Passive House
We became interested in the Passive House standard for one simple reason: it is the only approach to design today that produces affordable homes that meet the emissions goals of the Kyoto Protocol. While it is just rolling down the runway here in the US, over 20,000 homes, apartments offices and schools have now been built in Europe, and the standard is being considered as the baseline energy standard for all new structures in the EU in 2015.
What is a Passive House?
Simply put, the Passive House is a house that is certified by the Passive House Institute to meet the following energy standards:
- Use no more than 1.4 kWh/square foot per year in heating energy.
- Use no more than 11 kWh/square foot per year for all energy.
- Allow no more than .6 air changes per hour of air infiltration (at 50 pascals).
What does this mean in laymen’s terms?
A Passive House is super-insulated and nearly airtight. It uses 10% of the heating and cooling energy of homes built to today’s building codes. It is designed as an integrated system, with site, energy, ventilation, air quality, humidity, health, comfort—and economy—all taken into account. In climates like ours, nearly all of the heating energy needed is provided by the household appliances, the body heat of the inhabitants, and sun streaming into the windows. And yes, you can open the windows!
The Passive House is the logical end-product of an approach to sustainable design that focuses upon reductions on the demand side of the energy equation. Rather than adding expensive, high-tech components (solar panels, geothermal heat pumps and the like) to more efficiently meet energy demand, it uses low-tech solutions to eliminate the need for those state-of-the-art products. Our firm is committed to this approach because
- It is more affordable (insulation is cheaper than photovoltaic cells);
- It requires less on-going maintenance through the life of the home (expensive, high-tech things break);
- It is in accord with the way we should approach energy use on the macro level.
What does it look like?
It looks like a normal house. Our first Passive House is designed to show that a PassiveHouse can look like a traditional American home, that style need not be affected by the decision to build a Passive House. Nor does the approach require a particular construction technology. A Passive House can be built using SIPS, double stud walls, TJI walls, or any other wall system that can be made to achieve the required insulation values. A few things will give it away as a Passive House, however:
- The exterior walls will be thicker—in our area, by about 6 to 8 inches.
- Windows will be triple-glazed, with a lot of them facing south and fewer facing north, east and west.
- South facing windows will be protected from summer sun by overhangs, awnings or canopies.
- It will be extremely quiet.
- It will be extremely comfortable, with no air stratification or drafts.
- You won’t find a furnace in it.
But won’t it be unhealthy to have a house sealed that tight?
To the contrary. The house is designed with products that do not outgas formaldehyde or volatile organic compounds. More importantly, it has a simple but quite sophisticated ventilation system that monitors and manages the amount of fresh air that comes into the house. Here’s how it works:
- A small cube about 30” per side—the energy recovery ventilator (ERV)— exchanges stale interior air for fresh exterior air and swaps the heat and humidity between the two streams as the pass by each other.
- Ducts small enough to fit in a stud cavity distribute a small continuous stream of fresh air to the living spaces. Registers in room ceilings are the size of a recessed light fixture.
- Other small ducts collect air in the kitchen and bathrooms and take it out of the house. This means that unlike in a traditional house, where the same air gets recirculated around and around the air handling system, the air in a passive House effectively makes a one-way trip through the house.
- A small heat exchanger in the supply air ductwork, connected to the hot water heater, adds the small amount of wintertime heat required.
- Similarly, a ducted variable refrigerant flow mini-split heat pump provides all the cooling and dehumidification necessary in summertime.
Won’t it be more expensive?
The house we are building now in Bethesda will be about 8% more expensive in terms of bricks and mortar cost. That ends up being about 4-5% more in terms of total project costs. Projected monthly energy savings ($520), when compared to a conventional home, essentially offset the increased monthly mortgage cost. And those monthly energy savings are only going to go up.
A multi-unit Passive house Housing project now being built in Yellow Springs, Ohio was also priced both ways, and in that case, the Passive House construction came in at only 4.8% higher than standard construction.
Want to learn more?
Visit the blog for our Passive House now going up in Bethesda.
