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Zero Energy Design Binge

by Chad Ludeman on January 5, 2008 · 28 comments

in Design,energy modeling,Green Programs,inspiration

Zero Energy Design ImageOver the Christmas break I went on what I am now referring to as my “Zero Energy Design Binge.” I started thinking about the through wall air conditioner we are considering to handle the cooling demands for the home and thought it would be fantastic if there was a way to economically eliminate the cooling demand altogether via passive design. This thought quickly put me into research mode and when I couldn’t find anything in stock at my local Borders or B&N, I found an 800 page e-book on the subject from

While I normally don’t buy e-books if they are not immediately downloadable, I made an exception and the CD-ROM arrived just in time for Christmas break. The book consumed many hours over the break. While there is a ton of great info in the book, it became very evident very quickly why it was an e-book and not actually available in bookstores… Skipping over the 200 pages of political ranting helped cut down the time to read a bit.

The biggest thing in the book that caught my attention was the concept of a “Thermal Buffer Zone (TBZ)” or double shell envelope that could significantly reduce the cooling and heating demands if designed and built properly. Basically the idea is to build a double envelope on the North and South sides of the house as well as above and below the house. This would create TBZ around the interior shell of the house where air that is not conditioned but is milder than the outdoor air could freely circulate. See the image below for clarification.
ZED Double Enelope Diagram

The concept allows each envelope to be built economically without the need for extreme amounts of insulation and top of the line energy efficient windows. This is because having two smaller differences in atmosphere (outside – TBZ & TBZ – Interior shell) are more efficient than on large difference in atmosphere between the outside and inside of traditionally built houses.

The diagram above shows how the home would operate in the summer with cool air originating under the home, gaining heat and humidity as it rises and being exhausted out the top of the house. In the summer the TBZ could get up to 80 degrees or so when it is the hottest outside but it will still be cooler and less humid than the outside air.

In the winter the design functions differently. The South face of the house is actually encouraged to use as much single pane glass as possible in order to let in the most heat from the sun in the winter. The South side is on the right of the diagram above. The air on the South is warmed by the sun during the day, rises to the top and slowly falls to the North side of the building to warm the side of the house that is not getting direct sunlight. This air then cools and continues down under the house and flows naturally back to the South side where the process starts over again. Temperatures of 80 degrees or more in the TBZ have been recorded in houses of this design during the winter when snow is on the ground.

Modern Glass Garage Door ImageOne of the things that got me excited about this concept was the possibility of incorporating a glass garage door on the South side of the house on the ground floor. This had been investigated early on by ISA but thrown out due to thermal losses that would occur. With the TBZ design we could possibly incorporate it again and have a large atrium type space in the back that could be opened wide to the back yard when weather permitted.

To cut my story down a bit, we ultimately agreed that the TBZ design is interesting but should be shelved for a future project due to cost constraints on this project. Besides simply materials costs, there will most likely be added labor costs for throwing too many new ideas at our builder and subs at once. The design we have now is still very unique and extremely energy efficient compared to the average home and probably even the average LEED home.

Here is a list of some of the things I took away from the ZED book that may be applicable to our project. None are really groundbreaking but it helps to have a review again close to the end of the design process on passive design:

  1. Minimize or eliminate all windows on the West side of the house. This is not an issue for the 100K house but it is for the corner house that has a 40′ exposed wall facing West.
  2. Minimize the amount of windows on the North side of the house. We have a lot of glass there now and may be able to reduce while still letting in a lot of light.
  3. Radiant barriers are extremely important, especially on the roof, for keeping the house cool in the summer. Traditional insulation is not enough.
  4. Designing windows that open on the bottom of the North side of the house and on the top side of the South side will aid in passive cooling via breezes in the summer (especially at night). The windows at the bottom should be half the size of the windows at the top.
  5. Exterior shading is extremely important for the South side of the house and low-cost, permeable shading material may be able to shade the entire back yard in the summer if designed correctly.
  6. Interior, thermal shades can be effective in both the summer and winter months for maintaining the atmosphere in the conditioned space.

In a future project with a larger budget I think the TBZ could be implemented without sacrificing the design of the house or impacting the budget too much. It would also be nice to explore low-cost home automation in more detail. If you were able to design the home to automatically control windows, vents, exterior shading and interior shading the cost of mechanical HVAC could be reduced dramatically if not altogether.

