Circulation is the only floor in a house that nobody asks for. It appears because the rooms have to be reached, and because it appears late in the design it is usually paid for by whichever room was drawn last. Budgeting it at the start is what stops that.
What counts as circulation
Any floor whose only job is getting you somewhere else. That is the entrance hall, the corridors, the landings, the stair and the opening it needs in the floor above. Two things that are commonly miscounted:
- The route across a living room does not count. That floor is doing two jobs, which is precisely why an open plan spends less on circulation. It is also why the route has to be drawn: a living room crossed by the only path to the kitchen is circulation wearing a sofa.
- The stair counts, on both storeys. The flight occupies the lower floor and the opening occupies the upper one. A stair is usually the single largest piece of circulation in a house, which is why its position decides the percentage more than any corridor does.
The shares
| Plan | Share of net area | What it looks like |
|---|---|---|
| Compact open plan | 8–10% | Rooms open off the living space; the only real corridor serves the bedrooms. |
| Ordinary house | 10–15% | A hall, a landing and a short corridor. The figure to design to. |
| Accepted upper limit | 15–20% | A long plan, a wide accessible corridor, or a third storey. Deliberate, not accidental. |
| Too much | over 20% | A room's worth of floor is being walked on. Change the arrangement, not the room sizes. |
These are proportions of the net area, meaning the floor inside the walls, not the gross footprint. Walls themselves take a further 4 per cent or so of a normal house, which is a separate deduction and covered in the allocation guide.
What that is in square metres
| Net area | Circulation budget | Typical house | What it has to buy |
|---|---|---|---|
| 60 m² | 5–9 m² | 2-bed flat | One hall. A corridor at this size is a corridor too many. |
| 80 m² | 6–12 m² | 2-bed house | Hall plus landing, or a single 4 m corridor. |
| 100 m² | 10–15 m² | 3-bed house | The size where a badly placed stair costs a bedroom. |
| 150 m² | 15–22 m² | 4-bed house | Two storeys of landing; watch the upper corridor. |
| 200 m² | 20–30 m² | Large house | Wings and a stair hall. Circulation becomes architecture here. |
Notice that the budget grows more slowly than the house. A 200 m² house does not need three times the circulation of a 60 m² flat, because the number of rooms to reach grows faster than the distance between them. A large house that spends 20 per cent on circulation is not big, it is badly organised.
A corridor costs a square metre per metre
This is the arithmetic that makes the percentage real. A corridor's area is its width times its length, so at a metre wide every metre of it costs a square metre. Run a corridor 6 m down the middle of a plan and it has taken 6 m², which is most of a single bedroom.
| Corridor width | Per metre | 4 m long | 6 m long |
|---|---|---|---|
| 900 mm | 0.9 m² | 3.6 m² | 5.4 m² |
| 1000 mm | 1.0 m² | 4.0 m² | 6.0 m² |
| 1200 mm | 1.2 m² | 4.8 m² | 7.2 m² |
| 1500 mm | 1.5 m² | 6.0 m² | 9.0 m² |
Read the table across rather than down. Widening a 4 m corridor from 900 to 1200 mm costs 1.2 m², and it buys a corridor two people can pass in. Shortening that same corridor from 6 m to 4 m saves 2 m² at any width. Length is where the waste lives, not width, which is why the answer to a circulation problem is almost never a narrower corridor.
What moves the figure
Five things decide the percentage, and only one of them is the corridor's width.
- Where the entrance is. Entering the middle of a plan halves the longest route. Entering at one end guarantees a corridor the length of the house.
- Where the stair is. A stair in the middle lands the upper floor in the middle too, so both storeys are served by short landings. A stair at the gable end produces two long corridors, one above the other.
- How many rooms a single space serves. A hall with four doors off it is one piece of circulation doing four jobs. A corridor with one door at each end is the opposite.
- Whether rooms are on one side of the corridor or both. Rooms on both sides halve the corridor per room, which is why single-aspect plans are efficient and why a corridor with a blank wall down one side is the classic waste.
- Storeys. Every extra floor adds a landing and a stair opening. A three-storey house on a small footprint spends heavily on circulation and gets a small garden in return.
Measuring it on your own plan
Add up the areas of the hall, the corridors, the landings and the stair opening, then divide by the net floor area of the storey. Two rules make the number honest:
- Do it per storey, not just for the house. A ground floor at 9 per cent and an upper floor at 22 per cent average to a healthy 15 and hide the problem entirely.
- Count the floor, not the intention. A 1.4 m stretch of hall that holds nothing is circulation whatever it is labelled, and a dead-end 800 mm behind a door is circulation that does not even circulate.
In Gridsnap, name the areas Hall, Landing or Corridor and
each one reports its own m² in the properties panel. Naming them also arms the plan check's
900 mm minimum width on those rooms, which an unnamed corridor never gets.
When the figure comes out too high
Over 20 per cent is a message about the arrangement. Do not answer it by narrowing the corridor to 800 mm: that saves a fraction of a square metre and makes the house worse to live in. Answer it by shortening the route, which is a plan change. The moves are set out in how to reduce wasted hallway space, and the biggest of them is moving the entrance or the stair, not the walls of the corridor.
And when it comes out very low
Under 8 per cent usually means one of two things, and only one of them is good. The good one is a genuinely open plan where the living space is the circulation, with the bedroom doors grouped off a short hall. The bad one is a plan where the route runs through rooms that should have been private: a bedroom you cross to reach a bathroom, or a kitchen that is the only way to the garden. That plan spends no floor on circulation and pays for it every day instead.
The widths themselves are a separate question with harder numbers, covered in how wide should a hallway be.