Zoning and the Myth of Separation#
SLOP2418 — Urban Design Studio
Week 3 · Marisol Quaye · 8 March 2027
direct readout · derived measure · worked hypothetical
The question this week#
You have a block layout. You now have to say what goes in it.
- Every cell you paint names a use. There is no neutral option in the palette.
- Separating uses removes a nuisance and adds a distance.
- Mixing uses removes the distance and returns the nuisance.
- The question is not which is correct. It is which cost your district is better able to carry.
1898: separation as public health#
- Howard’s garden city arranged uses in concentric rings, with the factories on the outer ring and the housing held clear of them.
- The diagnosis was correct for the conditions: coal smoke, untreated effluent, and no mechanism to control either at source.
- Separation was not, at that point, a preference about neighbourhood character. It was a way of not dying.
- Attribution: Ebenezer Howard, To-morrow: A Peaceful Path to Real Reform (1898).
1926: separation becomes law#
A nuisance may be merely a right thing in the wrong place, like a pig in the parlor instead of the barnyard.
— Justice Sutherland, Village of Euclid v. Ambler Realty Co., 272 U.S. 365 (1926)
The court upheld comprehensive use zoning as a valid exercise of the police power. Almost every zoning code written since is a descendant.
What the Euclidean code actually did#
The classic arrangement, set as a descending list, most protected at the top:
| District | Permits | Excludes |
|---|---|---|
| U-1 residential | Single dwellings | Everything below |
| U-2 residential | Dwellings, two-family | Commerce and industry |
| U-3 commercial | Shops, offices, and the above | Industry |
| U-4 light industry | Light manufacture, and the above | Heavy industry |
| U-5 heavy industry | Everything | Nothing |
The code is a pyramid. Protection accumulates upward, and so does distance from work.
1929: separation at neighbourhood scale#
Traffic stays outside; school and open space sit at the centre.
1961: the case against#
- Jacobs’s first condition for diversity: a district must serve more than one primary function, so that people on different schedules are present at different hours.
- A district with one function has one schedule. It is full for two hours and empty for twenty-two.
- The consequences she names are livability consequences — surveillance of the street, the viability of small enterprise, whether anybody is about at nine in the evening.
- Attribution: Jane Jacobs, The Death and Life of Great American Cities (1961).
2000: regulate form, not use#
- Duany, Plater-Zyberk and Speck argue that codes should control what a building does to the street — height, setback, frontage, parking placement — and leave what happens inside it largely alone.
- The claim is that most of what separation was protecting was really form, and that use was a crude proxy for it.
- The claim’s limit: form-based codes are weakest exactly where separation was strongest, which is airborne and waterborne nuisance.
- Attribution: Suburban Nation (2000).
A hundred and two years, in one line#
1898 keep the smoke away · 1926 and here is the law · 1929 and here is the neighbourhood · 1961 but nobody is on the street · 2000 so regulate the building, not the business
The palette you actually have#
- Residential by density — low, medium, high — plus row housing and mixed housing, which puts commerce beneath dwellings in one cell.
- Commercial, low and high density. Office. Industry.
- Cells attach to road frontage to a limited depth, so the block layout chosen in Week 2 has already decided how much of each you can paint.
- Districts are painted over the top, and scope tax rates and policies to an area rather than to a use.
This is a use-based code with one mixed-use exception. Euclid would recognise it.
Two schemes for Halstead Reach#
Both schemes use the same block layout and house the same population.
| Measure | Scheme A — separated | Scheme B — adjacent |
|---|---|---|
| Residential | The terrace, north of the rail line | The terrace, north of the rail line |
| Commercial | One strip on the collector, at the quarter’s edge | Mixed housing on the two main frontages, plus corner cells |
| Industry | Ombersley Flats, 3.2 km south-east, across the Kerrow | Eastern edge of the Reach, 0.8 km from the nearest dwelling |
| New infrastructure required | One river crossing, one arterial to it | None beyond the quarter’s own streets |
| Home-to-work trip, typical | 3.2 km, one crossing, one route | 0.8 km, several routes |
| Pollution exposure at dwellings | Effectively none — downwind, downstream | Measurable ground and air footprint on the eastern blocks |
Where the pollution goes#
Siting changes exposure; zoning colour alone does not.
Where the trips go#
The same two schemes, read on the traffic volume overlay at 08:00.
| Measure | Scheme A — separated | Scheme B — adjacent |
|---|---|---|
| Work trips crossing the collector mouth | All of them | About a third |
| Routes available for the work trip | One, via the crossing | Three or more, depending on Week 2’s block dimension |
| Peak volume on the busiest link | High and concentrated in two windows | Lower and spread |
| What fails first | The crossing | Nothing yet; Week 6 will find it |
| Fixable later by | Transit — Week 5 | Not obviously anything |
The tradeoff of the week#
Separation buys livability with mobility performance. Every metre you put between the housing and the work is a metre somebody walks, drives or rides, twice a day, for the rest of the semester.
- Scheme A: no pollution at the dwellings, 3.2 km and one crossing.
- Scheme B: 0.8 km and several routes, a measurable footprint on the eastern blocks.
- The memo names which you chose, what it cost, and what you intend to do about the cost.
Before Tuesday, and Assessment 1#
- Build both schemes. Use a sandbox save for the second one; sandbox saves are never marked and are the fastest way to find out how a system behaves.
- Bring four screenshots: ground pollution and traffic volume, at 08:00, for each scheme.
- Bring the home-to-work distance for one named dwelling under each scheme. One dwelling, named, both schemes.
- Commit to one scheme in your assessed save before Week 4.
- The Assessment 1 brief is issued this week. Neighbourhood Unit Plan, due Week 4, 25% — fiscal 30, mobility 30, livability 40. Read Perry again before you read the brief.
- Save as
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