As it stands with our current design, we still feel that it will be energy efficient enough to add a reasonably sized PV solar array on the roof to supply most or all of the power to the home. If incentives return to PA in the near future this could be a $5K-$10K decision for the homeowner which is manageable. Then the homeowner can consider things like selling their car in exchange for a nice bike and a solar array that will get their home to zero energy for the rest of their life.

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Keeping Up and Catching Up | 100K House Blog
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1 john umland January 5, 2008 at 9:42 pm

The enertia house is this design taken to the nth degree. see it at
The big concern is that of the fire marshall’s. The excellent airflow is also excellent for smoke and fire. Bummer.
Keep up the good work.
God is good

2 chad January 5, 2008 at 10:38 pm

Thanks! I’ve been searching for this site for a week. I saw it months ago and couldn’t find it again.

3 james D. January 16, 2008 at 10:55 pm

Hey, i just read the article in Metrop! good schtuff. YOu r a pioneer. Congats! I just got a write up in Finland in a little news paper… know anyone who can translate?,3:1005:0:0,4:5:0:1:2008-01-16,104:5:511412,1:0:0:0:0:0 :

4 R Meyer January 28, 2008 at 3:32 am violates principles

Enertia uses bad thermal elements like roof angled glass

See Wikipedia “passive solar building design”
and “sun path”

5 chad January 28, 2008 at 2:33 pm

Meyer – I understand your issue with roof angled glass but if Enertia is achieving zero energy homes and able to allow more daylight in through their window design, does it really matter? Maybe the point is that they could achieve their zero energy goal easier or for less cost with a better design but they seem to have carved out a nice niche for themselves with their current designs.

6 Derek January 31, 2008 at 2:19 pm

The amount of construction material and thermal mass is significant. The swimming pool in the TBZ house also adds to it.

I wonder if the same thing could not be equally achieved as a direct gain configuration with equal mass.

Conversely, if there was no pool and with that amount of solarium glazing, I’d wonder if the area would just overheat?

7 Libitina February 23, 2008 at 1:59 am

I’ve just found this project, and I was wondering why you had not chosen to go with a basement – whether it was purely for financial reasons (and if so, how much a basement changed the costs) or design reasons. This entry points toward design. Was that your primary reason for that choice?

8 chad February 23, 2008 at 3:58 pm

Our primary reason for not including a basement was budget. This would most likely cost us another $20K which we would never be able to afford on our budget. The slab on grade also allows us to very affordably include a radiant heating system for the home which will be very comfortable and efficient.

9 greg June 27, 2008 at 6:01 pm

I have just purchased an Ekose’a home built in 1981 in cincinnati ohio. I have been in it for 2 months, during about 5 or 6 days in that period, the humidity levels were in the 75% range, we have put shades on all the skylites and the upper windows. We have also installed a small room air conditioner with a dehumidifier switch, in the solarium, and this has greatly helped the comfort level. the house is 3100 sq ft and my electric bill runs me so far$135 per month, this is a Lee Porter Butler design. From the 70′s so this is all fairly old design work

10 jjg January 11, 2009 at 1:38 pm

FYI to all,

For several years now we have owned and lived in an “envelope” or “double shell” home that was built in 1981 in the Northeastern part of the USA.

It does not work in this climate and I would not recommend it!!!
Great in theory but absolutely not practical. It has numerous negatives and problems. Several more than listed above.

If we would have known the “issues” with this house I do not think we would have bought it.
My research indicates that there are now many home building technologies that are far better for our type of climate than this old, not clearly thought-out idea.


11 chad January 12, 2009 at 5:14 pm

jjg – Can you give us a bit more detail into the issues you have experienced? It would be very helpful as we have a double envelope design sketched for a future project.


12 Derek January 12, 2009 at 7:38 pm
13 R Meyer January 19, 2009 at 6:57 pm

fyi, ALL of the above Wikipedia articles are extracted from our inexpensive $25 825-page ZED CD-ROM eBook with extensive full-color illustrations, plus over 1600 U.S. Department of Energy presentation slides. It now includes 2 hours of narrated videos and other supplemental materials like Barak Obama’s alternative energy plans. We donated many articles to Wikipedia for the benefit of all, but the specific design and construction details are only available on our comprehensive ZED CD-ROM (hundreds of megabytes long – too large to download online).

DOE recognized us as the foremost 30-year authority on the subject, and featured our all-day “Three Decades Of Lessons Learned” tutorial at their last International Buildings Conference.

Do NOT imitate the many mistakes from the 1981 passive solar design era, which erroneously persist to this day. Do not waste time and money trying to reinvent a square wheel that has already been proven to not work. Do not imitate the obsolete flawed designs from Lee Porter Butler and enertia. Do not use a design that is optimized for one climatic zone in another.

