Alec Nevala-Lee

Thoughts on art, creativity, and the writing life.

The hotel bathroom puzzle

with 17 comments

The bathroom at the Hotel Louis XIV

In his wonderful book The Evolution of Useful Things, the author and civil engineer Henry Petroski shares one of the most famous case studies in the history of design:

Before it was destroyed by fire, L’Hotel Louis XIV, which was located on the waterfront in Quebec, advertised private baths. However, their privacy was of a limited and precarious kind, for each bath was located between a pair of guest rooms, both of which opened into it. This arrangement is not uncommon in private homes, where bedrooms share a bathroom or where a bathroom opening onto a bedroom also opens into a hallway. In all such situations, the basic design objective is to achieve privacy for whoever might be using the bathroom. This can be achieved in many ways, of course, and the most obvious and common way is to have locks on each of the doors, so that the bathroom user may bar others from entering. The failure of this solution is frequent and frustrating: the person who has finished with the bathroom forgets to unlock the second door, causing at least a little inconvenience for the next user who tries to enter it. In bathrooms shared by siblings, screaming through the locked door may or may not get results, but generally there is little more than the temporary inconvenience of having to go around to the other door or to another bathroom in the house. Families that find bathroom doors too frequently locked can remove all locks from the doors and trust everyone to knock before entering.

“In the case of bathrooms shared by unrelated guests,” Petroski continues, “the problem is less easily solved.” Consider, for example, the hotel bathroom shown above. There are two doors, each opening into a separate room occupied by a guest who is presumably a stranger to the other. You need locks on both doors to ensure privacy for each occupant, which means that you’ll invariably wind up with situations in which one guest leaves and forgets to unlock the second door, leading to considerable inconvenience. What do you do? You could, of course, tear down and rebuild the entire hotel, at great expense, so that each room has its own bathroom—a solution that might sound ridiculous, but isn’t so far removed from how similar design problems are addressed every day. More plausibly, you could somehow label the doors. Petroski notes that this was the approach employed by a similar house in which he once stayed in St. Louis: “The measures taken to avoid this situation consisted of a nicely printed sign placed prominently on the dresser beside the bathroom door, reminding each guest to unlock the other guest’s door before leaving the bathroom. I am sure I was not the only guest who suffered from the inadequacy of that solution.” Alternatively, if you were of a mechanical disposition, you could rig up an alarm system that would sound a buzzer if one door was unlocked without the other. This would have obvious shortcomings in practice, and it would also annoy guests who just wanted to use the bathroom in peace.

The bathroom at the Hotel Louis XIV

In the end, the proprietors of the Hotel Louis XIV came up with an ingenious answer, as outlined in the book By Design by Ralph Caplan, which was Petroski’s source for the original case study:

Well, there were no locks on the bathroom doors of the Louis XIV, but tied to each doorknob was a three-and-a-half foot length of leather thong to which a hook was attached. When you were in the bathroom you simply linked the two hooks together, holding both doors shut. There was no way to get back into your own room without it at the same time unlocking the door for the other guest. It was memorable as the total integration of object and circumstance.

It’s a lovely solution—so much so, in fact, that Caplan’s book puts it into its own subtitle: Why There Are No Locks on the Bathroom Doors in the Hotel Louis XIV. And at the heart of the answer lies a subtle change in the way the problem is understood. Other measures, like putting up a sign, focused on the idea that both doors had to have locks, when the lock is really just an interim solution to the underlying problem, rather than the problem itself. As Petroski puts it: “The basic design objective is to achieve privacy for whoever might be using the bathroom.” And once the problem is phrased in such a way as to leave locks out of the equation entirely, you’re that much closer to figuring out how to address it.

And it’s a lesson that writers or other creative artists should take to heart. In On Directing Film, David Mamet devotes what seems like an inordinate amount of time to teaching his students how to properly describe the objective of a scene, and reminding them how easy it is to confuse the means with the end. One of the pitfalls of figuring out a plot is that once we’ve come up with a “solution” to a problem, like putting locks on the doors, we spend all our energy trying to get out of all the new complications that the solution presents, rather than focusing on the issue that it was meant to satisfy. In many cases, like the proprietors of the rooming house in St. Louis, we end up affixing a label to explain what we mean, which is as close as you can get to unambiguous evidence that the solution you have in mind isn’t working. Donald Norman, in his classic book The Design of Everyday Things, provides examples of the labels we see on everything from doors to to hot and cold water faucets, and concludes: “When simple things need instructions, it is a certain sign of poor design.” And that’s as true of stories as of sinks. Whenever a movie gives us an introductory scroll of text, a lingering shot of a sign, or a chyron to explain where we are or how much time has passed, it signals that the underlying problem hasn’t really been solved. If you want to find the right answer, you have to start by asking the right question. And then you can soak in the tub until you’ve figured it out—as long as you remember to lock the door first.

