Blurring the Lines with Mid-Door Spaces

Client-focused solutions create value while reducing costs and saving energy

As the architectural critic Beatriz Colomina describes in her book X-Ray Architecture, the beginning forms of Modernism can be seen as a reaction to the fear of tuberculosis, which was rampant in the 1920s. This architectural response was defined by clean, white, open spaces that became iconic and filled with fresh air, as exemplified by Alvar Alto’s Paimio Sanatorium and others.

Similarly, COVID-19 affected all of us and changed how we experienced our personal lives, communities, and workspaces. COVID-19 altered spaces by adding walls and creating defensive zones within spaces. Another byproduct of this pandemic was the desire for more open and partially outdoor spaces where fresh air would support a required level of hygiene. This development led some building owners to rethink the use of terraces and even modify their exterior building skin to let in more air. Maybe something between the enclosed, fully heated interior spaces and the wide-open outdoor ones could exist, much like many of the train stations and outdoor markets in Europe have for hundreds of years. However, some heating and cooling are required in the Northeast for spaces to be comfortable year-round. This necessity has led to the adaptation of building enclosures to be more permeable and flexible.

The name for this new typology – literally the middle space between indoors and outdoors – is Mid-Door spaces, and they require new materials that use properties of flexibility. The spaces can be enclosed in the colder months but open and outdoors in the warmer ones; high translucencies are used to create these temporal enclosures that feel like an outdoor sunroom. Mid-door spaces offer protection from the elements but invite in more sunlight and allow more temperature fluctuation than indoor spaces. And they can offer a calming, nature-filled break from dull offices. Often, the floor-to-area ratio, or FAR, is not affected by these demountable enclosures, which are understood by building officials to be seasonal rather than permanent. This allows for greater flexibility in the programming of spaces and potentially allows for additional rooftop floors.   

One reason this adaptation now exists is because of new materials. These materials include lightweight fabrics with translucencies of up to 65%. They can be tensioned to resist wind and snow loads, much like a high-tech tent. Sometimes, higher translucencies are desired, and transparent Ethylene Tetra Fluoro Ethylene (ETFE) foil membranes, which have been used for greenhouses for many years, are employed. The foil membranes are used as inflated pillows or cable-reinforced sheeting, where the cables become the primary structural support. The pillow version can be made of multiple layers, which have insulative qualities equivalent to thermal glazing panels but with a carbon footprint 80% lower than that of glass. Their strength is that they are operable systems with open and close wall units, allowing for greater ventilation.

Two projects we recently completed in the Times Square area of New York City are examples of this approach. One is at a new hotel called the Times Square EDITION, and the other is the new TSX Building. Both had outdoor spaces that building management wanted to incorporate yet maintain a sense of the outdoors. 

At the EDITION, we developed an ePTFE (expanded polytetrafluoroethylene) tensile membrane with a 20% translucency suspended between steel tree-like columns incorporating diffuse lighting at the framing nexus. Below the roof membrane, operable glass doors can be opened to create a shaded outdoor space or enclosed to be heated and cooled in intense thermal conditions.

For the TSX project, we used a clear ETFE pillow system as the roof and motorized sliding ETFE wall panels, which can open or close according to the weather conditions. The enclosed dining areas become outdoor rooms at the push of a button.

Rather than thinking of indoors and outdoors as a binary condition, we want building owners and their management teams to understand there is a spectrum, and creating a diversity of useful spaces along this spectrum of indoors to outdoors can add value, reduce construction costs, and save energy. This is an exciting new paradigm that’s here to stay.