Larry Hartweg is a second-generation energy research scientist with three decades of recognized TBZ experience and a superior track record.

All ZED buildings are VERY location specific, with extensive computer thermal-and-climatic modeling using the free DOE EnergyPLUS software, plus our propietary ZED front-end TBZ data generator.

Our largest TBZ is a new 5-story $250 million Zero Energy Design residential ski lodge for construction at Lake Tahoe CA. It will be earth sheltered on the South side of a mountain facing the North slopes of Sugar Bowl Ski Resort, across the street from the gondola. To the North is Donner Ski Ranch.

14 chad January 20, 2009 at 8:42 am

R Meyer – A bit heavy on plugging your book here, but thanks for the info nonetheless. We may be contacting you guys in the future as we still are interested in the double envelope strategy. For now, we are implementing the Passive House standard to see how that effects our budget compared to the first 100K Homes.

15 Kevin D May 9, 2009 at 10:14 pm

$20K for the basement is REALLY tempting. Although it may only net $20K in resale value, it provides the ability to DOUBLE the living space. This will be worth about $80K to Chad and Courtney when they find out their second child is twins.

Realtors in Denver have this rule of thumb: If the house is in a good neighborhood, no basement, built before 1950, and isn’t brick, then it’s a prime candidate for scraping off.

As sustainable as the 100K is, making sure it lasts 100 years instead of 50 years is the most sustainable quality you can endow it with.

The surplus of vacant lots in Philadelphia makes basements less imperative, though.

16 JER June 16, 2009 at 1:29 pm

I just ordered the ZED CD-rom e-book and will look forward to studying. But I’ve been very interested in the Enertia homes – which seem to combine double shell with increased thermal mass (the “gluelam” beams made of laminated yellow pine). I would be very interested to hear more about the disadvantages. I only have one shot at choosing what to build, so I need to choose wisely. I’ve heard about the fire hazard. What else is a disadvantage, especially for the mid-Atlantic region (PA, DE)?

17 chad June 16, 2009 at 3:36 pm

JER – The Enertia is a great system. I’m sure it’s not cheap, but it is much more proven and clearly explained than what you will find in the ZED documentation.

I would highly recommend using ICF foundation with SIPs walls and roof. You will be 50% better than anything else out there if you start there alone…

18 Derek June 18, 2009 at 7:32 am

This contains another opinion on double envelope houses from a passive solar designer.

19 Ron November 3, 2009 at 6:18 pm

FYI – The zero enegry design CD has virtually NOTHING that’s not on the web site. Very disappointing! It’s a (very poor) glorified sales pitch for their design services. Just a scam IMO.

20 Jill Karlin Butler April 11, 2010 at 6:39 pm

In the 1970s, Lee Porter Butler was ignited to do research on these issues and discover a way that human beings could live comfortably on the earth, without doing any harm. His first ground-breaking work Ekose’a Homes describes his first contribution, “The Gravity geo-thermal envelope”. He continued his research and discoveries until leaving the habiliments of the flesh in 2005. His most recent contribution Ekotecture will free humans from the grid, and promote the earth’s healing through showing humans how to live peaceably together, without the need to kill or plunder for the resources which God gave us to tend. Training us to be good stewards and gardners.

21 Derek April 11, 2010 at 9:44 pm

Energy efficient building is fairly simple. We achieved it with a conventional design. Get sunlight in during winter and stop the heat getting out with good insulation and weathersealing. Add some thermal mass to store the heat. During summer block the sun from getting hitting windows and walls and ventilate like crazy at night. It’s not rocket science.

22 Robert Nemoyer June 18, 2010 at 10:43 am

I am impressed with the envelope designs of the enertia homes, but fell the cost would be too much for me. I asked a builder neighbor who was dismissive ofAlso, my builder neighbor was dismissive of envelope homes because of the cost of double framing. I became interested in high themal mass homes and found a good site at Ranting seems to be common in the passive solar world but I like his idea of building a home out of dry laid concrete block with surface bonding, putting insulation board on the outside of the home and covering that with stucco. While he is death on envelope homes his home could cheaply incorporate that by putting up gypusum wall board on the north side and letting the space between the studs serve as ducts for recyling the air and using a basement. You would be using ballon framing to get the air circulating, but the actual framing is not supporting the roof and you could either paint wood studs with thermoluminesent (sp) paint or use metal studs. It would be expensive but foam insulation between the rafters would allow for the hot air to be stored and circulated. To let the hot air out in the summer one window at the east and west gable could be covered with polyisocyanurate insulation board in the winter and unsealed and opened in the summer. Use a plywood floor in the attic so you can walk to the windows. And possibly put a fan in each window. Since you are building a tight house use earthtubes to bring in precolled air in the summer (50 degrees) and preheated air in the winter (50 degrees). You can always couple this with an airexchanger. I hope to build this home the next time we move. I like the hall less home design at the ZED site which seems a slight improvement on the Islander homes designed by Deb Coleman (google passive solar home plans)

