In the world of sustainable construction, there are dozens of certification programs available to choose from. While this is good news for the increase of responsibly designed and healthy buildings, it can be overwhelming to those who are not in the industry. If you are about to build a new home, how do you decide which program to follow? While LEED is arguably the most popular program available, and offers many excellent benefits and guidelines, it may not be right for your particular project. Or perhaps a combination of programs is appropriate, as we are doing for Meadowlark House. If you are serious about building sustainably, we would encourage you to research all the programs out there and weigh the pros and cons of each in relation to your specific project.
For our next eco-home, we decided early on that we wanted to demonstrate a building standard that has been around for over two decades but remains relatively unknown in the United States. That standard, called Passive House, was developed in Germany by two professors starting in the late 1980s. It was brought to the U.S. in 2006 by the Passive House Institute U.S. The standard is a design process, not a supplemental program to a building - meaning its components have to be taken into account from the beginning of a project. The design of a Passive House centers around six principles used together to create an extremely energy efficient home: passive solar design, superinsulation, high performance windows, airtightness, ventilation, and space heating. Through the use of Passive House, energy needs are reduced up to 90% compared to traditional, conventionally built homes.
Overall, the certification process is performance based, and this is probably the biggest difference compared to other programs currently out there. The materials used to achieve the required energy targets are up to the design team. This is one of the reasons we like the standard, because of the ultra-low energy savings. (Note: We are using the LEED for Homes rating system to guide other elements of the design, the material selection, and construction process, which will be detailed more in this blog over the coming months).
As of 2010, there are approximately 25,000 buildings constructed using the Passive House standard, most of them in German-speaking countries and Scandinavia. There are only 13 certified homes in the United States with a few dozen more currently under construction. We hope that Meadowlark will help educate the public and spread the word about this fantastic building standard.
To learn more about the six design principles found in the Passive House standard, click through using the link below.
Passive solar design is a concept that has been around for a long time. The basic idea as it is applied to Passive House is to create a compact building shape with the majority of windows oriented to the south to take advantage of natural daylighting and heat from the sun (which is called passive solar gain). A system for shading the windows is needed to keep summer sun out while also allowing for the winter sun to come in. Shading can be done a number of ways but is usually accomplished through deep overhangs or trees. A thermal mass is needed to store energy, both for heating and cooling. In the case of Meadowlark House, we are using a concrete floor.
Traditional homes in America are built using 2x4 wood studs which are then filled with insulation, giving the wall an average R-value of R-10. (R-value is a term that refers to the heat resistance that makes up a wall system, i.e., studs, insulation, drywall, exterior siding. The higher the R-value, the less heat is lost through the wall and the more money you save on energy). While this is a less expensive way to construct a home, it doesn't provide much in the way of preventing heat loss through the walls. Homes built using Passive House are superinsulated, meaning the walls are very thick to allow for high levels of insulation. In Meadowlark House, our total wall thickness will be over 14 inches and it will have an overall R-value of almost R-40. The superinsulation of passive houses isn't limited to the walls only. The R-value of our roof will be R-60 and the foundation and floor slab will be R-50.
High Performance Windows
Average windows today are typically double pane and low-e (low-emittance, typically a microscopically thin metal coating that reduces heat loss through the window). Windows used in Passive Houses are triple pane, with especially high R-values (or in the case of windows, low U-values). South facing windows are designed to let in more heat from the sun than windows on the west, east and north sides of the building.
Passive Houses are considerably more airtight than conventionally constructed homes. A large amount of money is lost due to warm or cool air passing through a house, requiring the homeowner to run the heating or cooling system more often. To prevent air loss, every construction joint and service penetration must be carefully sealed. A mechanical ventilation system is then used to control the amount of air coming into and leaving the home.
When exterior temperatures allow for it, the best way to ventilate a house, any house, is by opening windows. Depending on the climate, this can only be done during for a relatively small percentage of the year. The rest of the time, Passive Houses use what is called an energy recovery ventilator (ERV) to carefully control the amount of air passing through. ERVs also recover the heat of exiting air and transfer it to the air entering the home, further reducing the need to use your heating and cooling system.
In addition to the use of passive solar gain mentioned above to provide heat, Passive Houses take advantage of heat sources already found inside the home. These include appliances, electric lighting sources and the heat that is naturally released from human bodies. All of this, together with the conservation measures described above, eliminates the need for a conventional heating and cooling system. Because the climate in Kansas hits both extremes of hot and cold, we will be installing supplemental heating and cooling through a mini split heat pump and baseboard electric heaters. These will only be needed on the hottest and coldest days of the year.
Learn More About Existing Passive House Projects:
The Smith House (the first Passive House in the U.S.) - Champaign, IL
Hudson Passive Project - Claverack, NY
Prescott Passive House - Kansas City, Kansas
The Passive House website also has a great list of existing projects.