We just approved the 20th Thousand Home Challenge project! Congratulations to Ruth von Goeler and Kelly Slough of Northampton, MA. They participated in National Grid’s Deep Energy Retrofit pilot in 2012. Their OPTION B threshold was 13,071 kWh (OPTION B inputs - fossil fuel heat, 4 in household, 3,208 FFA, and 6,208 HDD (base 65). Andrew Webster of Coldham & Hartman Architects was the project manager.


Their annual energy for the post retrofit monitoring period was 8,136 kWh. Their 110-year-old home was previously insulated and had a relatively efficient heating system. As part of the retrofit they substantially increased the finished floor area and still achieved a 61% reduction in energy use from their baseline. 


Attached is a spreadsheet with data from our twenty completed projects. 


Interesting numbers, ranges, means, and comparisons!  I welcome your observations. What is most interesting from the attached spreadsheet?  Please provide suggestions for charts and graphs to tell the story of the 1000 Home Challenge projects to date.



6.9 kBtu/ Ft2:  Avg Energy Use Index (EUI)[2]; US National avg. 44.8 kBtu/ Ft2 (single family homes)

1.91 kWh/ Ft2: Avg. THC Whole House Energy Use; US National Avg.: 14.27 Ft2

(5) Net Zero or Better

(3) Also charge Electric Vehicles

1,709 kWh/year: Average Energy Use per Occupant

4,554 kWh Average project energy use; 31,389 US National Avg: 31,389 kWh/yr

8,108 kWh Average project Thousand Home Challenge threshold



(17) Homes have PV; (8 of 20) Projects met the Thousand Home Challenge without PV

(93 kW) Total installed PV Capacity (17 homes)



1869 Oldest home; 2008 Newest home

Year Built: (20%) 1850-1899; (25%) 1900-1930; (15%) 1931-1960; (30%) 1961-2000; (10%) 2001-2010

Correlation between indicators of energy performance and age: None

576 Ft2 Smallest home; 3,208 Ft2 Biggest single family home

2,271 Ft2 Average house size (per household)

1.73 Occupants: Average household size

(18) Single-family homes; (2) Duplexes

[1] Energy use is site energy, total household energy; house size is finished floor area (FFA)


[2] This is an average from the 20 projects, not the average energy use for the total square feet of all projects


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  • I must say, I'm not a fan of EUI as an energy performance metric (for residential buildings, at least), because it rewards larger houses, and doesn't penalize larger aggregate absolute energy consumption.  Energy consumption per house or per occupant are better metrics, in my mind.
    I would also like to see a greater differentiation made between energy consumption and on-site energy generation.  Though from a carbon emissions standpoint, grid (fossil fuel derived) energy consumption reduction through renewable on-site generation is equivalent to reduction through conservation, so I see the logic.  But still. Not using energy, and using energy generated on-site are not the same thing.
    Maybe one thing to add to the spreadsheet or graphs could be the carbon emissions from the homes, along with that of the typical US home?

    Thanks for all that you do.  Great to see the THC Home Energy Pros page lively again!

    • RE: Your suggestion re Conveying Carbon Emission Reductions

      We have carbon emissions embedded in the Thousand Home Challenge application (based on national averages), so that could be tracked. Even if it is full of assumptions, it would help to convey that projects that meet the THC thresholds achieve a substantial reduction of carbon emissions regardless of the energy sources they choose. 

      Here is a comparison of carbon emissions from hypothetical projects. These emissions are calculated from PG&E emission factors. Their electricity is not as carbon intensive as the national average.3668614980?profile=original

    • Congratulations Linda! 20 projects is really great, and their energy performance is stellar. I assume that since you are sharing this, that the attached data are open for use by others? I've just finished aggregating DER performance across the U.S. from available case studies, and I might want to include these (some already are, of course). As for carbon emissions, I've derived carbon emissions factors for delivered electricity by U.S. state, based upon the US eGRID 2009 data (attached here, in case you're interested). While not exactly up-to-date (i.e., 2013) and not technically perfect in terms of grid structure, these values provide a much more nuanced and valuable metric in terms of carbon emissions, as they may actually direct project teams in different regions to retrofit differently. Anyways, well done on all this! 


    • Hello, Brennan!

      I am also very interested in what you find from aggregating DER performance across the U.S.  Performance data is going to be key to the general public's evaluation of this level of retrofit.  It is exciting to see such a rapidly growing body of published performance data and analysis!

