Street and Lot Layout

Street and Lot Layout

• by Peter Cotton

Street and lot layouts are important elements of the design of a residential area or neighbourhood.  This fact sheet sets out key considerations and influencing factors to inform designers to help them produce better designs of street and lot layout resulting in a more sustainable urban, environmental, social and economic outcome. 

The layout of streets provides the framework that connects the various elements of land use and the skeleton that supports residential lot layout.  As such, street and lot layout of a residential development are closely inter-related - one influencing the other.
The success of the design of a residential area must begin with the vision for the estate. Street and lot layout should not be treated in the traditional way of simply creating a land subdivision. There must be a clear nexus between house designs and lot creation: lots and lot layout should be designed with the end building typologies, uses and eventual built-forms in mind. Similarly, street layout, apart from providing the primary function of circulation and connectivity, should facilitate the creation of the desired lot layout to accommodate intended uses and built-forms, including residential, community, retail, commercial and educational. Also, street layout should provide the public space for positive, casual social encounters of resident pedestrians and cyclists.
Together, street and lot layout predicate and determine future arrangements of buildings and spaces, and the resultant quality of spaces, which, when considered in conjunction with unique site features, history and landscape, contributes to the character and identity of the neighbourhood.

Source: Development Code Precinct Planning , The Growth Centres

Outline

Street and Lot Layout Considerations	Influences
Objectives and Principles	Vision for Estate Sustainability - economic, social, environmental
Site characteristics	Existing unique site features - natural/manmade Local identity Surrounding development - existing/ proposed
Orientation	Solar access and energy efficiency Views and outlooks Proximity/ adjacency to open space Alignment of dominant site features to be retained Site configuration - predominant site aspect ratio
Street block sizes and dimensions	Permeability Distances between intersections - speed control
Street Pattern/network	Connectivity Walkability
Lot types	Access from fronting street available? Special requirements Noise attenuation required?
Lot sizes, dimensions and configurations	slope, orientation, existing site features, trees, views, setbacks, bushfire risk Market demand, demographics, socio-economics
Lot Mix	Market demand, demographics
Distribution of lot types/ densities	Locations of neighbourhood parks/ public open space, activity centres Public transport routes
Safety and security	Passive surveillance opportunities with lots fronting streets and open space

Objectives for Site

The success of the design of a residential area must begin with the objectives and vision for the site. It is acknowledged that different stakeholders will have objectives and vision that may or may not be aligned, if not outright competing and contradictory. For the purpose of this fact sheet, it is assumed that all parties have arrived at common objectives and vision for the site and that the design of street and lot layout can proceed with the agreed-to overarching objectives and vision in mind.
Clearly, the objectives and vision will vary from site to site depending on whether the development is an infill, a greenfield or brownfield; whether it is in an affluent, middle or low income area; and whether it is big enough to create distinct neighbourhoods, have its own neighbourhood activity centre, local centre, town centre, schools, employment centre, public transport systems etc.
Once the objectives and vision are established, it is then possible to apply principles and considerations to arrive at street and lot layouts that suit the site.

Site Characteristics

The first step in the design of street and lot layout for a development is to perform a detailed site analysis to determine the uniqueness of the site and its relationship to the surrounding area. Site characteristics such as slope and topography, natural drainage lines, existing significant trees, view corridors, erosion, rock outcrops, bush fire risks, noise source, odour source, cultural features (European and Aboriginal) all have influences on the form and pattern of street and lot layout and lot sizes. The resulting layout should be one that uses these site features to impart local character and identity to the development . It should strike a balance between the need to accommodate them all and other considerations such as economic, practicality, yields, desired urban outcome and other factors that may become evident in the course of the design process.

Source: Development Code Precinct Planning
The Growth Centres Commission

Orientation

There are a number of factors that drive the orientation of streets, and by association, lots that front the streets, the primary one being solar access to buildings and private open space to provide amenity, thermal comfort and energy efficiency. Other factors are: views and outlooks, proximity to open space, alignment of dominant site features to be retained, site configuration – in particular, predominant site aspect ratio and alignment of dominant site boundaries. In these cases, streets will need to be oriented to take advantage of view opportunities, enable lots to front open spaces, and be aligned with dominant site features and site boundaries, which may or may not be optimal in terms of solar access. It must be pointed out that these factors are site specific, whereas solar access is universal for all sites and the same principles can be applied for all sites, albeit mediated and tempered by specific site features.
Diagram of how lot layout affects dwelling orientation and solar access to the dwelling and garden in a temperate climate.
Source: Liveable Neighbourhoods, Western Australian Planning Commission

Street Block Size and Dimensions

One important element of street and lot layout is the size and dimensions of street blocks. Street blocks determine the permeability of a neighbourhood. The longer the street blocks, the less permeable the neighbourhood becomes, and vice versa.

