Urban Rules and Water by Claudiu Forgaci

Sterrenburg, Dordrecht

Technology Assignment Urban Rules and Water Claudiu Forgaci European postgraduate Masters in Urbanism 19 April 2012

Sterrenburg

Sterrenburg is a district of Dordrecht, located on the Southern edge of the cityâ&#x20AC;&#x2122;s urbanized area. Most part of it was built in the sixties and seventies, thus clearly showing the characteristics of that periodâ&#x20AC;&#x2122;s trends in housing development. Because of its large surface, it is divided and numbered in three chronologically successive sections: Sterrenburg I, II and III. The current study will focus on the second and third section, located Soth to the Zuidendijk. There is a clear contrast between the housing typologies of northern and the southern sides. Sterrenburg I and II are mainly occupied by high-rise buildings with flats, while Sterrenburg III is mainly a low-rise area with singlefamily, attached or row housing. Programatically, it might be characterised as a monofunctional development, seeing that additional local services (education, commercial activities etc.) ar kept to a minimum and only serve the area of the nighborhood.

Dimensions and density figures: Study area: Built footprint:

2,4 sqkm 0.4 sqkm

Low-rise area: High rise area:

2-3 floors 10 floors

FSI: 0.66 GSI: 0.18 OSR: 1.25 L: 5 (average between 25% 10 floors and 75% 3-4 floors) N: 0.02

I II III

Sterrenburg, Dordrecht

High-rise ar

Sterrenburg I

Ster

rea

rrenburg III

Agrregation level: District

Study area 2,4 sqkm

Road network 331963sqm

Surface water 111743 sqm

Built footprint 0,4sqkm

Builtup areas 1,4 sqkm

Tare space - parks 0,5sqkm

100m

500m

1km

main roads

waterways

dikes

Fixed elements

Existing rules

The following set of rules represents a minimum set of conditions considered to be sufficient to design a similar neighborhood. They were intuitively extracted from the present layout of the neighborhood, rather then being taken from a masterplan or urban regulations. Typical to the period when it was constructed, Sterrenburg clearly resembles the positive and negative characteristics of that period. Briefly, these rules lead to a very green (see Water, The Green Sandwich), remote neighborhood (see The Loop), with a large proportion of isolated low-rise housing (see Parking Facilities, No blocks, The Tree) and a smaller segregated collective housing area (see Social Order), with the tipical suburban image of a dormitory neighborhood (see Sloped Roofs).

Parking facilities

The tree

Social order

Public parking facilities should be positioned at a maximum distance of 200m from the main road. Exceptions are the high density collective housing areas, where 20% of the buildingsâ&#x20AC;&#x2122; enclosed parking lots must be provided for the public.

The main access loop must branch out into a clear hierarchy of secondary and tertiary roads. Based on this structure, secondary roads serve as access roads for sub-areas with no more than 200 dwelling units and tertiary roads are considered dead-end streets serving no more than 20 dwelling units.

The neighborhood must be clearly divided into two different types of housing areas: (1) collective and (2) semi-collective/individual housing. (see full description of the rule below).

1 200m

<10 floors

2 3 3 3

20%

<3 floors

Water

The loop

The green sandwich

The existing creeks must be preserved, integrated as public water features and regulated with a canal enclosing the perimeter of the site. In order to transform these creeks into public water features, at least one continuous side of each branch must be accessible to pedestrians and free of private properties on a distance of 10 meters from the waterside.

The neighborhood must be served by a primary access road loop with a diameter of 1km + 100m, optimal to connect the whole area of development. No more than two additional, therefore a total of 3 access roads should link this loop to the same neighboring road, with an average distance of 300-500m between them.

Every built component of the develpment should be separated from the neighboring component by trees. Built components considered here are: buildings, roads, playgrounds or sportsfields, canals and parking spaces. For these components the following conditions must be fulfilled: • for every 5m of building perimeter at least one tree will be planted, in a maximum distance of 10m from the building; • for every 5m length of canal or waterway at least one tree will be planted on its side, not farther than 5m from the water edge. • every playground or sports field will be bordered with trees, at a maximum distance of 5 meters between them; special attention will be paid to the visibility of the playgrounds - they still need to be visible from the outside; • each parking lot will have a tree assigned to it;

300500m

1km

* if the conditions described above overlap (e.g. parking lot next to bouilding), the assigned tree can be shared among all the components invoved. Private properties must leave 75% of the unbuilt surface of the plot unpaved and covered with vegetable soil. For every 50sqm of this surface one tree will be planted within the boundaries of the plot. For example: ((300sqm(plot) 120sqm(built))*75/100)/50sqm = 135sqm / 50sqm = 2.7 = 3 trees.

