NB: I believe this topic has been discussed much better many times elsewhere on the net and in print. I am writing simply to clarify my own thoughts. I apologize for the primitive graphics.
Over a number of posts I have discussed block sizes for progressively smaller blocks and denser housing arrangements. In the last one on the topic, I looked at smaller multi-unit buildings, and found that they continue to fit well into the 260' deep by 580' long (buildable area) block I have been using in my images and calculations for several posts. I this post, I will examine perimeter apartments, which is a common arrangement in European countries such as Sweden, Germany, and Czechia.
Perimeter apartments are arranged into perimeter blocks. These are distinct from courtyard buildings, where a single building is constructed with some street-facing rooms, but also with a number of rooms that face an internal open-air space. Individual homes can be designed to face a courtyard as well, and examples can be found at least as far back time as Pompeii before the eruption of Vesuvius. With perimeter blocks, the courtyard is shared between several different buildings. Blocks of row houses have a superficial similarity, but with that building type the internal space is clearly partitioned into private lots, with no common areas.
Note that I have not included lots in the following images. That is because ownership seems to vary within and between countries, and language barriers prevent me from easily pursuing the issue. However, what is important is the general form, and the agreement - whether through cultural norms or specific regulations - that the interior is not developed. (At least initially - over time the central courtyard is often filled in.)
Both the horizontal depth, or thickness, of the surrounding buildings, and their height, results from the regulations and practices followed in each country. In much of Europe, apartments have historically been constructed to 4 or 5 stories with a single staircase, which eliminates the need for interior corridors to separate the vertical circulation paths. That allows buildings to be as thin as 36'-40'. More typical in older areas is a thickness of 44'-48'. When multiple stairways and corridors are required, they are typically placed inside, pushing the dimension to 56'-60'. Higher figures are seen in luxury properties, where the rooms are much larger. If an exterior corridor is used, buildings can be very thin, but that arrangement is generally unpopular, and confined mostly to isolated towers.
In the image above, the block size depicted is again 260' by 580' buildable. Clockwise from the lower left, the building thicknesses are 40', 50', 60', and 70'. The height is 55', or 5 stories with a half-exposed basement and parapet. With the thinner buildings, the interior courtyard is quite large, and the distance between the interior apartments on the long sides is almost three times that of exterior apartments to blocks across the right-of-way. Occupants of interior apartments on the short sides would barely even notice the far end. The interior apartments on the long sides of the thickest building are still separated by twice the width of the street. Clearly blocks developed in the perimeter form could be reduced in size by a significant amount before the units are adversely impacted.
Here I have simply reduced the blocks to half their length. The courtyards are still larger than the street width, but the space is no longer sufficient to host an (American) football game. Nonetheless, it would still be possible to put a playground, a basketball or tennis court, and a gazebo for picnics within the space - if residents desired such amenities. These would be shared between fewer units, increasing the cost per unit, but would have less demand for usage. A clear advantage with smaller blocks is that the streets become more walkable, with more paths between destinations and more street frontage for businesses. The effect is greater with shorter blocks (blocks that tend towards being square) than narrower blocks (blocks that tend towards being long and thin).
There are some technical tradeoffs between the thicknesses. Thin buildings dictate that any spaces created for businesses on the ground floor would be relatively small. Many businesses feel they need certain dimensions to operate effectively, and avoid smaller units. Thick buildings provide larger floor plates, but also mean inside corners become difficult to allocate usefully on residential levels, increasing the price of each unit. Thick perimeters also mean that a large portion of each unit will receive little to no natural light, because the inner portions are used for kitchens, bathrooms, storage, and other support functions that are in small, closed rooms. At least some of those rooms have to be positioned on an exterior wall in thinner buildings, trading floor plan efficiency for natural light and fresh air.
The perimeter can be broken to resolve some of those problems, though at the price of the continuous perimeter, and an urban feel. And once the perimeter is broken, the desire for parking could overwhelm the desire for open space, and the interiors of the block could end up covered in pavement. Parking within the block would also reintroduce the problems associated with curb cuts. However, a less rigid adherence to building to the limits of the property lines in each block would allow for more architectural expression and a wider variety of living experiences.
| 24' RH, deep block | 40' Sixplex, 3BR units | Perimeter, 40' thick | Perimeter, 50' thick | Perimeter, 60' thick | |
|---|---|---|---|---|---|
| Gross length | 640 | 640 | 640 | 640 | 640 |
| Gross depth | 320 | 320 | 320 | 320 | 320 |
| ROW width | 60 | 60 | 60 | 60 | 60 |
| Net length | 580 | 580 | 580 | 580 | 580 |
| Net depth | 260 | 260 | 260 | 260 | 260 |
| Lot width | 24 | 58 | 580 | 580 | 580 |
| Lot depth | 120 | 120 | 130 | 130 | 130 |
| Lots per block | 48 | 20 | 2 | 2 | 2 |
| Parking – private (spots) | 2 | 5 | 0 | 0 | 0 |
| Parking – street (spots) | 0.6 | 1.5 | 0.11 | 0.07 | 0.09 |
| Driveway or alley (sq. ft.) | 240 | 580 | 0 | 0 | 0 |
| Pct. paved | 7.69% | 7.69% | 0.00% | 0.00% | 0.00% |
| Back yard (sq. ft.) | 1008 | 1508 | 42312 | 71744 | 59664 |
| Pct. back yard | 32.31% | 20.00% | 56.12% | 44.18% | 36.74% |
| ROW per unit (ft.) | 40.0 | 16.0 | 7.4 | 8.0 | 5.6 |
| Density per block (per/sq. mi.) | 26,136 | 65,340 | 89,843 | 103,455 | 133,403 |
I have used an assumption of two persons per large bedroom and one person per small bedroom to calculate densities, except for zero and one bedroom units, where I allocate one person regardless of size. The density values also reflect actual floor plans, which I have not shown here. The 40' thick buildings are laid out with 4 units per floor, with two facing out to the street, and two facing in towards the courtyard. This is similar to "garden" apartments found in America. The 50' thick buildings have only two units per floor, with exposures on both sides. This arrangement is common in Europe. The 60' buildings are fairly standard interior corridor buildings, with units ranging from 0 to 5 bedrooms. These are seen in many countries.
In general, I think that the blocks for this form of building could be reduced in size in one dimension or another from the 260' by 580' block I have been working with. However, the size remains effective, allowing for high densities. In an urban area with multiple different building forms, continuity with other parts of the grid is important. Without a pressing need to reduce the blocks, I will continue to work with the size I have been using. In a future post I will examine block sizes for high-density apartment buildings.
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