Scott Bernhard, AIA, directs the Tulane City Center, which houses the applied-research and outreach programs of the Tulane University School of Architecture. He recently launched the nonprofit Lime Agency for Sustainable Hot/Humid Design with his wife, Carrie Bernhard.
Credit: Rick Oliver
New Orleans is famous for its heat and humidity, of course. But it’s far from singular climate-wise, says the husband-and-wife team of Scott Bernhard, AIA, and Carrie Bernhard.
The Bernhards—Carrie, 40, who trained as an architect, and Scott, 47, who teaches at the Tulane University School of Architecture and directs the Tulane City Center—estimate that some 3.3 billion people live between the latitudes of 40 degrees North and 40 degrees South. (The region between the Tropic of Cancer, which is located about 23 degrees north of the equator, and the Tropic of Capricorn, about 23 degrees south of the equator, is the tropical zone; the areas adjacent to them are considered subtropical, according to the Trewartha climate-classification system.) Faced with robust population growth in these regions, architects working there will be increasingly called upon to design sustainable buildings.
When the Bernhards helped oversee a design competition for New Orleans following Hurricane Katrina, they soon realized that many of those who submitted designs had ideas that were wildly impractical for heat and humidity. So they set about creating a nonprofit to spread the word. They named it after a fruit often associated with the tropics, and one that suggests the color of fecundity. The Lime Agency for Sustainable Hot/Humid Design is not affiliated with Tulane or any other institution, and is registered as a nonprofit, but is not yet a 501(c)(3) organization.
“I feel like this is an entity that should already have existed,” Scott says. ”A whole lot of people are looking for this information.” The Bernhards are currently preparing a series of downloadable guides about the fundamentals of designing for heat and humidity. Architect sat down to talk with Scott Bernhard recently about building in these challenging environments.
Why did you decide to start the Lime Agency? Was there a specific moment when you realized that architects just didn’t get it?
My wife was in charge of [a] single-family home competition [after Katrina], and she and I prepared a booklet about traditional New Orleans house types so competitors could have a sense of what New Orleans buildings were about. We stressed how 19th-century buildings kept people cool.
Of course, nobody paid any attention to that. And Carrie was aghast at what was submitted—some of which were very elegant design proposals, but very few of which were good ideas in terms of this climate.
Where do you start in designing for heat and humidity?
Well, it comes down to this whole notion of insulation and operable windows. In the engineer’s mind, the ideal structure is entirely sealed, and there’s some kind of air lock to enter and exit. This air exchange is predicated on mechanical devices, and you bring in the minimum amount of exterior air, which has to be conditioned.
My wife and I, on the other hand, live in an 1840s building. All the devices that existed in the 19th and early 20th century to cool things are in play—we have tons of windows and they’re on different sides, and we can open them in different proportions to create Venturi effects. But the bottom line is, we have a leaky building. So our house is inefficient at mechanical cooling and extremely efficient at passive cooling.
Technology seems to favor the sealed building. And the more we get into this, the more we really realize that, while we think of hot, humid climate resilience as being predicated first on passive means and the logic of building form, the rest of the world thinks of it as a technical issue.
What are some of the elements that architects should pay attention to when designing for the tropics?
Building orientation may be the most obvious. Then, thinking about how the breeze moves, how openings can be configured, how what we call the penumbra of shading works around the building. There’s a kind of a core, and if you can keep the core in shade all the time, then you’ll never have that sort of driving radiant and convective heat gain. And that penumbra is the attic, and the galleries, balconies, or outdoor spaces.
I lived in the French Quarter for many years. It’s close to the river; breezes move through, buildings are masonry, [and] they’re almost all surrounded by that penumbra of shading devices. If you live in a party-wall building in the Quarter—which most of them are—50 to 70 percent of your perimeter is entirely sealed by your neighbors, and those two narrow ends are almost entirely operable to pull breezes through.
Density of the kind we have in the French Quarter produces a kind of cooling effect itself, whereas little houses staked out in the middle of a lot without enough trees around them, I mean, it’s miserable.
There’s sun and heat, and then there’s the humidity here.
Getting water out of the air is very difficult, and water is going to hold the heat indefinitely. That’s why it’s hot at night here when it’s cool at night in California.
The biggest thing we have going for us is to keep the air moving. If we’re raising buildings up off the ground for whatever reasons, we definitely want to take advantage of the fact that there’s more breeze up there. If we’re configuring window openings in the building, we should configure them so that they should be available for breeze.
There should be a ceiling fan in every space, configured just the right way to keep people cool.
What are some of the other issues?
Big walls of glass facing east, west, and south are a problem. Facing the glass south is so much easier to manipulate, and yet when people do face the glass south, they don’t manipulate it—they don’t put in the overhangs and they don’t calculate the sunscreen for it. These are just such simple things, I think.
And of course, if you’re trying to cool something passively, a long thin shape makes a lot of sense. If you’re trying to cool something mechanically, a sphere or a cube is the ideal figure. They’re almost antithetical to one another.
My sense is we have a very short heating season [in New Orleans], and we have months where you can operate passively with little attention paid to it, so I would err on the side of passive cooling.
Yet, we’re trying not to make the Lime Agency predicated on my opinion on how these things should go. We’re trying to present data, design possibilities, and then the decision is up to the people configuring the building.
Are you finding much research elsewhere on how to work in this sort of environment?
That’s an odd thing—we spend a lot of time looking for other people doing this research and people who want to collaborate.
If you think about it, though, the financial motivation to develop passive systems is quite low. If it’s just a matter of configuring the building, and changing lifestyle a little bit, nobody’s making any money off that.