No blocks

Sloped roofs

In the low-rise area buildings will be organized in such a way that enclosed blocks can be avoided. For every built island (area delimited by roads), public access into the middle of the island must be provided.

In the low-rise area (see ‘Social order’), all buildings must have sloped roofs. All roofs will be sloped at a 450 angle.

New rules

The main issues of the neighborhood seem to be isolation, social segregation, monofunctionality and low sustainability. Therefore the rules dealing with these negative aspects are being replaced. Instead of designing for social segregation, Social Mix is being encouraged; in order to improve inner and outer infrustructural connections, the road structure is transformed into an interconnected network (see Network); rain water storage and garden roofs are encouraged (see Garden Roofs).

Parking facilities

Network

Social mix

The road structure must be an interconnected network, thus allowing connections not only with the outside but also between communities within the neighborhood. (see the full decription of the rule below)

The neighborhood must offer a balanced and evenly distributed mix of housing typologies. (see the full decription of the rule below)

200m

2-10 floors 20%

Water

The loop

The green sandwich

300500m

1km

No blocks

Garden roofs

New low rise housing buildings need to have at least 50% of their roof surface covered with a roof garden. The roof garden is defined here as a horizontal surface covering the building, which is composed of a layer of at least 30cm of vegetable soil. This way the maximum gross floor area may be increased with an additional surface equal with the surface of the garden roof.

50%

Social order The neighborhood must be clearly divided into two different types of housing areas: (1) collective and (2) semi-collective/ individual housing. The two areas will be organized as follows: (1) High-rise (collective housing) area: • It is accessible from the main road within a distance of max. 500m. • It contains 50% of the total number of dwelling units. • It occupies max. 25% of the neighborhood’s surface. • The height of the buildings may not exceed 10 floors. (2) Low-rise (semi-collective/individual housing) area: • Contains 50% of the total number of dwelling units. • The height of the buildings may not exceed 3 floors.*

Variety

8 floors 25% assigned land

* The attic may be used as an additional floor. (see Sloped roofs)

<10 floors

10 floors 15% assigned land

<3 floors 10 floors 15% assigned land Observations: • By spatially delimiting the two typologies, social segregation is encouraged. • The semi-collective/individual housing area risk to become exclusively semi-collective due to the possibility of having more dwelling units in that typology. A regulated proportion between the two subtypes is missing. • The number of dwelling units is not defined, therefore the proportions defined above can be applied to any number of dwellings that fit into height restricitons. Even if it is not probable, one of the two areas could have a very low number of dwellings, thus conditioning the other area to the same (low) amount of units (1:1 ratio). 12

Social mix The neighborhood must offer a balanced and evenly distributed mix of housing typologies. Therefore the following conditions will be assigned to them: (1) Collective housing: • It contains 30% of the total number of dwelling units. • The height of the buildings must not exceed 10 floors. (2) Semi-collective housing: • It contains 50% of the total number of dwell ing units. • The height of the buildings must not exceed 3 floors.* (3) Individual (detached, attached) housing: • It contains 20% of the total number of dwelling units. • The height of the buildings must not exceed 2 floors.*

Variety

compact/gradual development

* The attic may be used as an additional floor. (see Sloped roofs) Type (1) and (3) areas may not be positioned next to each other. There must be at least a type (2) parcel between a type (1) and type (3) parcel. scattered/gradual development

2-10 floors

scattered/gradual development Observations: • The compatibility between areas (1-2, 2-3) is applicable to all scales. It might ragulate large areas, but a small number of buildings as well. • The position of the areas is not restricted in any way, therefore a wide variety of arrangements are possible. • There is no restriction regarding the land surface occupied by a certain type. The mix is regulated by the number of dwellings.

Sloped roofs In the low-rise area (see ‘Social order’), all buildings must have sloped roofs. All roofs will be sloped at a 450 angle.

