Old homes can be full of charm, but no one will mistake them for being energy efficient. Especially when the heating and cooling bills arrive.
"You've got these beautiful old homes, and they really perform horribly," says Michael Ingui, a partner at Baxt Ingui Architects.
They leak air, release heat and allow pollutants and allergens in. Many have bulky, noisy radiators that take up a lot of floor space.
Plus, since many old homes have poorly insulated exterior walls, the radiator is putting 40% of its energy into heating the floor and exterior wall before it even heats the interior of the house, Ingui said.
But what if you could boost the energy efficiency of a historic home, drastically reduce the cost of heating and cooling, and improve the indoor air quality?
That's where passive design comes in. These design principles emphasize an airtight space inside the home, with continuous insulation and fresh air filters for indoor air quality. Done properly, the techniques can significantly reduce or possibly eliminate the need for a heating system, greatly reducing energy consumption.
Ingui, who is currently working on nine passive home renovations in Brooklyn and Manhattan, says that by naturally heating the home and eliminating heating bills, the return on investment typically happens between two and five years.
What is 'passive house'?
In a passive house, the interior of a home is insulated, the wall seams and window frames are sealed, triple pane windows are installed and, in some buildings, a thick plastic shield is placed under the foundation. These simple techniques seal the home up like a box by creating a protected barrier that prevents conditioned air from leaking out and irritants like dust, pollen, bugs and mice from getting in.
A passive home also has one or more units that provide air conditioning and can also provide heat, which is sparingly needed, and a separate air filter that brings fresh air into the home.
The fireplace, a notoriously open and leaky system, can also be retrofitted to be outside of the sealed space of the home, with glass doors on the front.
The passive house technique was developed more than 25 years ago in Germany. But the design measures had to be modified to suit varying climates in other parts of the world. In the past few years, the number of projects in the US has grown significantly.
"The standard worked perfectly fine in a central European climate, but not so much in Louisiana or Minneapolis," says Mike Knezovich, director of communications at the Passive House Institute US, one of the certification organizations.
The number of apartments or homes that PHIUS alone has certified, or is in the process of certifying, nearly tripled between 2017 and 2018, from 323 to 1,161, with even more projected in 2019.
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"Our mission is to get more of these buildings built and retrofitted," says Knezovich. "We're all about reducing the carbon footprint of buildings, but we can't make it complicated or expensive. It has really taken off because it makes building and retrofitting more cost-effective and practical."
While other green building standards, like Leadership in Energy and Environmental Design (LEED), take into account many dimensions of a building like site selection, water efficiency and materials used, the passive house certification is more specific, focusing on energy use and building performance. But the two standards are not mutually exclusive -- a home could be a LEED-certified passive house.
New York City's Landmarks Preservation Commission said in a statement to CNN that owners of historic buildings "can, and should, take measures to improve energy efficiency." The commission streamlined its approval process for certain aspects of passive house projects and it staffs a desk focused on energy retrofit projects.
"You gain a better house," Ingui says. "You gain a healthier house. You gain money in your pocket for not paying for heating. It's a pretty wild approach to think that you could actually save the environment while having a better home."
But what do you have to give up?
Homeowners are often skeptical about the benefits of passive design, says Ingui, who has developed a clearing house of information called the Passive House Accelerator for designers. tradespeople and homeowners.
"I find that when you start the conversation by saying that you're going to be able to save 80% of your heating and cooling bills, they don't get excited about it. They wonder: 'What am I losing?' "
There are some challenges to be aware of in a passive design project.
While strategies can be used piecemeal -- buying triple pane windows that open and close just like typical windows when you replace them, for example -- the most powerful effects will be seen with a complete renovation. That makes it a pretty substantial -- and more expensive -- project. A passive house renovation can add about 2% to 4% to a home's overall renovation costs, according to Ingui.
"You're spending some more money on sealed walls," he says. "You're spending some more money on the insulation and much better windows."
And be warned: even without heat it may get a little too warm in the winter.
"The biggest thing people have to get used to is that they hardly have to heat their house," says Ingui.
After his own home was retrofitted as a passive house 2017, Ingui hosted a New Year's Eve party.
"It was 10 degrees outside and it was so hot in the house we were opening the back door and I had not yet turned my heat on once that winter." he said. "I turned to everyone and said: 'This is passive house!'"