Built Environment Strategies

All over the world, there is a significant opportunity to reduce CO2 emissions through efficiency improvements in our built environment:

  • Buildings are the largest source of energy consumption in the United States, accounting for 39% of primary energy use and 38% of national carbon emissions (1)
  • If the US were to retrofit its entire building stock, it could achieve efficiency gains up to 50% and reduce green house gas emissions by 25% (2)
  • The Center for American Progress has estimated that it would cost $500 billion over ten years to retrofit 40% of the nation’s building stock. They estimate that such an effort could generate 625,000 permanent fulltime jobs and save $32 billion to $64 billion a year in energy costs (3)
  • Cities contain 65 percent of the US population and account for 75% of national carbon emissions (4)


Figure 1: US Energy piechart showing breakdown of energy use in the building sector (Source: The Greenest Building: Quantifying the Environmental Value of Building Reuse)

Which is the better option, Renovating or Demolishing and Building anew?

There has been an ongoing debate in the architectural and construction industry: is it better to 1) scrap an old energy inefficient building and build from scratch a new energy-efficient one or to 2) rennovate? Now a new study proves that, in most cases, renovation is the lowest ecological footprint approach. The bulk of the ecological footprint is borne from the construction of the building – in excavating the raw materials, processing it and transporting it. The amount of savings that can be recouped is insufficient to make up for these losses. Many buildings already exist. Such retrofits are the low hanging fruit in a wider climate mitigation strategy. In addition to the environmental benefits, retrofits can also significantly reduce energy bills and create a new green job market.

Preservation Green Labs (A part of the National Trust for Historic Preservation)  is a Seattle-based NGO which advances research that explores the value that older buildings bring to their communities, and pioneers policy solutions that make it easier to reuse and green older and historic buildings. It seeks to minimize carbon impacts from the built environment through direct emissions reductions from older building retrofits and reuse, and to conserve character-rich and human-scale communities that attract people to more sustainable, urban living patterns.

In 2011, Preservation Green Labs released a groundbreaking study entitled The Greenest Building: Quantifying the Environmental Value of Building Reuse which provided the most comprehensive analysis to date of the potential environmental impact reductions associated with building reuse.

Up until this study, little was known about the climate change impacts of 1) reusing and retrofitting existing buildings vs 2) demolishing and replacing them with new construction. Using a Life Cycle Analysis (LCA) approach, the team compared the impacts of building reuse/rennovation/retrofitting with new construction over a timespan of 75 years. They can to the conclusion that building reuse almost always offers environmental savings over demolition and new construction.  In fact, the study concludes that it can take anywhere from 10 to 80 years for a new, energy-efficient building to negate the large climate change impacts created during the construction process. A caveat is that for retrofitted buildings to outperform new constructions, they must use efficient, low carbon building materials.

Indicators from four environmental impact categories were examined:

  1. climate change
  2. human health
  3. ecosystem quality
  4. resource depletion

Six different major types of building were studied:

  1. single-family home
  2. multifamily building
  3. commercial office
  4. urban village mixed-use building
  5. elementary school
  6. warehouse conversion

The study evaluated these buildings from four U.S. cities, chosen on the basis of representing different climate zones

  1. Portland
  2. Phoenix
  3. Chicago
  4. Atlanta

Key Findings

Building reuse almost always yields fewer environmental impacts than new construction when comparing buildings of similar size and functionality.(5)

The possible range of environmental savings of reuse over new construction vary between 4 and 46% comparing buildings with the same energy performance level. The environmental savings from building reuse varies widely depending on a number of factors including:

  • building type
  • location (climate conditions)
  • assumed level of energy efficiency

The one exception is the warehouse-to-multifamily conversion building category. The team concluded that it generates a 1 -6 percent greater environmental impact relative to new construction due to a combination of factors, including the amount and types of materials used in this project.


Figure 2: Summary of life cycle environmental impacts of building reuse, expressed as a percentage of new construction impacts. Base Case = average energy performance; Advanced Case = 30% more efficient than Base Case. (Source: The Greenest Building: Quantifying the Environmental Value of Building Reuse)

As can be seen, in almost every case, the reused building outperforms a new building construction. This study provides a strong impetus for renovating existing structures as the most effective way to make an environmental impact.

Carbon Footprint of a Home

In this Guardian article, the author writes about the carbon footprint of constructing a new 80 tonnes cottage with:

  • two bedrooms upstairs
  • two living rooms and a kitchen downstairs
  • one bathroom

It’s based on a study that the author was involved in for Historic Scotland. The study looked at the climate change implications over a 100 year period of various options for a traditional cottage in Dumfries:

  1. leave it as it is
  2. knock it down and build a new one to various different building codes
  3. refurbish

This analysis took into consideration:

  • the embodied emissions in the construction
  • maintenance as well as the energy used and generated by those living in the building

Option 1: Do Nothing

Unsurprisingly, the worst option by far was to do nothing and leave the old house leaking energy like a sieve.