Variety

450

detached house 2 slopes parallel to the street

2 detached house 2 slopes perpendicular to the street

Observations: • A clear image cannot be defined just with these conditions. Still a great formal variety is possible by the combination of housing typologies, building orientation and the number of slopes. • The proportion between the slopes is not defined. Therefore, even if not probable, atypical roof geometries are still possible (see illustration 5) • According to the oservations on ‘Social order’, it is highly probale that semi-collective housing would dominate the neighborhood and replace detached/single-family housing. Following this logic and based on the feasability and efficiency of this kind of neighborhood, the predominant image of the buildings in this neighborhood would be the one illustrated at point 7.

3 detached house 4 slopes parallel to the street

4 detached house 4 slopes perpendicular to the street

5 detached house assymetrical slopes

row houses 2 slopes perpendicular to the street

row houses 2 slopes parallel to the street

Garden roofs New low rise housing buildings need to have at least 50% of their roof surface covered with a roof garden. The roof garden is defined here as a horizontal surface covering the building, which is composed of a layer of at least 30cm of vegetable soil. This way the maximum gross floor area may be increased with an additional surface equal with the surface of the garden roof.

50%

Variety

1 detached house 50% garden roof

2 detached house 50% garden roof

3 Observations: • By rewarding the building of a garden roof, private owners can be stimulated to make their roofs more sustainable (temperature regulation and water retention). • This rule creates an even larger variety of built geometries, therefore enhancing the architectural possibilities and qualities of the neighborhood. • In an extreme situation, due to the spatial advantages of the floor under the garden roof (compared to the attic in the case of a sloped roof), the neighborhood might totally transform its image into a neighborhood with terraced housing. However, the increased costs of a green roof should (normally) keep both typologies present in the neighborhood.

detached house 50% garden roof

4 detached house 50% garden roof

5 detached house 100% garden roof

row houses 50%-100% garden roofs variety

The tree

The loop

The neighborhood must be served by a primary access road loop with a diameter of 1km±+ 100m, optimal to connect the whole area of development. No more than two additional, therefore a total of 3 access roads should link this loop to the same neighboring road, with an average distance of 300-500m between them.

1 300500m

300500m

2 3 3 3

1km

Observations: • The two rules have a direct influence on the accessibility of the neighborhood. The access loop prevents passing-through traffic, but at the same time isolates the neighborhood from the rest of the city, thus decreasing the chance of development. The tree strengthens the isolation of the dwelling units, especially the ones situated on the last, dead-end branches. • The tree-like hierarchical structure of the streets also prevents social interaction among local inhabitants. This way it will not be compatible with the Social mix rule presented above (see ‘Social mix’).

Variety

end section of the tree structure cul-de-sac low-rise areas

end section of the tree structure cul-de-sac high-rise areas

The network The road structure must be an interconnected network, thus allowing connections not only with the outside but also between communities within the neighborhood. • The main road structure must connect to existing intersections on the edge of the of the neighborhood; • Inner secondary connections must be connected to at least 2 major road networks defined at the previous point. • Dead-ends are only allowed for accessing a maximum number of 4 parcels.

Variety

1 existing potential outer connections on the border of the site

2 main road structure based on outer connections

3 local interconnected network

Observations: • By integrating as many outer connections as possible, the neighborhood will be more integrated into the city. This way, passing-through traffic may be encouraged, thus increasing the importance of the area on the city level. • Secondary inner connections are meant to connect communities within the neighborhood. Accessiility is raised in all parts of the develpment, and so is the quality of living. • The tertiary roads defined here are meant to serve inaccessible areas. If they are kept in a small proportion in relation to the rest of the roads, extreme isolation is not a problem. • The structure defined this way is compatible with the ‘Social mix’ defined above. (see ‘Social mix’)

4 detached house 50% garden roof

• According to the chosen housing typologies, their position, topography, water network, outer connections etc., the network may take a wide variety of forms.