Written by nevalalee

November 27, 2015 at 9:40 am

17 Responses

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  1. It was great to read the article. Thanks for sharing.

    Sharon Reams

    May 22, 2017 at 5:51 am

  2. Cool stuff you have and you keep overhaul every one of us. Professionally I am a blogger and used to write at:

    Richard Dixon

    February 11, 2018 at 4:30 am

  3. Thanks for sharing the informative article. I got confused by reading the title but it was cleared at the body.

    Caroline Garcia

    April 17, 2018 at 5:41 am

  4. Motion detection in the bathroom that automatically locks/unlocks both doors (Able to open from inside bathroom.)

    When no motion is detected for awhile it turns off lights first. If still no motion is detected, it will unlock both doors.

    Problem solved.


    July 15, 2018 at 3:17 am

  5. Very neat and simple solution.


    July 15, 2018 at 7:07 am

  6. Dijkstra also has a bathroom story. Similar but different. There may be a pattern here…
    See here.


    July 15, 2018 at 8:24 am

  7. This method fails to allow emergency access should the occupant become unconscious, or if a child were to overflow the tub.

    Were the knobs themselves designed to allow them to be quickly removed?

    Steve Thompson

    July 15, 2018 at 12:42 pm

  8. Obviously hotel staff will have access through nfc card or regular emergency key. Child would first have to close the door for it to lock. If the child is able to close the door, it’s surely able to lock a door as well. Like in any hotel room, it again loops back to hotel staff.

    Knobs on outside of bathroom will open the door if it’s unlocked.
    Knobs on inside of bathroom will open and unlock the door.

    Nice try Steve. Just didn’t want to point such stuff out. As it would have been obvious solution.


    July 15, 2018 at 3:03 pm

  9. @Steve Thompson: I don’t know if this was true of the actual hotel, but since the only real concern is short-term privacy, it doesn’t seem too hard to design the connectors—or even the thong itself—to withstand a casual tug, but give way to a prolonged pull in case of an emergency.


    July 15, 2018 at 3:11 pm

  10. hewhotypes: I love this—thanks!


    July 15, 2018 at 3:11 pm

  11. @Sim – I was talking about the case where the two knobs are tied together from within the bathroom as in the Hotel Louis XIV.

    Nothing you said would make sense in that case. I suspect that you thought I was replying to your earlier comment, I wasnt.

    My comment was meant to warn people that the glib, simple, and obvious answer is often wrong for less than obvious reasons. This story is great, but in the United States this would be illegal, and for good reason.

    Steve Thompson

    July 15, 2018 at 6:04 pm

  12. It is a very nice trick, but I don’t believe it provides a true solution to the privacy problem. While the guest in each room can be confident of privacy while in the bathroom, both occupants gain unfettered access to both rooms when the bathroom is not in use. This situation is radically worse from a privacy perspective than a private room with a non-private bathroom. It is a private bathroom with non-private room!

    Bonobo Gris

    July 15, 2018 at 10:57 pm

  13. @Bonobo Gris You would have a totally ordinary lock on the bedroom side of each bathroom door. Something functionally equivalent to


    July 16, 2018 at 12:53 am

  14. This is a neat and simple solution for the type of doors that open into the room. But what about doors that open into the bathroom? The aforementioned thong will not be of use here. Any ideas?

    Carolina Thomson

    July 18, 2018 at 10:23 pm

  15. @Carolina Thomson: According to a commenter on Hacker News: “I visited some dorm rooms in Croatia once, and they had a nice solution to this problem. Both doors opened inward, with the non-hinge side of the doors sitting very close to one of the walls with no doors. Instead of a conventional lock, a narrow piece of wood ran the length of this no-door wall that could be rotated to block both doors simultaneously.”


    July 19, 2018 at 6:51 am

  16. And no one has mentioned how annoying a leather thong in the middle of a probably small bathroom would be. Would we be playing limbo? People who have poor balance (elderly, disabled, people carrying small children, drunk) would have problems especially if the floor is wet from recently getting out of the tub. Most solutions cause a new problem.


    December 16, 2020 at 12:13 am

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