23 Robert Nemoyer June 18, 2010 at 11:09 am

I like the envelope design of Enertia homes, but feel the cost is too high. My builder neighbor rejects envelopes because of the cost of double framing. rejects envelope homes but actually could work well as a cheap envelope home by putting studs against the concrete blocks on the north wall and letting the space between the studs serve as the double wall. This works by building with surface bonded dry laid concrete block, putting insulation board on the outside of the house covered with stucco. The non load bearing studs could either be wood studs with thermoluminesent (sp) paint or metal studs. Putting foam insulation between the rafters would allow for the hot air to be stored and circulated. To let the hot air out in the summer a window at the east and west gables could be covered with polyisocyanurate insulation board in the winter and unsealed and opened in the summer. Use a plywood floor in the attic so you can walk to the windows. And possibly put a fan in each window. Use earthtubes to bring in precolled air in the summer (50 degrees) and preheated air in the winter (50 degrees). You can always couple this with an air exchanger. I like the hall less home design at the ZED site which is similar to the passive solar “Islander” designs of Deb Coleman (google passive solar home plans). Put on a metal roof, paint wood joists, etc, with fire retardent paint, and you have a very solidly built almost fireproof home.

24 John Umland June 18, 2010 at 3:29 pm

Here is a different take, and there are so many.
It uses air tubes through a foot thick pad of concrete and 3 inches of rigid insulation in addition to the sun to keep their houses at a comfortable temperature and humidity year round. They push the air from the peak of the house down into the massive thermal mass in the basement which keeps the house about the same temperature year round.
God is good

25 Brian February 2, 2011 at 1:12 pm

Hi, I have designed and built zero energy homes since the late 70s. I have developed a new building system that allows one to build a net-zero heated home at the same cost as a standard custom house. We have built many alternative design homes: underground, arch, geodesics, sod, living roof, CEB, PAHS, AGS, double wall, straw bale, cob, double shell, shipping container, rammed earth, concrete post and beam, recycled Styrofoam mixed with cement, passive design, etc. I have learned from every project and have continuously refined our craft and abilities. Our new system uses walls that are stressed skin filled with rammed earth and a stressed skin roof. It is designed to last over a hundred years. It optimizes material use, cost, labor efficiency, and sustainability in a self-heating and cooling shell. We use orientation, proper glass, earthen massing, custom air exchangers, earth tubes, convective air drive, led lighting, bioluminescence lighting, plasma lighting, super insulation, home automation and experience. We avoid using things that drive up the cost of a building without a commensurate value gain. Logs, large beams, lots of none recycled foam, and other things are expensive. We avoid such things unless the customer wants them because of their architectural tastes. We believe any luxury a customer wants is fine and that you should not have to limit your quality of life to be green. We have worked with clients that have built for $1 dollar a foot and have others that have spent a 1000 times that just because they felt like it. At the end of the day we strive to deliver the most value possible for the dollar in net-zero heating buildings.


26 Edward Naines May 9, 2011 at 8:47 am

I have own one of these homes in the Milwaukee area since 2005. We love living in the 1983 house and have been restoring it since moving in. One problem we had when first moving in was that the envelope in the attic had collasped. We had it repaired and added a solar vent fan which did help the ventilation of the house. The design does work, my family and I have sat in the 80+ degree solarium on a below freezing Wisconsin day to soak up some rays. I have found ways of improving some of the issues. The biggest difference was painting the solarium all black, this is how we were able to reach 90 degrees in the winter.

27 Aaron June 1, 2012 at 8:03 pm

I am currently looking at a house to buy which is an Ekose’a Des Moines 01 in northern Illinois that was built in 1985. I have read pros and cons and everything inbetween. I am wanting to know if the people who have purchased envelope homes would do it again if they had the choice to do over again. I realize these aren’t the most efficient home available compared to what has been developed. However part of a green home idea is recycling what you have. How can I improve this house, work with the pitfalls and make small changes to make it worth buying.

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