      We (BSC) recently finished a report for Building America that analyzed data from the National Grid DER Pilot Program (2009-2012).   This Pilot yielded 42 DER projects (37 comprehensive retrofits, 5 partial DERs).  As far as energy use, we focused on what the building used.  In other words, we want to know how low the retrofit measures were able to get the energy use and we were not interested in how much any on-site generation facilities produced (not that producing energy on site isn't interesting, but on-site generation is not the same thing as building - and building occupant! -  performance).   As Linda experienced with these THC projects, it was difficult to find the actual use for buildings with PV given that the utility data is, for the most part, net use.  In other cases, the utility data is fraught with apparent attempts to reconcile estimated reads and a hugely changed energy use profile.  Some projects did not have sufficient full occupancy since completing the project.  Some folks just didn't respond to requests (contractual obligations relative to the generous financial incentives from National Grid) for information.  In the end, we were able to get usable post-retrofit energy use data for 29 projects. 

      I haven't had a chance to compare these projects in detail to the THC projects (there's a small overlap of projects) except to note that the THC projects kicked rumpus even relative to the amazing National Grid DER projects (it's only partly a difference of comparing gross use to net use)!

      The Building America report on the National Grid DER Pilot has been approved for publication but I do not see that it has been posted yet.  The report is titled "Performance Results for Massachusetts & Rhode Island DER Pilot Community".   I know we included tables of data so I think this should provide some projects to add to your aggregation study.



    • Ken, can you send me a copy of the report (bdless@lbl.gov)? I would love to review it. I'm not sure I can include the data points in my summary (as we're nearly finished writing the report), though I've already used what was provided in your prior summary of the pilot homes, as well as the 7 Cold climate projects summarized by BSC (can't remember if you're author or not?). I will definitely add your paper as a pre-pub reference, at the very least. Thanks for reaching out and I look forward to hearing from you and learning more about the project. As we get things finalized, I can also send you a copy of our paper.



    • Brennan, you can find the report here: http://www.buildingscience.com/documents/bareports/ba-1401-performa...



    • Thank you Ken, I'll read this with much interest.

    • Brennan -

      Always great to her from you. I would like to learn more about what you have found out from your aggregation of US DER case study performance. If you find projects that appear to meet the 1000 Home Challenge please send them our way. 

      The data I posted is public - fine to use or disseminate, though I request that you contact me to make sure that there is no misunderstanding about any of our categories, and that you have the latest version. I am working on an update that I should post within a week.

      One of the challenges of posting source energy or carbon emissions is that some of our projects do not have separately metered PV production. They just have net energy use. In some cases it is reported and recorded, but only on an annual basis, and the reporting year may not match our monitoring year. In other cases there was no metering installed to track PV performance. In addition, I have not tracked energy performance by energy source, though we have that data in the project application and actual project documentation. I could flag the projects that are all electric. Even so, not knowing the breakout between PV production, PV exported, electricity consumption from the grid and electricity used from the PV array would render an analysis of carbon emissions inaccurate.


      Most of our 1000 home challenge project contacts place a very high value on learning and sharing so they would be open to providing additional info if a 3rd party was interested in digging deeper.

    • Chris - 

      I share your concerns about using EUI as a metric. Any metric that is based on square footage of living space favors bigger buildings and penalizes smaller buildings. 

      I envision that we need a constellation of metrics to tell the story of a home's or an initiative's energy performance. It was only recently that I worked the THC OPTION B allowance backwards to see what the range of EUI would be for different climates, house sizes, and occupancy. 

      OPTION B of the 1000 Home Challenge generates a threshold that balances a number of inputs, and only uses finished floor area in order to estimate shell surface area (five sides). Below is a graphs that I find interesting. Hopefully, as a result, the OPTION B allowance meets the objective of being difficult to achieve across the full range of North American housing stock - ideally not favoring warm climates, cold climates, big homes, small homes, old homes, new homes, energy hogs or energy misers, homes serviced by low carbon electricity, or homes serviced by hydro. 


    • The Option B criteria themselves do an excellent (heroic, beautiful, gold-standard -- what other superlatives can I think of?) job at controlling for all the factors you cite, normalizing the difficulty for homes having different occupancies, behaviors, climate zones, heating types, etc. But then in the end to subvert all that innovative, clear thinking by comparing performance using EUI -- seems strange.  I understand the rationale -- it's a commonly-cited and broadly-understood metric. But then again, hey, whatever it takes; if EUI motivates and engages people and is not used in the certification process itself (but only after the fact), I'm all for it.  

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