High permeability resulting from reduced street block lengths increases connectivity and enhances the walkability of a neighbourhood, thereby encouraging less use of private vehicles. High permeability also means increased frequencies of street intersections, which in turn, discourages speeding due to increased frictions at intersections.

Another side benefit of reduced street blocks is the potential for improved streetscapes due to reduction in the relentless monotony of long street blocks with increased frequencies of lots turning the corner, and increased physical and visual breaks at intersections.

In terms of dimensions, the maximum length of a residential street block that offers good permeability is in the order of 200-220 m. (Ref..). The width of street blocks, on the other hand, is less critical and depends on the targeted lot sizes and depths, with the maximum cited by various authoritative sources to be in the order of 70m. (Ref…). This makes a typical perimeter block with maximum dimensions of 200-200m long x 70m wide.

Street Pattern/ Network

The pattern of streets affects traffic circulation and sets the framework for lot layout. The current preferred practice for street pattern is an interconnected network as against the conventional hierarchical and dendritic pattern where cul-de-sacs predominate at the lower scale. This has the effect of dispersing traffic by providing increased choice of pedestrian, cycle and vehicular routes to destinations; unlike conventional rigidly hierarchical structure of streets where residents living in higher order streets experience inequitable shares of traffic impacts - noise, fume, traffic concentration and safety.

Where normal network pattern cannot be achieved due to factors such as hilly terrains and steeply contoured topography, the network can be modified to accommodate the topographical variations, while maintaining the interconnectedness to facilitate traffic filtering and dispersion and consequent
more equitable sharing of traffic impacts.

Lot Types

There are a number of lot types to suit different locations and access conditions, or special conditions to handle issues such as noise, incompatible adjoining land uses and/or visual blight. The most common lot type is the one where lots make up “perimeter blocks” with direct access from the fronting street.
The next type is the one pertaining to narrow fronted lots that have a rear lane access for garages. If the lots are wide enough, it is possible to have garage access from the front as well as from the rear, albeit the front access will need to be limited to a single car width to minimise garage dominance of the streetscape. There are variations to the rear lane access arrangement that take on the form of mews or car-courts.

Then we have battle-axe lots that are used when the lots front access-denied streets or public open space. In the case where the development is a built-out, not a land sale, the buildings may be designed together sharing a common drive to garages and avoid facing the street to enhance the streetscapes.

Other types of lots are specially designed to block out traffic noise, turn their back on visual blight or undesirable/ incompatible development. These types of blocks require special house designs to take advantage of the special lot designs to be effective.

Images source: DCP 2006, Camden Council

Lot sizes, dimensions and configurations

Lot sizes and dimensions determine what housing types can be put on them. Typically, lots of 450 m² (15m x 30m) and over are suitable for most types of standard detached single dwellings.
For lots smaller than 450 m² and greater than 350 m² the range of suitable types of dwellings is reduced, tending towards L-shaped or courtyard plans, depending on orientation. For these lots, in order to gain efficiency and increased amenity in terms of increased visual and acoustic privacy and increased useable private open space, zero-lot-lining on one side should be allowed.
Lots smaller than 350 m², depending on their widths, may accommodate L-shaped or courtyard style houses, semi-detached houses, townhouses or terrace houses. The entire super-lot needs to be considered together to achieve optimal solar access, acoustic and visual privacy, and attractive streetscapes.
The effect of solar orientation on lot sizes and dimensions is already covered in Fact Sheet: Solar Access/ Lot Orientation. The reader should refer to this Fact Sheet for more information.

Source: Practice notes AMCORD
In the lot layout where particular types of houses are intended for particular precincts or neighbourhoods forming part of the overall concept of the masterplan, allowance must be made to the lot sizes to accommodate specific site features such as slope, significant trees to be retained, view sharing, setbacks requirements, setback from bushfire sources etc. The above may result in increased sizes for each lot types either in width, depth or the combination of both.
In terms of shapes and configurations, ideally lots should be of regular shapes, whether they are rectilinear or regular shapes following curvilinear streets. This is particularly so for lots smaller than 500 m² where the shape of the lot becomes more critical, as the proportion of a building increases with reduction in lot area, necessitating special building designs if the lot shapes are irregular.

