Energy Use Over the Last Year In the ADU

In earlier posts, I shared how living in smaller spaces reduces per capita energy consumption, which was part of my motivation for living more compactly. Furthermore, after constructing an energy efficient ADU, Energy Trust of Oregon even gave me a $1,750 rebate for meeting Northwest ENERGY STAR standards and achieving a modeled Energy Performance Score of 35. 

Now that I've lived in the ADU for over a year, I wanted to share the actual energy bills, and compare them to the energy bills of the main house. Comparing the utility bills of the two dwellings will allow me to draw a few conclusions regarding the nuanced personal energy consumption virtues of living more compactly.

Both homes are heated by natural gas. The ADU is heated via a tankless water heater and in floor radiant hydronic heat. The main house, built in 1906 and recently weatherized, is heated through a conventional forced air heating system.

Below are the natural gas bills for the ADU and the main house, respectively. The ADU consumed 277.5 therms, and the main house consumed 930.4 therms. A "therm" is a unit of heat equal to 100,000 British thermal units.

The total therms used in the last year in the ADU

The total therms used in the last year in the main house

At only 277 therms, the ADU used only 29% as much energy as was used by the main house for heating!

That's very cool, but that's not the real story. 

The real story must include the total energy use divided by the number of occupants. The designed occupancy level is calculated by taking the number of bedrooms in the house, and adding one additional occupant. This designed occupancy level assumes that two adults are living in a 'master bedroom' together.

The ADU is a one bedroom dwelling designed for two people. And, in fact, that is exactly what happened in the ADU;  two people lived in the ADU for the full year. 

The main house is a four bedroom house, with a designed occupancy level of five people. However, in reality, the actual occupancy rates of the main house were lower than the designed occupancy level; the main house maintained an average of three occupants throughout the year. 

Interestingly, census data shows that the average national occupancy rate for homes larger than mine at 1,700 sq ft, is surprisingly low. The average occupancy rate for homes of 2,500 sq ft is actually only 2.59 occupants.

So, let's look at the therms used per capita for both the designed occupancy and the actual occupancy.

If the main house were occupied at the design occupancy rate, each ADU occupant would have used 75% as much energy as the average resident in the main house. Living in the Northwest ENERGY STAR certified ADU would have been 25% more energy efficient than living in the main house.

But, in reality, with only three occupants in the main house, the actual therms used per capita for heating and cooling in the ADU was still 138.75, but the actual therms used in the main house was 310.13. This means that by residing in the ADU, I used only 44% the amount of energy that the average occupant used in the main house. Living in the ADU has been, in reality, 56% more energy efficient than living in the main house.

These are significant data points. Here are the stories that these data points tell us:

#1) Building the new structure to Northwest ENERGY STAR standards resulted in building a very efficient building envelope and in choosing to use efficient heating systems.

#2) By living at the designed occupancy in the ADU, my partner and I each lived more energy efficiently. Building a smallish dwelling alone did not make the dwelling energy efficient. It was dwelling in a smaller footprint per capita that had the most substantial energy efficiency impact.

Said another way, if I lived alone in the ADU, and the main house was fully occupied at the design occupancy of five people, I would have actually used 50% more energy than the average resident in the main house.

#3) In smaller dwelling spaces like my 800 sq ft ADU, I was prone to live at the designed occupancy level of two. Conversely and representatively, the main house was prone not to be fully occupied (according to US Census data).

These last two points are a thinking person's fodder for a housing revolution.

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I'm also including my electrical bills from the last year for reference. Since neither the ADU nor the main house used electricity as the primary heat source (where the bulk of a home's energy is used), these data points are less relevant.

That said, indeed, the ADU was more efficient than the main house in terms of electric power consumption due to the types of appliances and light fixtures that were installed. But, one will still draw a similar conclusions that I have drawn above regarding designed and actual occupancy

Under actual occupancy rates, living in the ADU used 30% less electricity per capita than living in the main house.        Under designed occupancy rates, living in the ADU would've used 18% more electricity per capita than in the main house.

In terms of electricity, the ADU was more efficient under actual occupancy rates. But, if the main house was occupied by five people, the electricity use per capita in the main house would have actually been lower than in the ADU.

Electricity used in the last year in the ADU

Electricity used in the last year in the main house

Note the July spike in electricity use in the main house and the lack of a spike in July for the ADU.

The main house is set in direct sun, has R12 wall insulation, and has an AC unit.

The ADU is kept cool through deciduous tree shading, R33 wall insulation, and a ceiling fan. :)

Living Compactly

Live in under 400 sq ft./person. Live in a walkable community.

These principles are the ethical drivers that have informed my personal interest in ADUs. Making these two personal lifestyle choices will very likely decrease one's environmental impact significantly (without much concerted effort for the individual to be more 'green' or 'less consumptive').

My conclusions are based on findings that closely correlate personal energy and consumption impacts to residential locational and housing size.What follows in this post are selected infographics and text that help explain these recommendations.