Option 2: Knocking down and starting again

This worked out at about 80 tonnes CO2e whether the house was built to 2008 Scottish building regulations or to the much more stringent and expensive Code for Sustainable Homes Level 5 that demanded ‘carbon neutrality’. Here’s how that total broke down for the carbon-neutral option:

  • Walls 60%
  • Timber 14%
  • Pipework and drainage 9%
  • Floors 5%
  • Slate roof 5%
  • Photovoltaic panels 3%
  • Other 4%

Eighty tonnes is a lot and equivalent to:

  • five brand-new family cars
  • about six years of living for the average citizen in the UK
  • 24 economy-class trips to Hong Kong from London

But a house may last for a century or more, so the annual carbon cost is much less – and for all the new-build options, the up-front emissions from construction work were paid back by savings from better energy efficiency in 15–20 years.

Option 3: Rennovation

However, the winning option was the third option, to rennovate the old house, because the carbon investment of doing this was just eight tonnes CO2e. Even the highest-specification new-build could not catch up this advantage over the 100-year period. Once cost was taken into account, refurbishment became dramatically the most practical and attractive option, too.

The conclusion of this study? Investment in the very highest levels of energy-efficiency for new homes is, even at its best, an extremely costly way of saving carbon. Investing in improvements to existing homes is dramatically more cost-effective. NOTE: For homes in North America which primarily use wood and drywall construction, the mixtures and CO2e emissions will vary.

Analysis of Homebuilding in the Province of Llieda, Spain

An analysis from Spanish researchers is insightful in showing percentages of different materials in homes and rate of home building. The Spanish building sector consumes 50% of the natural resources, 40% of the energy and is responsible of 50% of the total wastes generated. (Arenas 2007).

Table 1. Main materials used in Catalonia (Spain), kg per inhabitable square meter of useful area and
percentage. Source: Cuchí, A. Arquitectura i sostenibilitat, 2005.


Figure 3 : Total mass of required materials for new housing in Lleida (inputs) and total generated emissions
of CO2 for producing the building materials per year (outputs, average 2000-2008). Source: own compilation
(IDESCAT 2008, Ministerio de Fomento 2008, Cuchí 2005).

The amount of required materials for building in the province of Lleida, Spain is shown in the above figure, where statistical data about the average of constructed area for housing among 2000 and 2008 and the weight of the main used materials per square meter of useful area of building have been taken into account.

  • Total annual tonnage of flow of material required to build homes in Lleida (both local and rest of it)  =3.25 millions tonnes/year or greater.
  • Most required material: aggregated = 1.75 million tonnes/year

Materials are stored in the anthroposphere in form of buildings. Aggregated material is mainly used in the structure of the building since is one of the components of concrete.

The output flow “wastes to the atmosphere” is also shown simultaneously in the figure above. Emissions of CO2 generated by all the processes necessary for the production of each building material required for new housing in Lleida every year are shown. The processes required for making possible the materials extraction imply the emissions of about 1 million tonnes of CO2 per year. The most emission intensive materials are:

  1. ceramic: 23% CO2e, 20% of total mass
  2. cement: 20% CO2e, 7% of total mass
  3. steel: 17% CO2e, 1% of total mass

Surprisingly, aggregates, though they form the majority of the mass only account for 1.5% CO2e. This is because of the high amount of energy required to process raw materials into ceramics, cement and steel.

Figure 4. Total stock and net addition to the stock of housing in Lleida every year (m2), and building stock
per capita (m2/cap). Source: Own compilation (Ministerio de Fomento 2008, Ministerio de Vivienda 2008,
IDESCAT 2008).

To determine the rate of new housing starts, it is first necessary to know the rate of accumulation of materials, and the time of residence in the stock (see figure above). The building stock in Lleida in 2008 was nearly 30 million square meters. From 2000 to 2008, the average net new addition to the existing stock of building was 1,240,000 m2 per year, an average of 5% of annual increase. This was higher than the increase of population , which averaged 1.9% annually. The building stock per capita reached the maximum of 70 m2 per inhabitant in 2007. Therefore the rate of accumulation of materials in the stock of building has been growing every year from 2001 to 2007, from 2.3 million tonnes of new materials added to the stock in 2001 to the 5.5 millions tonnes of materials in 2006. In 2007 and 2008 the rate of accumulation decreased, with 3.9 and 1.3 millions of tonnes, respectively.

(Source: Material flow analysis for reaching a sustainable model of the building sector, Villarreal, LR et al.)

A Retrofit Strategy for Communities

The above studies  for North American and European homes/buildings reach  the same conclusion, – that there is far less emissions associated with renovation than with tearing down and rebuilding a new modern, low ecological footprint home. We can see that the majority of carbon emissions occurs in the construction of a building rather than it’s usage.

This means that there is tremendous opportunity in the ecological home renovation market.

