low carbon’ homes to ‘low impact’ homes, giving potential buyers a much clearer picture of a building’s environmental performance and lifetime running costs.”
Building industry stakeholders also stated that they wanted requirements harmonised “across Australia so that assessment, implementation and compliance were uniform across the nation.”
Other stakeholders might opt for additional or different measurements, such as energy source, energy embodied in materials, amount of waste generated in construction and over time, durability of materials, resilience, adaptability, land use and siting, and so on. However, a comprehensive label could be cumbersome in practice.
“At this point there has also been very limited uptake of rating schemes that benchmark housing across a wide range of sustainability indicators,” wrote Dr Stephen White, ASBEC’s Sustainable Housing Task Group chair, CSIRO’s Energy for Buildings manager, and program leader for ‘Engaged Communities’ at the Low Carbon Living Cooperative Research Centre.
A variety of rating systems already exist, with a focus on different elements of building design and performance, such as indoor air quality, universal design, and so on. Presumably, those benchmarks could be combined to give the homebuyer a more comprehensive picture.
One important question, according to White, is whether multiple elements of sustainability should be considered in a single scheme, or separately.
“On the one hand, including all elements in one rating may dilute the attention required for individual elements,” he said. “On the other hand, multiple schemes to cover each element may become complex and create rating fatigue.”
Here’s an example of a window sticker from Postgreen Homes, a builder in the US:
The energy data for this sticker comes from HERS, the Home Energy Rating System, which uses construction specifications to estimate energy consumption. After the house is built, a certified rater performs a blower door test, duct leakage test, combustion analysis, and infrared camera inspection for heat loss.
Is that enough information for a homeowner or homebuyer? What about seeing performance data for the average year’s coldest day, hottest day, and average day? Obviously this idea requires that data be regionally optimized to be accurate, as local conditions have an impact on both house performance and the sustainability of available resources.
Yet, White noted, “it is yet to be seen if it’s possible to have a single one-size-fits-all rating system for sustainable housing.”
As for cost, does a sustainable home have to cost more than a standard home? A “window sticker” can also show that the adoption of more sustainable features makes sense, as studies show that sustainable homes do not necessarily cost more than those built to code minimum, and will be cheaper to run.
According to White, a Sustainability House study that compared about 4.5 million alternative house designs (each dot in the graph below representing a compliant design) showed that an energy efficient home can cost less to build than the “deemed to comply” design.
However, noted White, the designer must have the flexibility to design for optimal energy efficiency.
“If a fixed design is provided to the designer with the instruction to ‘make it compliant’, then the designer loses freedom to make appropriate trade-offs and is forced just to add compliance features (e.g. insulation, double glazing etc), with resulting increase in cost,” he said. “The key learning is that flexible rating schemes allow the construction industry to find the best solutions.”
While many metrics are easy to measure, the real wild card in the whole scheme is those who wind up living in the houses.
“While schemes that focus on house construction quality are important, it appears that additional work is required to focus on occupant behaviour,” White said.