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Ben Guy, November
2001
URBAN BLOCKS
WHAT ARE BLOCKS AND WHY SHOULD WE THINK ABOUT THEM?
Blocks are a, if not the, fundamental
element of urban form. Blocks are defined as 'an area of land
completely surrounded by public routes'. They define the edge
of the private realm and the beginning of the public. The
block edge is that nebulous realm where private and public
spaces intermingle. This intermingling may be to the mutual
benefit or detriment of both private and public arena. Even
when we do not plan for, or with, blocks - they cannot be
avoided. It is best, therefore, to harness their power to
our benefit. Only dispersed agricultural buildings or linear
towns/villages that are one-plot wide are relatively 'block-less'.
Blocks are all-pervasive in the (sub)urban context, yet mostly
ignored in local planning.
Blocks are the most resilient morphological
element of the urban milieu. Once a block framework is established,
consciously or not, it will last for millennia. The plots
within the block may change through subdivision and amalgamation.
The buildings within the plots may change through decay, demolition
and reconstruction. The materials, colours and building elements
may change through user alteration with a 'lick of paint'.
The block structure will remain. Another way to see it is
that streets, which are the gaps in between block edges, change
very rarely. Only with large-scale redevelopment are blocks
reconfigured. This was common in 20th century Modernist-inspired
'comprehensive redevelopment', primarily in inner urban areas.
The result of such development was usually to reduce the number
of blocks and streets and increase the size of blocks, as
well as plots. Even when this occurs, the initial block structure
can still usually be discerned. Jacobs 1993 provides an extreme
example in Boston (sees below).
It is indeed difficult to identify any continuity
in the Boston downtown area, which was once called 'the most
European of American cities' in the sense of walkability,
enclosure and intimate vitality (but now is not). In a study
of part of Norwich, about 1.5hours north-east of London, I
have traced the block morphology over nearly two millennia.
After the first Roman roads were established, which the Saxons
didn't change too much, it is clear that the basic block outline
is relatively stable up until 1970. The major changes occurred
when the Normans, for reasons best known to themselves, built
their majestic cathedral right in the middle of one of the
original roads. The second major change occurred with the
comprehensive development, 'slum' clearance and ring road
insertion in the late 1970's. Magdalen Street was, at the
end of the 19th century, one of Norwich's "liveliest
shopping streets". The 1995 Local Plan (ie Planning Scheme)
designated it the equivalent of a 'regeneration area'. It
is a mess. The carving up of the urban landscape took no notice
of the characteristics of the vernacular blocks nor their
re-expression with the new transport artery. The backs of
buildings are facing public spaces, there are large indecipherable
'gaps' along the streetscape, new road widths (ie gaps between
blocks) are uncomfortable in their excessiveness, and so on.
The rational planning and design direction is to incrementally
re-assert the vernacular block, as well as plot and perhaps
building, typologies. The street (via the people) will regenerate
itself simply through its consistent expression of local physical
character.
So what are the desirable characteristics
of blocks? The first fundamental issue is the perimeter block.
The public arena should be lined with the doors and windows
of buildings. Private fronts are on the edge of the block,
and private backs in the centre (ie back-to-back plots). There
should be no blank walls or open yards to the street. This
applies equally to streets, rivers, parks, train lines as
well as industrial, commercial, residential and urban areas.
This is to be expressed in all occasions, without exception.
The recently invented CABE (Commission for Architecture and
the Built Environment) in the UK, an advisory body to the
government, state that ignoring the perimeter block is their
most repeated objection to development proposals. The perimeter
block makes sense in terms of producing an 'animated' or lively
public scene (espoused by Jane Jacobs since he 1960s). It
also makes sense for security: the street is effectively 'walled
in' by the façades of buildings, so there are few possibilities
for dubious entrance. When a rear/side garden is along a street
- it is too easy to jump the fence and cause mischief.
What about block sizes? The modern residential
plot is some 25-35m deep. Plot frontage should be wide enough
to allow for air circulation and the penetration of sunlight
or cooling effects of shade to minimise electricity consumption.
Therefore, a block, being two plots wide, should be 50-70m
deep. Hayward (1993) discusses the 'ten-metre sausage' (ie
the building envelope) in the residential context producing
typical plot depths of 40-55m. These block sizes are typical
in contemporary UK residential development (Hall 2000). In
the urban scene, it has been argued that the 90m wide block
is a most robust form to suit most purposes (Bentley et al
1985). However, block sizes should be minimised to increase
permeability - the number of movement options throughout the
built environment. Good permeability also means good connectivity
of streets and lanes. That is, the perimeter block inherently
votes against excessive use of the cul-de-sac. Historic urban
forms have small perimeter blocks, and therefore high permeability,
with narrow gaps (ie streets) between the blocks (usually
3-15metres). These are the forms to which we flock, as tourists,
today. Small perimeter blocks are what we like.
So - think about your blocks in both existing
and proposed greenfield development. How can more blocks be
created? How can I generate connectivity? Do all the buildings
face the edge of the block? What is the historic block character
of this area? Map the local blocks over several decades and
centuries. Before even worrying about land-use or building
types, sketch out the basic block structure for a parcel of
land - you will find it almost designs itself once you know
the required plot depths and the perimeter block concept.
Developers may argue against more roads, to create defined
block edges, as they are expensive. Barter by proposing they
provide narrower streets with set-forward buildings to create
space definition without those silly, and expensive to maintain,
grassy 'nature strips'. In urban areas, accept no compromise
other than the smallest perimeter blocks possible. Superstore
developers are our greatest challenge.
Ayers, Brian (1994). Norwich. English Heritage.
B.T. Batsford. London.
Bentley, I., Alcock, A., Murrain, P., McGlynn, S. and Smith,
G. (1985). Responsive Environments: A Manual for Designers.
London, Architectural Press.
Hall, A. C. (2000). A New Paradigm for Local Development Plans.
Urban Design International, 5, 123-140. Stockton Press.
Hayward, R. (1993). Talking Tissues. Hayward, R. and McGlynn,
S. (eds) Making Better Places - Urban Design Now. Butterworth-Heinemann,
Oxford.
Jacobs, Allan B. (1993). Great Streets. MIT Press. Cambridge,
Massachusetts.
Jacobs, Jane. (1961). The Death and Life of Great American
Cities. Random House.
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