We recently cornered Moskovitz and pressured her to answer all our questions. What better expert on passive houses is there than someone who builds them and has studied them extensively? Her book The Greenest Home, which is available at your finest online retailers and hopefully your local book store, is chock full of beautiful images along with lots of great technical info that should answer any of your more serious questions about the nature of passive house construction.
Inhabitat: Why do you think passive houses are the best standard for green building out there?
Julie Torres Moskovitz: A certified Passive House project performs close to its modeled energy use and it is proven to work. It is a performance-based system that prioritizes conserving energy. The project is air tight and insulated with minimized thermal bridges and bolstered with technological aspects such as high performance windows and doors coupled with intelligent membranes, tapes, and an HRV (heating recovery ventilation) unit. I like that if you follow the PHPP (Passive House Planning Package) and the building meets the standards then you know that you have built yourself an extremely energy-efficient and well-performing building. This is exciting as there is lots of concern about climate change and reducing carbon footprint but there is little in the way of a tried-and-true path to make that energy reduction happen. Passive House is it, and your air quality and well-being are improved while reducing your energy consumption so you are not required to sacrifice your quality of life. It’s not the only answer but it’s a big piece of the puzzle for the building sector.
Inhabitat: Can you explain the difference between the European standards and American?
Julie Torres Moskovitz: The Passive House Institute is based in Darmstadt, Germany and they created the PHPP (Passive House Planning Package) software and they certify designers, tradesmen, and even products such as windows and HRVs (heat recovery ventilators). The Passive House standards are set by PHI but there are different entities in different regions in the world that certify projects. In my book, The Greenest Home, I cover eighteen recent case studies and clearly point out which projects are certified or not and by which entity. Most projects I feature are certified by PHI even the American projects but some were certified by PHIUS, Minergie, and the Flemish Passive House Platform.
It’s important to note that all of these certifying agencies, whether PHI, PHIUS, or other regional entities, are working towards the broader goal of helping create a pathway to high performance buildings.
Inhabitat: How are different climate zones accounted for in the Passive House standards?
Julie Torres Moskovitz: First, it’s important to note that Passive House addresses any climate on the planet because accurate weather data and specific site location information is inputted into the PPHP (Passive House Planning Package) software modeling and that affects how the design of that building is addressed. And certainly colder climates require more thermal insulation to make the minimum performance requirements.
That said, energy equity is important and so regardless of a building’s location it must meet minimum heating/cooling demand and primary energy demand requirements to qualify as a Passive House.
Inhabitat: What are some of the important new technologies and systems that make it possible to achieve the current efficiencies of passive houses?
Julie Torres Moskovitz: As I mention in the Introduction of The Greenest Home, the energy-modeling software and high-performance products now on the market have ushered in new levels of possible efficiency.
The most important tool that is available to designers is the PHPP (Passive House Planning Package) developed by the Passive House Institute that allows designers to enter detailed information about their projects and to receive in return an instant analysis of how each component is working together and responding to the site conditions to create a low-energy house.
The high performance windows and doors specified for Passive House buildings virtually eliminate thermal bridging at their frames and are triple glazed. It is also very helpful that products are Passive House certified, so that you can count on them to achieve Passive House standards. The films on the glazing enable solar gains that provide heat to the building. Intelligent membranes and tapes enable builders to overlap all of the exterior walls, roof, and slab so that each element including around windows and doors is sealed and airtight. Also central to the Passive House concept is the reliance on an HRV (heat recovery ventilation) system that provides constant fresh air to the home and it does so efficiently transferring heat from exhaust air to incoming fresh air in colder months.
Inhabitat: Do you have any knowledge about costs of passive houses compared to say a LEED house or standard home construction costs? How easy is it to do for a retrofit project?
Julie Torres Moskovitz: The Passive House community has been finding a 5 to 10% increase compared to standard construction costs. Some architects say that they can build a Passive House for the same cost as standard construction although, the two architects who told me this have been working specifically on multifamily Passive House projects.
With our Tighthouse project we determined from synthesizing 12 months of data collected from monitoring the house that the 5% premium the clients paid towards Passive House design will be paid off in 9 years. The utility bills are very low in the house and the first annual energy savings equals $2898.00 compared to a standard construction project of the same square footage (we compared the Tighthouse to RECS data for a similar square footage home in New York State. Here is a link http://www.eia.gov/consumption/residential/).
Inhabitat: While writing this book, what surprised you most about sustainable architecture, green building or passive houses?
Julie Torres Moskovitz: Well, I had been working on sustainably designed projects for years but not until I took the Passive House training courses did I realize how special and comprehensive Passive House Design is. First of all, I always believe in collaboration and I was wowed by the collaboration of scientists, designers, and builders in Passive House. Physicists are behind the Passive House energy-modeling software and it makes sense to me that in order to achieve a building that is optimized and low-energy that it would require scientists and architects to sit down together. The NASA space program, for example, requires the science mind but also a designer who can envision the possibilities.
Inhabitat: What is your personal experience with passive house construction?
Julie Torres Moskovitz: I wrote The Greenest Home Superinsulated and Passive House Design while completing construction on a Passive House retrofit project in Brooklyn, called Tighthouse. It is the first certified Passive House project in NYC.
While researching and designing the Tighthouse we became very interested in discovering what other Passive House projects were out there either completed or in the works. There was some information on projects via the internet but the stories were light and didn’t explain details or challenging aspects that the homeowner or builder came up against. I was surprised that I couldn’t find a book that explained it all and knew that I had to write this book, which is the book I was looking for and needed.
Working on a Passive House project while writing the book helped to contextualize the research and made me extra curious as I was interviewing the architects, engineers, and owners involved in the 18 case studies highlighted in The Greenest Home. I am someone who has to learn through doing and it was important that I experience a Passive House project from start to finish. The project was really a learning laboratory for us. During construction I learned to gauge air tightness from strategic blower door tests and during those blower door tests we would see how certain materials were performing. Now we are monitoring the home and able to make tweaks to improve the performance and take away important information to inform future projects.
I hope that I can build a practice that is all Passive House and low energy projects as its hard to go back to standard construction practices after you have figured out Passive House detailing.
Images Courtesy of Julie Torres Moskovitz for The Greenest Home published by Princeton Architectural Press