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Concentration of CO2 in the Atmosphere

Transforming the Building Sector with Energy-Positive Homes

Rendering of the 85 homes at the Summit Oaks development at Village Hill in Northampton, MA. Photos courtesy of Transformations, Inc.

Rendering of the 85 homes at the Summit Oaks development at Village Hill in Northampton, MA. Photos courtesy of Transformations, Inc.

By R. Carter Scott

Buildings account for about 42% of the carbon emissions in the United States. The transportation sector uses another 25%. Why not use the building sector to drive down its emissions as well as those of the transportation sector?

With the concentration of carbon in the atmosphere surpassing 402 parts per million – and rising at more than 3 parts per million in the last year alone – our society needs to change, if we want to continue living on a planet that we have grown accustomed to.

Building homes that produce as much energy as they consume is not a difficult task. It has been done cost-effectively for eight years in New England. Building homes that also produce surplus energy for its occupants’ transportation needs is also not difficult. This has been done since 2012. The task at hand is to “scale up” the knowledge and practices, so that this is the standard practice everywhere.

California has mandated that zero energy be the standard for new residential construction by 2020 – the first in the nation to do so. In Massachusetts, we should follow their lead and have all new residential homes here built to the zero energy standards by 2025 – that would give us nine years to make the transition. Maybe some other New England states can join our efforts for 2025 such as Vermont or Connecticut. We can then set out to make zero energy the standard for 2030 for the rest of the country.

How does one build fossil-free, energy-positive homes in a cost-effective manner? The first part of the equation is technical. Many in the building industry have proven zero energy is fairly easy to do. Building Science Corporation has suggested some minimum standards for the shell: R-5 windows, R-10 basement slab, R-20 foundation walls, minimum R-40 above grade walls and minimum R-60 attic insulation. You then add a cost-effective hot water system such as the air-source heat pump water heater. The heating and cooling is easily done by air-source heat pumps. Ventilation systems can be as simple as a couple of quiet bathroom fans running continuously at low speeds, a heat recovery ventilator, which provides better energy performance than the bath-fans approach.

A home in Devens, MA that produces much more energy than the homeowners consume.

A home in Devens, MA that produces much more energy than the homeowners consume.

To get energy positive homes, one just has to add enough renewables on the roof to power the home and overproduce for other needs, such as vehicles. The key here is the ratio of the roof area to the floor area. A typical two-story, zero-energy home has a roof to floor area ratio of 0.30 to 0.33. To get homes producing enough energy for the transportation sector, one needs to have more roof space relative to the floor area. When the ratio gets into the 0.66 to 0.70 range, then you can solve for the carbon associated with the transportation sector. One can easily do this with a saltbox house with the larger roof area facing south or with a ranch with the longer dimension facing south. Homes have been built that produce over 10,000 kWh of excess energy in a year. This is enough energy to drive a typical electric car for 30,000 miles, year after year.

The 2015 International Energy Conservation Code (IECC) is currently under public review in Massachusetts. If adopted, this code will bring the Home Energy Rating System (HERS) index to 55 for a standard code-built home. For reference, the IECC 2006 code home was 100.

Over 150 communities in Massachusetts have adopted the stretch code since 2009. This voluntary code requires these communities to go further than the base energy code. The original stretch required energy use to be cut by 30% and carbon emissions 40% compared to buildings built to the base energy code.

Opportunity number 1: We have an opportunity to continue having the stretch code move us towards zero-energy homes. The current proposed residential stretch code simply makes the voluntary 2015 IECC base code’s option of scoring equal to or less than 55 mandatory. Homes already using this option would not see any additional requirements. Why not? Let’s work toward an additional “stretch” in the stretch code. The Department of Energy has a Zero Energy Ready program that is very well thought out. The jumping off point for adding renewables is in the very cost effective range of HERS 50. Let’s make the DOE Zero Energy Ready home program the stretch code for new homes.

Opportunity number 2: Then what’s next? Let’s plan a path to requiring all new homes in Massachusetts to get to zero energy by 2025. There is a proposal from Mindy Craig, principal of BluePoint Planning in California. She is the principal writer of the Path to Zero for California. It took about a year of stakeholder meetings and planning for California to create their eight year plan in 2011. The proposal is to do for Massachusetts what has been done in California, spend the time to get the stakeholders on the path together. Massachusetts could be the first cold climate state to require zero net energy for all new homes – an exciting time for changing the way homes are built in the time of climate change.

R. Carter Scott is President of Transformations, Inc., a developer and builder of zero-energy homes and communities and installer of residential and commercial solar systems. Carter is a member of Governor Baker’s Zero Net Energy Building (ZNEB) Advisory Council and has been building zero-energy and energy-positive homes since 2008. His email address is carter@transformations-inc.com. The company phone number is 978-772-1390.

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