Buildings usually have a front door.

At home, it’s the door you pose in front of with your new bike / puppy / degree / wife / baby / grandchild. In public buildings it’s the set of stairs on which politicians erect podiums, it’s the setting of countless wedding photos, of protests, celebrations, demonstrations and proclamations. It’s the part of the building that’s trying to say and do the most things, to tell you something about what to expect on the inside, but also to project something outwards, to wear the make-up and the jewellery.

I’m more interested in the back doors.

The service stairs, the fire escapes, the corridors and carparks. The places designed to perform simple tasks with simple means. The places where singularity of function creates a paucity and austerity of form that rivals the minimalism of Judd or Flavin.

Walt Disney Concert Hall. Photo by Sally Hart

Barbican. Photo by Sally Hart

Their lack of ornament renders them sculptural, their unadorned walls provide a blank canvas for un-designed activity. Their functional role is so rarely enacted that they become magnets for the unplanned, the spontaneous, the dingy, the dirty, the dangerous. They’re stumbled down, and hidden in. They protect and conceal. They’re the scene in every film where a shadow needs to loom, where a tryst needs to happen at midnight, where a non-descript suitcase needs to be passed from hand to hand.

They’re vessels for the unexpected and they’re beautiful.

National Theatre. Photo by Sally Hart