AIA DESIGN THEORY – May 2012

Edited by Rebecca Falzano | Photography Trent Bell

Designing for two distinctly different climates

After 20 years of practice in Texas and the Southwestern part of the country, architect Lou Kimball moved to Maine. The last few years have been an interesting transition for him and his work, particularly because of the 180-degree climate shift. “It has challenged the way I had always thought about energy efficiency and design,” he says. “What I’ve come to realize is that the basic architectural concepts are the same, it’s just the implementation that varies with the climate.” MH+D asked him to elaborate.

Q: There are plenty of products and technical solutions out there tailored for climate—some more costly than others. Is there an underlying architectural principle that remains true in both climates?

A: Passive-solar design. In other words, it’s all about the sun. Whether in the hot, arid climate of Texas or the cold climate of Maine, the first concern is solar orientation. The sun tracks across the southern sky in both latitudes, the only difference being the angle of incidence. The south-facing wall of any building is where you can exercise control over when the sun comes in and when you can keep it out. Conveniently enough, the lower sun angles of the North allow for deeper penetration in the winter months, while the higher angles of the South make it easier to keep direct solar gain at bay in the hot summer months. Roughly speaking, in the Southwest we try to keep direct solar gain to a minimum nine months of the year, while still providing for plenty of ventilation. Just the opposite is true here in the north, where solar gain is beneficial nine months of the year.

Q: What does this mean for house shapes in different climates?

A: In the Southwest, a single-story, long, thin house is best, with the long walls facing north and south. The lower sun angles of the east and west are hard to control, so these walls are minimized as much as the site and other constraints will allow. The south-facing wall is opened up with overhangs calculated to keep the direct sun out in the summer months while allowing for deeper penetration in the winter. Clerestory windows are used to the north to let in light without solar gain and to control ventilation on the low-pressure leeward side of the house (the predominate summer breeze is southeast). A single story allows for high ceilings and roof shapes that aid in ventilation.

In the North, the most efficient shape is a square two-story box, which minimizes the ratio of wall surface to usable square footage, making it easier to heat. To maximize solar benefits, that shape is adjusted to a rectangle of the ratio of approximately 1.5 to 1, with the long walls facing north and south. Then, within the limits of reduced R-values for windows as opposed to insulated walls, you maximize the glazing on the south side, again calculating overhang to prevent heat gain in the summer. Add to this a floor material with high thermal mass and you have a good basic passive-solar design. Obviously, fewer windows on the north side, just enough for efficient summer ventilation, is best.

Q: In the southwest, it’s all about dissipating heat. Here, it’s about keeping heat in. How do those strategies differ?

A: In the Southwest, the goal is to design a house that keeps out the heat and has little need for air-conditioning. Again, it’s all about the sun. The best roofs are reflective metal, installed on sleepers to provide an air space just below the metal so that much of the heat is dissipated before reaching the insulation. On one of my projects, we used the same detail for the south- and west-facing walls, providing a ventilated reflective metal skin where we had maximum potential solar gain. Solar gain can also be effectively minimized with high thermal mass, using materials like rammed earth or double-thick stone walls to the south and west to absorb the sun’s heat. A rammed earth house I designed in Austin, with its two-foot-thick walls, achieved an Austin Energy five-star rating (equivalent of LEED Platinum), and the owners rarely use their air-conditioning.

In Maine, it’s all about keeping the heat in. Tight, Passivhaus-style walls and roof assemblies with high R-values are obviously beneficial. Dark roof surfaces that absorb the sun’s energy help in the long winter months. Triple-glazed windows with coatings to maximize heat gain are used here, while in the Southwest simply shading a double-glazed unit will provide more benefit per unit cost than triple glazing. My waterfront clients here in Maine are often faced with a compromise between the best orientation for passive solar and the best orientation for the view, which is often not to the south. It’s important in this situation to look at the house as a whole system, balancing more glass with a less-than-ideal orientation along with fewer windows and additional insulation elsewhere.

Q: Are there any similarities in design for houses of two drastically different climates?

A: For all the differences, what remains the same in designing for both climates is the clients. The primary reason people hire an architect is the belief that the resulting design will improve their lives, that it will somehow be tailored to them in ways an existing house could never be. A good architect helps his or her clients identify what type of house will work best for them and offers creative solutions to achieve their goals. It is the architect’s role to enable people to “be,” to create surroundings in which people see themselves reflected and enriched. Just as no two clients are alike, no two houses should be alike. Each house should be designed to address the client’s particular needs, dreams, and personality. Regardless of the location, a house should feel as if it could be nowhere else—that it fits perfectly with its environment and the people who live there. These things are true regardless of where a house is built.