How do you design a building where neighbours become friends by accident?
Here is an uncomfortable pattern. Loneliness is rising fastest in dense, crowded cities, exactly where people are most physically surrounded by others. We live stacked on top of each other and still do not know the person across the landing. Architects design buildings for privacy, because that is what people say they want, and the privacy quietly comes with a side effect almost nobody asked for: isolation.
People want both, rest and connection, but when the design has to choose, it chooses rest every time. So the question worth asking is how you design a building that protects privacy and still makes neighbours into friends, without anyone having to make an effort. Some Danish apartment buildings answer it with a single design move.
What the shared walkway did
The move is a covered communal gallery, a shared walkway that every resident passes along to reach their own front door.[1] You cannot come and go without travelling the same route as your neighbours, which means you meet them, again and again, by accident. Not at an organised event, not through an app, just in passing, day after day. That repeated, incidental contact is the design tool. The neighbourhood evening is not.
And residents tend to experience this not as an intrusion on their privacy but as a gift. Their home is still private. The route to it is social. The building gives them both, by separating the two rather than forcing a choice.
Why this is design, not effort
It is easy to assume the residents who become friends are the ones who made the effort. The shared-walkway buildings show how much of it is simply the route. People who would never have organised a meeting, never knocked on a door, become familiar with their neighbours purely because the building keeps placing them in the same passage at the same times. No effort of will was required. The architecture did it.
Which means turning neighbours into friends is far less about anyone's sociability and far more about whether the building makes them keep meeting.
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The science: the power of passive contact
The principle here is the strength of passive contact: regular, incidental, low-stakes encounters between equals are among the strongest predictors of whether people form friendships, stronger than shared interests or compatible personalities.[2] It is not deep conversation that builds the bond at first. It is sheer repeated exposure, seeing the same face in the same place often enough that a nod becomes a greeting, a greeting becomes a chat, a chat becomes a relationship. Familiarity, built by repetition, does the early work.
This is why the communal gallery is so effective and the neighbourhood barbecue so weak. The barbecue is a single, high-effort, occasional event. The gallery delivers exactly what friendship actually grows from: small, frequent, effortless encounters, built into the route home. The building manufactures the repetition that relationships need.
Through a Behavioural Design lens: designing the encounter, not urging the effort
It is worth naming the discipline here, because the shared walkway is a clear example of designing for what cannot be willed. You cannot decide your way into knowing your neighbours; the familiarity has to accumulate through contact you mostly do not plan. Most attempts to build community ignore this and put the burden on the individual: the invitation to attend, the app to join, the effort to reach out, all of which compete with everyone's busy life and usually lose.
The communal gallery asks for no effort at all. It changes the situation so the encounters happen as a by-product of people simply going home. The behavioural design move is to stop urging people to connect and instead redesign the everyday route so that connection becomes the natural result of movements they are already making. The residents are not trying to be neighbourly. The building keeps introducing them, and familiarity does the rest. At SUE, the Influence Framework and SWAC are the methods we teach in the Behavioural Design Fundamentals Course to systematically analyse how design triggers connection rather than leaving it to chance.
What this means in practice
Start with the passive contact already shaping your own life. The people you feel easiest with are very often simply the ones you see most often by routine, not the ones you have made the most deliberate effort over. If there is a relationship you want to warm up, the highest-leverage move is frequency, finding small, regular, low-pressure ways to cross paths, rather than one big effortful gesture. Repetition builds warmth more reliably than intensity.
For anyone leading a team, this is a practical lever for connection and trust. Big offsites and structured team-building are the high-effort, occasional barbecue. What actually builds a team is frequent, low-stakes contact: the brief regular check-in, the shared space people pass through, the routine that keeps the same people meeting. If a team feels distant, especially a remote one, the answer is rarely a grander event. It is engineering more frequent, lighter touchpoints into the ordinary week.
And at the level of the organisation, this reframes how you think about connection across distance and structure. When the everyday passages that produce passive contact disappear, fully remote work, siloed departments, buildings designed so nobody need meet, relationships stop forming on their own and have to be deliberately re-created. The skill this teaches is to treat incidental contact as something you design into the routine, not a nice accident you hope for, because it is where trust quietly begins.
Learn to apply this yourself
What makes the shared walkway effective is that connection is built into the route rather than added on top of it: the situation produces the behaviour without requiring any effort or motivation from the individual. In the Behavioural Design Fundamentals Course, you learn to use the Influence Framework and SWAC to map exactly these kinds of situational forces and redesign them so the desired behaviour becomes the path of least resistance.
View the Behavioural Design Fundamentals CourseWhat you can design this week
You will not be adding a communal gallery, but the underlying move works on any relationship or group you want to warm up. Three ways to start:
Choose frequency over intensity. Passive contact builds warmth through repetition, not through one big effort. Engineer small, regular, low-stakes ways for people to cross paths rather than relying on the occasional event.
Build connection into the route, not on top of it. The gallery works because it is on the way home. Put the contact where people already go, a shared route, a regular touchpoint, rather than asking them to make a special effort.
Separate privacy from isolation. People want rest and connection both. Design so the private space stays private but the route to it is social, rather than letting a desire for privacy quietly produce isolation.
The Danes did not make their residents more outgoing. They built a route home that kept neighbours meeting, and let familiarity turn them into friends. That is the difference between organising connection and designing for it, and it works on a friendship, a team or a whole building.
Want to learn to read a space for what it does to the people inside it, and design it on purpose? That is the heart of our Behavioural Design training. Details on the SUE website.
Frequently asked questions
Why does the shared walkway produce friendships when organised social events usually don't?
Organised social events are high-effort, occasional, and attended voluntarily, which means the people most likely to benefit from connection are often the ones least likely to show up. The shared walkway works because it requires nothing: every resident passes through it simply to reach their own front door. The contact accumulates through sheer repetition, dozens of brief, incidental encounters over weeks and months, and it is that repetition, not a single well-intentioned evening, that builds the familiarity friendship actually grows from. The barbecue is an event. The gallery is a route.
What is passive contact and why does it build relationships?
Passive contact refers to regular, low-stakes, incidental encounters between equals, the kind that happen as a side effect of shared proximity rather than through deliberate effort. As the article notes, drawing on Festinger's work and later research, this type of repeated exposure is among the strongest predictors of friendship formation, stronger than shared interests or compatible personalities. A nod becomes a greeting, a greeting becomes a brief exchange, and an exchange becomes a relationship, without anyone having decided to befriend anyone. Familiarity, built by repetition, does the early work that people usually attribute to chemistry or effort.
How can a remote team apply the passive contact principle without a shared building?
The building principle translates directly: stop relying on the occasional offsite or team-building event and engineer more frequent, lighter touchpoints into the ordinary week. A brief regular check-in, a shared digital space people pass through daily, a standing short call at the start of the week, these are the remote equivalent of the communal gallery. The goal is not one deep encounter but many shallow ones, because it is frequency that builds warmth, not intensity. If a remote team feels distant, the answer is almost never a grander event.
Why did residents not experience the shared walkway as an intrusion on their privacy?
Because the design separated the social from the private rather than conflating them. The front door still leads to a home that belongs entirely to the resident; the walkway is on the way to it, not inside it. Privacy and connection were not forced to compete for the same space. This is the distinction the article treats as the design insight: not that people must choose between rest and connection, but that a building can provide both by placing them in different locations. When the social encounter is on the route rather than in the home, it reads as a gift rather than an intrusion.
If you want to learn how to design for behaviour rather than trying to motivate it, that's exactly what the Behavioural Design Fundamentals Course covers. View upcoming dates →
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