Spatial outcomes

schematic representation of the outcomes based on existing rules

Spatial outcomes These rules are samples of how the general design of the neighborhood might be guided, and only represent a part of a larger set of rules needed at this scale. Monofunctionality (mentioned as an issue at the beginning), is not addressed here. In this particular case, rules that are meant to improve funtional mixity would have to be added. However, by improving the integration of the neighborhood, achieving a proper social mix, functional mixity could be indirectly encouraged. As a result of introducing the rules above, the neighborhood has the following charcateristics: â&#x20AC;˘ diverse and mixed housing typologies encourage social interaction; â&#x20AC;˘ the integrated and interconnected road network supports development and encourages interaction between local communities; â&#x20AC;˘ it provides more sustainable solutions through incerased accessibility and greener architectural solutions.

schematic representation of the outcomes based on the new rules

Rules related to water

According to the calculations (see Table 1), the neighborhood has a large surplus of infiltration fields, therefore water coming from heavy rainfall is easily retained and evacuated. Water retention canals, ground and roof infiltration fields occupy a large surface of the development. Even though this might be seen an opportunity to create more hard surfaces, there is no need for it in the current (green) face of the neighborhood. However, the risk of flooding is still high, therefore existing and new buildings need to be regulated to deal with severe flood scenarios. Infrustructure, residential areas and public buildings of high importance need to be prepared by means of flood - proofing, land raising or by creating floating structures. Evacuation is also a vital component of flood-proof strategy: buildings need to be accessible, even during a high flood. (see ‘Water proofing’ )

Table 1 Water capacity Land cover type

Area (fabric)

Depression storage

Infiltration loss

Specific storage

Delay

[mm]

[mm/h]

capacity

[min]

Sterrenburg II, III

surface in m2

x 30 mm water in two hours = m3 water

Flat urban area; sandy topsoil Unpaved Surface water

111743.00

335.229

0.5 m3/m2

Rain garden, infiltration field

516220.00

15486.6

0.1 m3/m2

-63236.95

725788.5

21773.655

0.1 m3/m2

-51893.87775

Playground, footpath

0.1 m3/m2

Vegetated swales

0.5 m3/m2

Roofs – sloping

353569

10607.07

Roofs – flat, tar

59206

1776.18

0.05 m3/m2

1746.577

Green roofs – extensive

0.1 m3/m2

Green roofs – intensive

0.2 m3/m2

298766.7

8963.001

0.05 m3/m2

29876.67

896.3001

0.05 m3/m2

289.803699

Lawn, garden, green belt, shrub

Paved 10571.7131

Total footprint

Roads, car parks – asphalt Roads, car parks – porous asphalt Roads, car parks – brick Roads, car parks – porous pavers Sidewalk, terraces –tiles

Total Area

0.05 m3/m2

241929.5

7257.885

0.05 m3/m2

3314.43415

2337099.37

67095.9201

Other data built floor area

1534355

length of streets

Spacemate FSI

8933.12433

0.66

-90275.17547

Water

Water proofing

The green sandwich

According to the flood scenarios, the following measures will be taken:

Every built component of the develpment should be separated from the neighboring component by trees. Built components considered here are: buildings, roads, playgrounds or sportsfields, canals and parking spaces. For these components the following conditions must be fulfilled: • for every 5m of building perimeter at least one tree will be planted, in a maximum distance of 10m from the building; for every 5m length of canal or waterway • at least one tree will be planted on its side, not farther than 5m from the water edge. • every playground or sports field will be bordered with trees, at a maximum distance of 5 meters between them; special attention will be paid to the visibility of the playgrounds - they still need to be visible from the outside; • each parking lot will have a tree assigned to it;

(1) Flood in a closed system - 1m: • Every existing building must be adapted to the following waterproofing standards: ground floor utilities, including mechanical, electrical and plumbing must be adapted to flooding; bedrooms must be on the upper levels; ground floor openings must be water resistant. (2) Flood in an open system - 2.5m: • New buildings within the dike-ring will be designed as amphibious structures. • Buildings along the dike- ring will act as protective structures. Their first floor will be made floodproof and raised to the level of the dike-ring. Living functions are not allowed on this first floor. Parking and small commercial activities may occupy this floor. • Hospitals, schools, fire-stations, crowded public areas and other buildings of high importance will be raised on mounds, at the same level of safety as the dike-ring. • The main road structure (see ‘The network’) must be raised to the same height as the main dike ring; where not possible, secondary roads will have floating structures embedded in the walkways, so that evacuation is possible. • Dikes must be raised 1m above the expected 2.5m flood.

50%

Scenario 1 next to a river with frequent flooding

Scenario 2 heavy rainfall