III. Ordinary Things Essay 17
A Staircase Is a Rule Made of Wood
Consistency, accidents, and the rules that follow them
You go up the stairs at a speed, and you arrive at the top without having thought about a single step. You did not count them. You did not look down. Your foot found a rhythm and your body used it, and the rhythm was not in your head. It was in the shape of the stair itself, and the stair had been built so that the rhythm would be there.
Here is what a staircase is. It is a set of risers and a set of treads, and the rule that makes it a staircase rather than a pile of blocks is that the risers are the same height and the treads are the same depth. That is all. One number, repeated. The whole design problem of a staircase is the choice of that number, and the number is a rule, and the rule was arrived at in a way that is worth understanding.
A staircase is a principle that has been cut out of wood. Somebody worked out a general rule about how people walk, and then built a thing that enforces the rule, and the rule is now so built in that you cannot see it while you are using it. The stair does not tell you how to walk. It makes walking the obvious thing.
You are on a staircase in a building you have never been in before. The first flight has a step height your leg gets used to. You take five steps and you have it, you know the rise, you know the tread, and your foot is already timing itself for the sixth. Now you turn onto a second flight, in the same building, and the steps are slightly different. Shallower, or steeper, or a different depth. And you have to look, and you have to re-find the rhythm, and for a moment the walking is conscious work again.
Now change the condition. The second flight has the same steps as the first, which is what happens in most buildings, because the same number is cut once and used for the whole building. And the re-finding does not happen, and you arrive at the top of the second flight having paid no attention to it at all. What you have saved is not energy. It is attention. The stair has done the arithmetic for you so that you can spend your attention on the conversation you are having.
And now change a different condition. What if the building has a small deliberate change partway up, a step that is a different height from all the others, the kind of thing that is sometimes put in to make people look up? The rhythm breaks. A person who was walking without attention now has to attend. The whole flight gets slower, because the person is now on the concrete level for a moment, counting and checking, and the concrete level is expensive.
What the rule is for
It is worth being precise about what the equal-riser rule is actually for, because the obvious answer is wrong. The obvious answer is that it is for safety, and it is partly for safety, but safety is not the whole thing and it is not even the main thing.
A step that is too high is a trip hazard, because the foot arrives expecting a certain height and does not find it. A step that is too low is worse, and less obvious, because the foot has to do extra work to climb it, and a person carrying something heavy is doing that extra work without knowing why. A tread that is too shallow means the foot has nowhere to land properly and the shoe catches the riser. A tread that is too deep means the foot can get lazy about where it lands, and a person who is looking at their phone will land short.
So the rule is: make the stair regular enough that the foot can run on autopilot. That is the actual purpose. The rule is about rhythm, and the rhythm is about freeing up attention, and the safety is a consequence of the rhythm rather than the other way round. A stair with equal steps is a stair you do not have to think about, and a stair you do not have to think about is a stair you cannot fall down, because falling is what happens when you are thinking about a thing you should not have to think about.
This is why the anomalies are so effective. A single uneven step in a flight of even steps is not a small nuisance, it is a reset. Everything you had learned about the flight is voided, and you have to learn it again, and people do not learn flights, they learn rhythms. One odd step costs the whole flight.
Rules that come second
Now the part that connects this to the rest of the site, which is where rules come from.
Most of the rules we live by were not designed. They were written down after something happened. Somebody fell on a stair, or somebody fell off one, and a group of people decided that this would not happen again, and the decision took the form of a number, and the number was cut into a piece of wood and installed in a building.
That is a principle in the sense used earlier on this site. It was distilled from cases. It was generalised from what happened to something that applies in cases that have not happened yet. And it has a scope, which is the set of circumstances in which the fall happened, and the scope is invisible in the rule itself.
And this is why the case should be kept. A rule with its case attached can be asked whether it still applies. A rule with its case deleted can only be obeyed or resented, and those are the two options available to everybody who meets it and cannot see why it exists.
Scope and the case next door
The rule built for a fall on a stair says nothing about a staircase where nobody has ever fallen. It says nothing about a ramp, or a ladder, or a slope, or a flight on a boat, where the floor moves. The rule is about a specific kind of arrangement, and the arrangement is not stated in the rule.
And there are cases where the rule is actively in the way. A person with a bad knee wants a shallower step. A person who is carrying a heavy load wants a shallower tread so they can see where they are going. A person with a walking frame needs a landing halfway up. Every one of these people is asking for a departure from the rule, and every one of them is asking for it because the rule was written for a case that was not theirs.
