Architects are trained to understand energy conservation through building shape. In theory, a shape that has the least surface area with the greatest volume will be the most efficient. This is because both heating and cooling loads depend on the thermal conductance of the walls and roof.
If you have the least exterior surface area with the greatest interior volume, you will have the most efficient building shape. A sphere would be the most energy efficient design according to this theory. The problem with that is that construction for sphere buildings are costly and impractical.
As discussed in Why You Might Need an Architect: Building Orientation, when you have a long rectangular building in a hot-humid climate, that building could be oriented south to minimize heat gain on the east and west side. Something else that is important for a hot-humid climate is ventilation. How can we address cooling a building on a site located in a hot-humid climate? The answer is with building shape. A long, thin building allows for utilization of prevailing winds.
Architects know that the ideal building shape varies based on the climate and whether or not the building in question is externally loaded or internally loaded. An “externally loaded building” is a building whose energy use is determined by heat loss or gain through the exterior of the building. An “internally loaded building” is a building whose energy use is determined by heat gain from the people who occupy the building, lighting and equipment. For the sake of this discussion, we will focus on externally loaded buildings because houses and small buildings usually fit into this category.
The sketch above communicates that the most ideal shape in a cold climate is a square or cube because it minimizes surface area. Minimizing surface is a key passive design strategy in a cold climate – which is why a two-story building is more efficient than a one-story building.
In temperate climates, the shape has less of an effect. However, an elongated building shape in the east-west direction has advantages with allowing solar heat gain in the winter, passive daylighting, and prevention of summer solar heat gain.
In hot-arid climates, a square shaped building with a courtyard is best since it allows for minimal surface area and maximum natural ventilation. In this building type, these courtyards allow for the introduction of a water element. In hot-arid climates, moisture acts as a coolent in the dry hot summer months.
In hot-humid climates, elongated shapes in the east-west direction are preferred since breezes provide natural cooling. In this climate setting, elongated shapes are used in conjunction with large overhangs.
A design decision like determining the shape of your building matters and it has a big impact on your budget. Climate-specified building shapes do not increase your construction costs significantly. Climate-specified building shapes also save you money in operation costs. Passive Design Strategies are a win for everyone.
One last thing: here in Colorado, we live in an extremely varied region. If I were to go 6 miles west of my house, we would be into the Rocky Mountains with drastic elevation changes. Six miles makes a difference! An architect here in Denver would say we have closer to a temperate climate most years. However, an architect would classify a site 6 miles to the west as a cold climate. This is another reason why you might need an architect: each site has its own idiosyncracies. The architect is responsible and fully trained in these passive design strategies to navigate your site’s particular issues.
Until next time!