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Mid-doors: The zone between inside and outside that could change building design

Mid-door spaces offer protection from the elements but allow in more sunlight and allow more temperature fluctuation than an indoor space. And they can offer a calming, nature-filled break from dull offices.

Mid-doors: The zone between inside and outside that could change building design
The Ford Foundation Building’s atrium. [Photo: Dario Cantatore/Getty Images]
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What makes the indoors, indoors? It isn’t the presence of a “door” that you are “in,” unless you consider deep underground subway stations (without doors) as outdoors. But is a cave indoors? Even deep underground, fully protected from the elements, the wildness of a cave makes one hesitant to consider it truly “indoors.”

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Perhaps, then, the definition of indoors and outdoors is not so definite. Some elements seem essential to the indoors: protection from the elements, especially rain, wind, sun. Beyond that, things become fuzzy. Most subway stations aren’t heated or cooled yet give the impression of indoors. We encounter many situations that exhibit some element of protection from the elements, yet aren’t fully heated or cooled, or don’t have full protection from rain, wind, and sun: amphitheaters, bus shelters, event tents, ballparks, and even greenhouses.

Rather than thinking of indoors and outdoors as a binary condition, we need to acknowledge there is a spectrum from indoors to outdoors. The concept of a spectrum is already familiar for other words we use to describe the environment around us. Although we think of “light” and “dark” as opposites, it’s easy to see that they actually represent different ends of a spectrum. When passing through a series of spaces with increasingly brighter light, at what point is the space suddenly considered “light”? The same principle applies to noisy and quiet: clear ends of a spectrum, but there is a lot of middle ground. The middle ground of indoors is so unfamiliar that English lacks vocabulary for describing it. A room might be lighter or louder, but is it more indoors or more outdoors?

Milan Central Station. [Photo: scaliger/iStock]
Let’s use a new term for the middle ground of indoors: mid-doors. Despite the lack of vocabulary, the mid-doors is quite common and includes many of our favorite urban spaces. Most mid-doors spaces have some elements fully controlled, while others are uncontrolled or partially controlled. Well-designed atriums—such as the originator of contemporary atriums, the Ford Foundation in New York—provide protection from rain and sound, but allow in more sunlight and allow more temperature fluctuation than a fully conditioned space. Grand European train stations provide protection from the sun and some rain at the platform, with an enclosed but mostly unheated waiting hall. Colorful covered markets protect from the rain and sun only. Indoor shopping malls fell out of favor, replaced by outdoor shopping centers, often with partially sheltered “streets.”


This is one of a series of articles about how the concept of “indoors” affects our built environment. Read more:

Why do Americans like it to be 72 degrees inside?

How does your office decide what temperature will make the most people happy?

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Artists began exploring and challenging our relationship with the indoors and outdoors a generation ago. James Turrell’s Skyspaces, for example, with carefully designed unprotected openings to the sky, exhibit feelings of both indoors and outdoors and celebrate a close examination of the changing sky. Random International’s hit Rain Room installation places visitors in a downpour without getting wet, and Transsolar—where I work—created a series of cloud installations that allow visitors to pass through and above an indoor cloud.

Random International’s 2012 installation Rain Room. [Photo: Flickr user Best international]
Architecture has always explored the potential of the mid-doors on a small scale, but intentional design for the mid-doors in commercial architecture is increasingly reserved for major cultural projects. The Shed in New York’s Hudson Yards includes a large-scale rolling structure that allows an outdoor plaza to be enclosed as a mid-doors or indoors space. The new Louvre Abu Dhabi has a massive perforated dome covering a plaza sprinkled with gallery buildings. Despite the lack of walls or air conditioning, the dome creates its own microclimate—a comfortable contrast with Abu Dhabi’s sun and heat. The plaza is reportedly as popular as the galleries themselves.

The Shed, NYC. [Photo: iStock]
Most North American buildings, though, lack spaces intentionally designed as mid-doors. Architects usually blame this on the engineers: the invention of air conditioning and engineering standards for temperature, sound, light, and more led to ever-more-rigid requirements, which building owners then insist on. While partially true, in the last 10 years many of these standards have become more enlightened, but the old stringent requirements maintain decades of momentum. Not all spaces have to be designed to meet these requirements, either. Would you enjoy having a discussion or lunch with a colleague or friend in a 60°F plant-filled winter garden in January?

New research also shows that there are explicit benefits to mid-doors spaces. So-called “biophilic” elements, like variation in temperature and airflow, presence of water, non-rhythmic sensory stimuli, and connections with nature have been shown to reduce stress, improve cognitive performance, and positively impact emotion and mood. All of these elements, coincidentally, are much easier to incorporate in mid-doors spaces than fully indoors space; it’s difficult to describe a mid-doors space without these characteristics. Besides the human benefits, mid-doors spaces provide energy savings. Relaxed temperatures result in less heating or cooling energy, or in some cases, no energy use at all.

Unfortunately, most building owners or developers still see mid-doors spaces as wasted space, not contributing to the functions of a building, so mid-doors spaces are rarely built, and when they are, they are treated as a luxury. Intentionally creating a diversity of useful spaces along the spectrum of indoors to outdoors can add value, reduce construction cost, and save energy, but only when seen as in place of other, “fully indoors” spaces, not in addition to. In our own practice we have only recently begun to encounter a new generation of building owners who share this perspective. Let’s hope for their success and look forward to cities filled with places to spend parts of each day mid-doors.


Erik Olsen leads the New York team of climate engineering company Transsolar KlimaEngineering. He is passionate about human comfort and low-impact solutions for our environment. Transsolar is widely recognized as a world-leading innovator in the field of high-performance buildings. In partnership with top architects, their unique approach has led to numerous breakthrough projects around the globe.

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