 Use of Appropriate Technology for Ecological Retrofit in Urban Communities 

At any one time, there are far more existing buildings than new housing starts. The market for ecological renovation is therefore substantial. To take advantage of this in developing country context, where the new building demands will be the greatest, we need to source innovative and affordable technologies.

This is where organizations like MIT CoLab, MIT’s community innovation lab can play major roles in developing appropriate technologies. CoLab is  a center for planning and development within the MIT Department of Urban Studies and Planning (DUSP). Its mandate is to assist excluded communities to develop and apply knowledge to:

  • deepen civic engagement
  • improve community practice
  • inform policy
  • mobilize community assets
  • generate shared wealth

CoLab’s principles are based upon community knowledge which can:

  • drive powerful innovation
  • make markets an arena for supporting social justice

CoLab facilitates the interchange of knowledge and resources between MIT and community organizations by engaging MIT students to be practitioners of this approach to community change and sustainability.

The MIT CoLab City Scale Retrofit Study

In 2010, CoLab researchers  Benjamin Brandin, Amy Stitely and Lorlene Hoyt released a study entitled City Scale Retrofits:Learning from Portland and Oakland as part of the Collaborative Thesis Project in which student researched a different post-industrial American city or set of cities and their use or potential use of stimulus funds for regenerating local economies.

The study is based upon the February 17, 2009 American Recovery and Reinvestment Act (ARRA) which injected $787 billion into the failing U.S. economy. According to the ARRA website, this stimulus was meant to:

  • Create new jobs and save existing ones,
  • Spur economic activity and invest in long-term growth, and
  • Foster accountability and transparency in government spending

The ARRA allocated over $20 billion to energy efficiency programs and represented the largest single federal investment in energy efficiency to date. ARRA money for energy efficiency was projected to weatherize 75% of all federal buildings and one million  private homes. In this way, ARRA was designed to help jumpstart the retrofit market. However, the question of how to sustain this market remains unanswered.

The purpose of this study was  to explore how municipal agencies and neighborhood institutions can work together to build a robust, sustainable retrofit market that delivers on the promises of:

  • lower carbon emissions
  • energy cost savings
  • development of local economy

The study did a case study of two city-scale retrofits programs in Portland, Oregon and Oakland, California comparing issues such as:

  • financial sustainability
  • scalability
  • equity

The team researched how to achieve equity in retrofit programs which can significantly reduce CO2 emissions at the same time that it creates significant jobs in local communities across the US. They concluded that equity must be at the forefront of any retrofit program, as broad community buy-in is the key to reaching scale.

One way to achieve buy-in is to proactively recruit program participants at the community level who have the most to gain in terms of jobs and utility-bill savings.

Partnerships are essential for broad participation, buy-in, and reaching scale. However, multi-stakeholder partnerships can be challenging to create and manage. Beyond technical concerns, partners must maintain good working relationships with one another. This is challenging, as partners represent different, often divergent, interests and have varying levels of social, human, economic, and political capacity.

Large-scale retrofit programs are characterized by these sustainable components:

  1. A mechanism to recycle the savings produced through the completion of energy-efficiency retrofits that can fund additional retrofits
  2. A means to creating and expanding access to quality jobs that can sustain middle-class families (high-road jobs)
  3. Targeted service delivery to a specific geographical area (city or region)where impact can be measured
  4. Prioritization of low-income residents in service delivery and jobs
  5. Democratic partnerships between local governments, community, business, and labor institutions

Study Conclusions

The team concluded that decisions about program structure and process lead to different outcomes in terms of which buildings get retrofitted, how they are retrofitted, and by whom.

Both Portland’s and Oakland’s programs aspire to the goals of the ARRA in terms of job creation and overall energy reduction:

  1. Portland’s program focuses more directly on the task of creating a new energy efficiency retrofit market, as the program is forwardlooking and scalable in its design. The Portland program’s CWA is also a solid mechanism for guaranteeing that retrofit jobs are good jobs that are accessed by disadvantaged workers.
  2. Oakland’s program appears to lack scalability and takes a lighter touch on regulating labor standards, the program is much more focused on delivering services to those who can least afford the investment.

The variation between these programs is due to many factors including:

  • leadership
  • city capacity
  • relationships
  • funding sources
  • local culture



(1) Energy Information Administration. Annual Energy Review. June 2009

(2) McKinsey & Co. Unlocking Energy Efficiency. 2009

(3) Hendricks, Bracken et al. Rebuilding America: a National Policy Framework for Investment in Energy Efficiency Retrofits. 2009

(4) ACEEE, “Energy Efficiency Program Options for Local Governments under the American Recovery and Reinvestment Act of 2009.”

(5) U.S. Environmental Protection Agency, Characterization of Building-Related Construction and Demolition Debris in the United States, available at http://www.epa.gov/osw/hazard/generation/sqg/c&drpt.pdf (1998.)