Wed, Dec 1, 2010
By Léa Khayata
When Justin Stewart bought a brownstone to renovate in Park Slope last year, he wanted to see how close to zero energy consumption he could get. “The question was, how do we get there?” he says. Then he heard about the German “passive house” standard that promised energy reductions up to 90 percent.
He knew he had found the perfect match for him.
The passive house standard is a series of building requirements aimed at creating a virtually airtight envelope to insulate the house from outside temperature changes.
Most heat is provided by passive solar gain, human presence and ordinary electrical devices.
Unlike other tightly build houses, there is no mold and indoor air quality problem. The house is allowed to “breathe” thanks to a ventilation and heat exchange system. The air is therefore much cleaner than in traditional houses, and the temperature is the same throughout the house. In a traditional building, it tends to vary widely from one floor to the other because of air leaks, creating discomfort for the inhabitants. In a passive house, the energy bill is reduced by about 90 percent.
Around 15,000 passive houses have been built or renovated in Europe, mostly in Germany and Austria. Only 13 houses using the standard have been built in the United States so far. The first passive house in the New York area was recently completed in Park Slope, just a few blocks from Stewart’s. Two more houses are in renovation in the neighborhood and a dozen are in the design phase in the city.
When Stewart decided to go passive with his Park Slope brownstone, he hired Jordan Goldman, a passive house consultant, to help the architect design the renovation. All the work concentrates on the exterior walls, the windows and the ventilation system.
The first step is to strip the existing walls from the inside and add cellulose fiber to increase the insulation. The traditional windows are replaced by triple-glazed ones to reduce any air-leakage to a minimum. The last step will be the installation of the ventilation system throughout the building to insure air quality.
Jeremy Shannon, a passive house consultant and architect, says he’s having no trouble selling the concept to his clients. “The slower economy is helping the idea of passive houses. American architects have been more focused on design in the last years, but this is rapidly changing,” says Shannon. Passive houses don’t focus on the outside look. “What I like about passive houses is that from the outside, they look like any other house.” Shannon says.
The Passive House Institute US, which is associated with the Passive House Institute in Germany, is in charge of monitoring the standards in the United States. So far the institute has certified 14 architects in New York City, seven of whom are in Brooklyn. The projects underway in the borough are mostly residential renovations, making them very different from the other projects completed in the U.S., which are mostly stand alone constructions.
To be effective, a passive house renovation has to be designed and carefully planned from the beginning, said Goldman, who is consultant for the Stewart’s house. “We got really interested in passive houses because it sets a formula, a system that you have to follow, which makes it less hypothetical,” says Stewart. Because the cornerstone of a passive house is the walls and the ventilation system, changes or additions aren’t possible in the middle of the project. The whole building should be considered as a system. “If the design is done from early on, it can be very inexpensive,” says Shannon.
“The walls of a house are something you don’t do again. Our brownstone was built 120 years ago and it has been the same walls since the beginning,” says Stewart, who didn’t hesitate to spend the extra money required for the project, estimated between 3 percent and 5 percent of the total cost. “Putting less in the kitchen, that’s fine to me, we’ll work on it in a few years,” he says.
Walls are almost three times thicker than in a traditional house (around 18 inches), which is space taken from the inside of the house. But the Stewarts didn’t consider this a problem. “It’s excessive for a single family to live in so much space, so we feel obliged to consume less,” says Stewart.
Passive houses are more expensive to build in the U.S., in part because of the lack of available materials and products. For the brownstone that Shannon just finished renovating in a landmarked area in Park Slope, they had to import the windows and have them custom-made to fit the landmark requirements, which consequently rose the costs. The next house Shannon is renovating is situated just one block outside of the landmarked area, cutting window costs in half. “I hope that this house cost as much as a normal house,” Shannon says.
“We’re expecting a very low energy bill, it definitely excites me,” says Stewart.
Once the house is completed, the owners can chose to have it certified by the Passive house Institute US, which runs a series of tests to make sure it complies with the requirements. The last one is the most difficult to pass.