There are a lot of green building techniques to make a house more energy and resource efficient than a conventional building — one of these, Passive House, has been showing up in the news more recently as a leading green standard and certification of an energy efficient building. But even for us it can be hard to keep track of the various terms and certifications, so we've asked a green architect, Mark Miller, to help explain Passive House building:
Mark Miller is a registered architect and is in the process of becoming a Certified Passive House Consultant. He is the principal of architecture firm, Mark A. Miller Architects + Builders, and owner of Passive House consulting company, Passive House Midwest.
What makes a Passive House different than a conventional house?
A Passive House is extremely conscious about keeping it's conditioned air "in" and the unwanted unconditioned air "out". This means extra special care is taken in the quality of the details making up the building's shell:
- Super insulated walls
- High performing triple glazed windows, with many seals and locks
- No pipe penetrations in the exterior wall
- No kitchen or bath exhaust fan roof caps letting cold air into the house
- An air tight layer stopping wind driven moist air from getting into the shell
- Use of an Energy Recovery Ventilator or Heat Recovery Ventilator operating 24/7 continuously exhuasting stale air, and bringing in fresh outside air, while "recovering" 85% of the heat energy that would be exhausted, and returning that energy to the incoming air
- No conventional furnace
- Up to 90% reduction in a conventional homes energy bills
As a self-described green architect, how do certified Passive Houses compare to your other homes in terms of energy efficiency and sustainable design aspects? How is the design and construction process different?
Passive Houses at the moment seem to be the best energy efficient design strategy using conventional building components; it outperforms just about everything. The simple theory is: reduce the heating and cooling needs of the home, thus one hardly needs to produce any heating or cooling to meet this minuscule demand. This concept can be applied to many aspects of life: finances; shopping, vehicle fuel economy, etc. — it's a universal theme.
The construction process is similar to my other green projects, but greater attention is given to how the same building materials are assembled: no gaps in the insulation; no pipes in the exterior walls; no thermal bridges (a building component that assists heat energy getting from the exterior to the interior or vice-versa); insulation levels are typically double code requirements, depending on exact climate; attention to window types, sizes and locations on the envelope; etc. Additionally, before insulation gets installed, it is recommended to do a blower door test, to understand how air-tight the shell is. This provides the opportunity to walk around the house and seal up any areas where you can hear and feel air rushing in. Then with insulation and drywall, the air-tightness gets even better — this is not done with conventional home building. Because of the attention to detail, a Passive House is typically higher in quality.
Certified Passive House structures have been appearing in the news a lot lately, but people have building passively for years. What's the difference, if any?
When folks hear the phrase "Passive House" most think this is a "Passive Solar House", but these are two different techniques. A passive solar home is attempting to maximize the solar heat gain available passively through mainly abundant south-facing glazing. They then attempt to store this heat made during the day, into building components such as concrete floors, water tanks or trombe walls, for use at night. On the other hand, a "Passive House" is much less concerned about maximizing the passive solar heat gained during the day, and how to store it, but is more concerned with keeping whatever heat is in the house, in the house. The focus is more on the quality of the thermal envelope and this is why many Passive Homes can be comfortably heated with just a 1000w hair dryer!
There are a lot of green certifications out there: LEED, Energy Star, Green Globes, etc. What makes Passive House different? Why should a homeowner choose this certification over others?
LEED, for example, is more focused on how many "green goodies" can be incorporated into a building project — the more items used on the list, the more points you "win". Energy Star and others focus on the overall performance of the components that make up a building. Passive House is in this category, as it is looking at the whole of the building and it's systems. Twenty years of studying the earliest passive houses, has gone back into the computer software that analyzes how these buildings perform, so the projected results are extremely accurate. When you design a passive house, you know exactly what you will get, based on your design decisions "before you build it". You know how much energy your home will use and that's powerful knowledge — this is just a great tool to have. Passive Houses are the result of studying the cost versus performance of building systems, and this seems to be the best bang for the buck. You won't see $150,000 spent on a PV system in a Passive House to claim you get $5-a-month back from the power company, it just doesn't make good sense.
Is there any system in place to track the building's performance, after construction, to ensure the projected energy use matches up with the actual energy use?
The PH consultant helps with this, monitoring fuel usage, and balancing the homes ventilation system. There are also more and more "smart" home technologies that give home owners the ability to monitor their energy use and performance.
What does Passive House certification cost? Are Passive Houses more expensive to build than non-certified homes?
Passive Houses are slightly more expensive to build than conventional homes. In Germany, where most building materials are already improved to meet Passive House standards, there is about a 5% increase in overall costs of construction. In the US where windows, for example, aren't even close to matching up with the performance of standard German windows, it's not as easy to get high performing products. This is, and will be, changing as Passive House spreads through the US. Certified Passive Houses in the US aim for being no more than 10-15% more expensive than a conventional house. There are savings in having a much simpler HVAC system, for example you don't need expensive geothermal or radiant heat. On the other hand, super efficient windows will cost more than even the best Marvin windows. Most builders buy PH certified windows from Germany, such as Optiwin. Otherwise, the only company in the US to make high enough performing windows is Serious Materials. Other PH certified building materials are also in the works for the US marketplace.
Are there any subsidies or tax benefits to having a certified house?
Yes, in some states, and this is continuously increasing as the movement continues to grow. Keep checking as Passive House consultants are working with municipalities to get PH added to their lists of approved for subsidies and tax benefits.
What does it take to become a Passive House Consultant?
A few times a year the Passive House Institute US (PHIUS) holds a nine day training program. One must take this, then pass a very difficult final exam. You're not done yet, now you have to actually do one project and have it meet certification to the PH standard — after this, one becomes a "Certified Passive House Consultant". The beautiful thing about this movement is, like the beginning of computers, there was this wonderful exchange amongst the early computer inventors, everyone sharing information, to help all push the limits of what this new tool can do. Likewise, there are Passive House Alliances in key areas in the US. PH consultants are sharing the latest building science information and discoveries with each other, so we all can make the highest performing buildings available. The goal is to help our planet earth, by reducing one of the largest users of fossil fuels, the building industry.
For more information:
Mark A. Miller is a practicing Architect/Builder/Developer living in Chicago who designs projects around the country. His studio has a reputation for designing and building high performing energy efficient homes that speak to the soul. Mark has recently co-founded the Passive House Alliance Chicago and is lecturing about The Passive House Standard throughout the Midwest United States. You can learn more about his unique approach to designing thoughtful homes at his websites: Zen + Architecture and Passive House Midwest.
- California's First Certified Passive House
- Passive Home Design
- Habitat for Humanity Plans Passive House in Vermont
- Green Boston Rebuild Aims for Passive House Efficiency
(Image: Passive House Institute. Originally published 2010-10-13)