And the rule itself has a case that is easy to forget: the person who fell. The rule is a memorial to somebody's bad afternoon, and memorials are treated with a respect that is partly about the person and partly about the fact that we do not want to think about what it takes for a rule to become optional. A rule that people can quietly depart from when it does not suit them is a rule that people will quietly depart from when it does not suit them, including on the flight where it very much does.
What if a building had two staircases, one with the standard steps and one with shallower ones? Every standard stair is a bit faster for most people, because the rhythm is more familiar, and the familiarity is worth about half a second per flight. But the shallower stair is the one nobody falls on, and it is the one a person with a pram or a heavy bag or a stiff knee will take every time, and it will be the one that a visitor with a suitcase takes by mistake, because it looks the same.
Now change the condition. What if instead of two stairs, every stair were the shallower one? Everything gets slightly slower and everybody is slightly safer, and the extra fraction of a second per flight is now paid in aggregate by everybody who uses the building all day. Whether that is a good trade depends entirely on how many people use the stair and how heavy the loads are, and it is exactly the kind of question that the standard step height, being a single number everybody uses, has quietly answered without anybody asking.
"Building regulations are arbitrary, so they can be ignored." They cannot, and the reason is interesting. A regulation is a principle that has been written down in a way that nobody can argue with, which is convenient and also removes the case. The number is there because a specific set of people looked at specific accidents and chose a number. The number is not arbitrary. It is a generalisation that has been frozen, and frozen generalisations stop carrying their reasons.
The other misconception: "safety rules are about the edge cases." They are about the ordinary case, overwhelmingly. The number of steps is chosen so that the great majority of people, on the great majority of days, carrying the great majority of things, can use the stair without thinking about it. The edge case is protected by the rhythm of the ordinary case, and when the rhythm breaks the edge case arrives immediately.
Rules in other materials
The staircase is one of the clearest instances of a general pattern, and the pattern turns up wherever a rule has to be enforced without anybody enforcing it.
A rule that is carved into wood is a rule that survives. A sign on a wall, a symbol on a button, a sound that everybody recognises, a number on a ruler, the shape of a key, the number of pins on a plug. Each of these is a way of making a general rule present in the environment so that the person who has to follow it does not have to remember it and does not have to understand it. The rule is carried by the material.
And the material version is better in one specific way, which is that it applies at the moment of action rather than at the moment of decision. A sign at the bottom of the stairs tells you to hold the rail on the way up, when the hand is on the rail. A memo about the rail, read in an office in the morning, is a rule about a decision you will not remember making on a staircase in the dark.
A staircase is the most literal version of that, and it is why stairs are the first thing people learn about a building and the last thing they notice. You never think about the stair. You think about the thing you went up the stairs for. The rule has done its work and retired from the conversation, which is the best possible outcome for a rule and is also what makes it hard to argue with.
Limits
This essay does not state any specific dimension for a stair, and that is deliberate. The numbers in building regulations are jurisdiction specific, they change, and they are revised in light of evidence, and stating one here would be stating a fact that this site is not in a position to check. The general shape of the argument, that a repeated number produces a rhythm and the rhythm produces safety, does not depend on which number it is.
Second limit: the argument is that regularity helps, and it is possible to over-regularise. A building where every stair is identical, every corridor is identical, and every room is the same is a building where you cannot tell where you are, and people get lost in buildings like that, and being lost is its own kind of hazard. There is a version of this essay that says uniformity is always good, and that version is wrong.
Third limit: a staircase is one kind of arrangement, and the reasoning transfers badly to arrangements where the users are not bodies on feet. A timetable can be regular and still be a disaster for the people in it. The mechanism is different, and the word regularity is doing more work than it should if it is carried across without checking.
Stuck
You are stuck at the tangible level with a staircase when you are still measuring steps. You are counting risers, checking depths, comparing a tread with a drawing, and none of it is going to change anything, because the number is not the problem and the number was never the problem.
The way out is to change the thing the number is for. If the concern is falls, then go and look at what falls, on this stair, and when, and who. The useful information is in the events, not in the geometry. If the concern is speed, then count the seconds, on this stair, for this person, and do not generalise. If the concern is access, then find the person who cannot use the stair, and ask what they need. In every case the number stops being the subject and becomes the evidence.
Sources
- No specific dimension, regulation, standard, date, or study is cited in this essay. The general point about consistent riser heights producing a learnable rhythm is offered as an explanation, not as a technical claim.
- All examples are ordinary situations described from general experience rather than from a documented case.