Passive House Delivers 80% Energy Reduction in a 90-year-old House in Santa Cruz

After years of telling friends, "When we remodel our house to Passive House standards we will use 80% less energy than similar homes in the area," and crossing our fingers that the data proved out, we are delighted to share with you our first year's energy data for living in Midori Haus.  

What is Midori Haus?  The name simply means "green house" since Midori is the Japanese word for green and Haus is the German spelling for house.  The house was originally built in 1922, a California Bungalow on the westside of Santa Cruz, California.  Soon after we bought the 89-year-old house in 2010 we discovered Passive House and was convinced that it was the right approach for the remodel.  Graham Irwin of Essential Habitat did both the architectural design and passive house consulting.  Taylor Darling of Santa Cruz Green Builders took on challenging and interesting work and boy did he deliver!  Patrick Splitt of App-Tech designed the solar thermal system and Duane Wilson from Wilson Hydronics installed the system.  The house we bought had good bones and showed signs of deferred maintenance.  So we kept the foundation, most of the framing, floor and roof.  Everything else was replaced.  Deconstruction began in December 2011 and we moved in March 2013.  The house was comfortable.

Our total energy data for the first year of occupancy (March 2013 - February 2014) was only 4,334 kWh.  This includes both electricity and natural gas.  We use solar thermal for hot water but we don't have PV (yet) to offset electricity usage.  When I compared our first year energy usage with the prior occupant's usage I felt validated.  We did indeed use 80% less energy than the prior occupant!

When we did the baseline blower door test on the original house it came in at 22 ACH.  When George Nesbitt of Environmental Design/Build performed the final blower door test it came in at 0.59 ACH.  Taylor and his crew did a meticulous job of air sealing.  Terry Nordbye of Practical House provided advice to the crew on air sealing techniques.

By the way, if you've watched Faith Morgan's Passive House Revolution Film you'll see some mid-construction photos of Midori Haus.

For future reading about Midori Haus I invite you to visit the Midori Haus blog.

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Comment by David Eakin on March 27, 2014 at 8:56pm


I base that on a (somewhat generous) observation of many homes over much observation time. You said that your home originally suffered from "deferred maintenance" (very generous). This also happens to many (but not usually most) used houses on the market. But your home suffered from other factors not related to maintenance (termite/water damage; knob-and-tube wiring; clay sewer pipes, etc.) that had nothing to do with regular home maintenance - these were just instances of materials and techniques commonly used in the 1920s following their natural path of degradation. Nor did your election to re-configure the floor plan to meet your current living space requirements - people use houses differently today than in the past. I see some building materials today having long warranties (50 years typically for "architectural" shingles properly installed, or 100 years for cement-based roofing materials) but most other building materials and appliances used today do not have a guarantee any where near this time length. Add in many (most?) home owners' desire to do cosmetic re-habs of bathrooms every 10-15 years and kitchens every 20-30 years (maybe more frequently - check with some of the planning sources you used for typical projects in your area). Add in environmental changes that few can forecast (just think of the changes you might have made in the design of your home if you knew that water prices would increase by a factor of 100 in the near future), technological changes, and changes in living preferences or for ease of operation (you may get real tired of routinely scraping/painting all your Craftsman woodwork outside, but there may be synthetic materials that will never need maintenance in the future). I see many homes build 50 years ago (and older) that no longer provide good, economical, reasonably-priced shelter with the living preferences of today - unless they are deconstructed and reconstructed as you have done. It would be interesting if Graham could give a lifetime quote for your current design.

Comment by Graham Irwin on March 27, 2014 at 8:31pm

There was confusion about the insulation levels in the attic when it was installed, discovered during the certification process. Fortunately, it was blown-in cellulose, so it was a minor issue to correct.

There are many flat lots with existing buildings that would now require far more robust foundations (read drilled piers and grade beams) when modern engineering criteria are applied. Further, there are all sorts of impact fees and service fee connections that are required with new construction (sometimes with substantial remodels as well, but it varies by jurisdiction.)

Regarding the "accuracy" of your original statement about the merits of remodeling vs demolition, the clients are happy and their home value is secure. A discussion of utility savings is an entirely different matter. Yes, utility savings in more extreme climates are higher, but so are the required envelope measures. I expect these expert homeowners will offer detailed financial analysis in the future.



Comment by David Eakin on March 27, 2014 at 8:03pm


I read through all the blog entries - very informative and entertaining. I also noticed that from start of deconstruction to full-time occupancy took 15 months (with several months' ownership prior during the fact finding/design phases). I found only one section confusing - the addition of 10" of attic cellulose insulation after the original contractor installed 14" as per the PHPP design. No reasoning was provided for this addition outside of the original Passive House design.