For US residents that generally believe in climate change trends, and therefor understand the importance of reducing individual energy consumption, it is also important to understand that we owe it to the rest of the world to reduce our individual carbon impact. I am suggesting here, that living compactly is the easiest and probably the most substantial way that most of us can reduce our individual carbon, energy, and BTU footprint.

Tons of carbon dioxide emitted per capita in the US and globally

I'll clarify my opening prescription- living in under 400 sq ft. is an arbitrary residential square foot benchmark, not a numeric prescription. My intention is to convey that the smaller the residential footprint per person, the less the environmental impact. I've provided background data about living in smaller spaces in an earlier post. This post will focus more on residential location choices.

You can find more wonderful infographics that originate from the same report in my earlier post entitled Common Forms of Living Smaller. You can also watch a 1.5 hour Oregon DEQ presentation about the Residential Buildings: An Evaluation of Waste Prevention Practices Using Lifecycle Analysis report on EPA's website.

This quantitative analysis of residential construction types shows that in terms of residential housing types, housing size is the most significant variable in terms of ecosystem quality, human health, and energy consumption.

Urban Density

Urban density is an important factor to sustaining a vibrant urban, walkable community. The urban density in US cities is an average of 2,900 people/mile. Portland's average urban density is 3,507 people/sq mile. By comparison, New York city is 23,705 people/sq mile and Pheonix is 2,342 people/sq mile (based on 1990 Census data). My neighborhood has a density of 4,241 persons/sq mile, or 14 people per acre.

When a sufficient level of residential density is overlaid other critical aspects of urbanity, such as mixed zoning districts that include employment opportunities, readily accessible park networks, a variety of housing and transportation options, a region will significantly reduce its energy demand per capita.

Oregon had the foresight to create an urban growth boundary in 1977. This 30 year old policy, has resulted in a range of benefits that are becoming increasingly evident to urban planners and residents alike. The proactive, multi-jurisdicational, planning modality, appropriately reflects and manages the region's transportation, housing, and employment demands.

Portland's viable transportation alternatives and vibrant neighborhoods are a testament to the success of the urban growth boundary. A range of other unique urban planning policies and natural assets have helped make Portland walkable and community focused. While most, if not every, city in the US has seen a growth in total vehicle miles traveled from 1996-2008, averaging growth of 9% over that period, Portland's total vehicle miles traveled from 1996-2008 has dropped by 12%.

The following screen shots were taken from a presentation by Peter Calthorpe, Calthorpe Associates.

Walkability

Contrary to a popular assumption that transit is the most viable alternative to driving, using the following graphic, Peter Calthorpe explains that transit should be conceived as a third tier support mechanism for walking and biking. In the western, industrialized cities in Europe, transit is not the dominant form of transportation, nor is driving. The dominant form of transportation is actually walking and biking.

Cities have to focus first on making places that are walkable. Transit should be perceived as a way of extending the walk/bike domain. To accomplish this end, cities need to provide more mixed use, high density housing choices in a range of prices within given neighborhoods.

Hidden Personal Costs of Living in Sprawl

However, even if no active policy choices are made to adopt and adapt cities for future livability, the market will nonetheless steer builders, architects, developers, in this direction. The demand for exurban, large lot housing is going to slowly decline over this generation, and large lot exurban properties will be increasingly labeled as a liability.
 




Here's a couple personas (Dave and Karen) that exemplify common lifestyle differences between Dave, a resident in a single family detached house in a "conventional suburban development", compared to a Karen,  who lives in a multi-family building in a "transit oriented development", and the respective amount of energy (BTUs) that they use as a result of their transportation choices.

This data is based on a report called "Location Efficiency and Housing Type - Boiling it Down to BTUs," that was funded by the US EPA. This presentation from which these graphics were extracted is available on this HousingPolicy.org website.



Market Trends Towards Urban Revitalization

Solely allowing the free market to guide urbanization trends means that the urbanism trend will not be coordinated and managed as well as it could be, and will cause financial hardship for many homeowners and municipal governments.

Graphic from a report called Growing Cooler

Embracing Infill Housing Programs

ADU's are one of many programs that cities should actively adopt in order to to increase housing options in areas where there is sufficient housing demand. Currently, many communities do not allow ADUs. Moving forward, urban communities that are seeking to actively embrace an environmental ethic should seek to:

• Expand the range of allowable housing options and areas in which they may be built
• Revise policies that make these housing types impractical
• Consider ways to reduce the reliance on variances and expand "as of right" development opportunities

Recommendations from HousingPolicy.org

In the US, I think that we owe it to the rest of the world to reduce our energy consumption footprint. In the US, living compactly is a contrarian choice, but the dominant habitat that we observe and experience in the US when driving from one place to another is neither healthy for us nor sustainable.

But, individuals can make an active decision to live in a smaller space at home, to live more compactly within their community, and enjoy the financial and lifestyle freedom that these choices provide. Indeed, there are social and health benefits to living smaller, but perhaps the most compelling reason is the decreased transportation and decreased housing costs associated with this passively virtuous choice.