However, without any financial information available it is not definitive that your standpoint is any more accurate than mine. That being said, I find it extremely hard to imagine that the extra labor costs in doing an almost complete gut/rehab (with exception to the roof) including framing repairs/modifications and floor deconstruction/refinishing (and the additional alternate living arrangements for the extra de/reconstruction time) - not to mention all the work performed in arduous conditions like the crawlspace - would not add considerably to the costs compared to a new home of equal design/square footage/design goals/material specifications (Craftsman-style homes are still being build today).

I do know that my brother and sister-in-law who live a short distance North of Santa Cruz do not live in a Passive House but pay a trifle to PG&E in natural gas and electric costs compared with my own costs in South East PA. An 80% savings in energy usage would probably translate into not much per month in dollar savings in this locale - so cost savings did not seem to be a motivator in this project.

Kudos to the homeowners who pursued this project, and elected to use some of the most state-of-the-art building science and residential appliance technology while replicating the look/feel of craftsmanship from bygone eras (similar to the "Not So Big House" book series)! My only point is that new construction is usually far less expensive than performing extensive gut/rehab projects of the exact same design and quality due to lower labor costs. But maybe not in the center of a highly desirable location like Santa Cruz where building lot costs are sky high - or unavailable.

Comment by Chie Kawahara on March 27, 2014 at 7:42pm

Good point, David. Everything else was replaced and it was prime time.  We looked at several other homes before buying this one.  Selection criteria included walkability, good solar inventory, yard to grow food, and few other things.  Since we couldn't find unbuilt lot in a walkable area we looked at old homes to scrape and re-build.  There were 2 other homes we bid on (but did not buy) were recently renovated.  It would have felt quite wasteful to undo serviceable elements of the recently renovated house that did not fit into our ultimate design with the Passivhaus performance goals.  So we were quite happy to find this house that was prime for gut-remodel.

With Midori Haus we had a house with good bones with tons of deferred maintenance.  We had knob and tube wiring that needed to be replaced, double-hung windows that did weren't working properly, etc.  So it was the right time for the house to get a makeover.  The original house had nice layout and many would say that the trims and built-in furniture that was worth preserving.  

We did consider the 3 legs of project management triangle:  cost, quality, and time.  Of the 3 legs we were most flexible with time, so when faced with a decision of either "less quality vs. more time" or "more cost vs. more time," we often took the "more time" path.

The decisions homeowners make can be sliced and diced in many different ways.  (Think of the analogies in the book "Zen and the Art of Motorcycle Maintenance") Depending on how you frame those decision you can draw various conclusions.  Perhaps you will build a new passivhaus rather than go down the path we did and that would be the right decision for you.  

One question, David, is the "original design lifetime (30-50 years depending)" you've mentioned.  Where does that come from?  I'm curious....   Thanks for your comment.

Comment by Graham Irwin on March 27, 2014 at 4:56pm


This was a trailblazing project in many ways, and will be much easier to replicate than devise. Beyond that, the cost of new construction would have been higher and and the process harder due to newer, more stringent building code requirements for soils/foundations, etc., and planning regulations, community input, and all the rest of what comes into play when a new structure is proposed in an established neighborhood. Beyond that, there is a general sentiment in society toward preserving the past, and this project was very successful (a lot of great work on the details by the clients and their builder) in that it looks and feels like a methodical restoration of a classic Craftsman home, not a new home built to look old. I am rather persnickety about details, and it looks great to me! I love contemporary architecture as well, but above all, I am a "quintessentialist," and this fits the bill.

The was clients' first remodeling project, and they were methodical in their research and decisions (read their excellent blog to see this and to learn from their hard work: Better yet, contact them and visit! It is a truly beautiful project, and a great triumph for sustainability - they took a 90 year old house, made it better than it was new, and imbued it with the type of performance that gives it another 90 years (at least) of relevance. I have been unable to detect any hint of regret or sadness from these clients, only well-deserved joy and pride.

Kudos, Midori Haus!

PS - Full disclosure: I was the designer of the remodel and Passive House Consultant (energy modeler) honored to be included in this project team.

Comment by David Eakin on March 27, 2014 at 2:26pm

Very interesting! It also points up one of the sad facts of older home improvement - if you "kept the foundation, most of the framing, floor and roof.  Everything else was replaced." and it took you 2 years to complete, what was that total cost compared to building a similar new Passive House (within several months)? I'm guessing far more than the 80% energy cost savings. I am of a mindset right now that unless a building has significant historical significance (and would need to be preserved as such), then it probably should be demolished at the end of its original design lifetime (around 30-50 years depending) and open up the land for new construction. But this flies in the face of a very powerful real estate lobby who's motto is "there is no bad house; it only needs the right buyer".

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