Lot Mix

Ideally, a development should contain a range of lots designed for different types of housing to accommodate the varying housing needs of differing households, age groups and income levels of the future residents to make for a balanced social mix and vibrant community. There is no common guide as to what this mix should be in terms of the proportion of housing types. This mix will in practice be determined by market demands and locations. The key is to build in sufficient flexibility and robustness in the masterplan to be able to adapt to eventual demands without affecting the integrity of the overall concept and vision for the estate.

Subdivision layouts of street blocks must provide the lot yield or target density that satisfies the minimum density set in a district, regional or local structure plan. Diversity is achieved by varying lots sizes through the detailed area plan process (eg 20 dwellings per site hectare with DAP required in particular circumstances).

Source: Liveable Neighbourhoods, Western Australian Planning Commission

Distribution of lot types/ densities

Generally, lot distribution follows the transect of densities with smaller lots i.e. higher density, concentrated around activity centres and neighbourhood parks, with increasing lot sizes, i.e. decreasing densities the further away they are from activity centres and neighbourhood parks. 
In principle, medium density lots should be placed in locations of high amenity which may or may not coincide with activity centres or neighbourhood parks, such as open space corridors, nature reserves, lake/ water side, and so on. They should also be located along and within close proximity to public transport routes to maximize usage.
For presentation purposes, larger lots may be located near entries to the estate to create a relaxed, uncluttered and welcoming ambience to the estate and set the tone for the development.

Safety and security

The design of street and lot layout must optimise passive surveillance opportunities by ensuring lots directly address streets and open space. Lots with no direct street address are to be avoided as much as possible.

Where lots are provided with a rear lane access, passive surveillance of the lane is to be facilitated by requiring portions of the rear fences to be semi transparent and studios above garages located at strategic locations be required as part of the development consent. Laneways must also be arranged in such ways as to allow maximum passive surveillance opportunities form the studios.
Image Source : North Penrith Urban Area DCP Penrith City Council

Key Issues

Benefits

Giving proper considerations to a comprehensive range of factors affecting street and lot layout ensures that the desired results in terms of eventual urban, physical, economic, social and environmental outcomes are achieved for all stakeholders, be they the end users, authorities, service providers, developers, investors and the public at large. Each and every consideration themselves brings added benefits in their own areas as discussed in each of the previous relevant headings. Together, the synergistic effect of compounded benefits would make a development more than just mere land subdivisions, but one with a true sense of place, a esigned anned well thought out  much more desirable outcome overall.eration with consequent savings in power bills.f solar enersense of belonging with its own unique character, where the residents can enjoy all the amenities, convenience, comfort and safety of a well designed estate that facilitates social interactions, encourages walking and cycling, and promotes an active life style that would raise the general health and fitness of the community as a whole.

Risks

There are a number of risks associated with trying to accommodate all considerations to the maximum to achieve the best outcome for a particular site. For instance, the costs associated with retention of heritage items, preservation and enhancement of environmentally sensitive areas, preservation of existing significant vegetation etc. in terms of loss of yields or extra costs of services diversion may render the project financially unviable and abandoned altogether.

Another common risk is not having assessed the topography of the site sufficiently to highlight the need for significant amount of retaining walls and the unsuitability of particular housing types on steeply sloping land, resulting in extra building costs and untended built-form outcomes in designated precincts.

Blindly imposing a rectilinear grid pattern of streets and lot layout on steeply sloping sites is another risk that will result in incongruous development of questionable validity.

Other risks include incorrect identification of the market demands for products such as lot types, sizes, and targeted prices resulting in projects not selling as well as expected, impacting on the feasibility of the project resulting in cost cutting measures, which  invariably involves cutting budgets for landscaping and urban design features leading to less desirable public domain outcomes.

Changing demographics and migration trends also affect market demands, as indeed, do changing trends in housing tastes and space requirements, changing economic climates, movements in interest rates, and other unforeseen factors. The masterplan layout must be flexible enough to be able to accommodate changes in demands while maintaining the integrity of the overall concept and vision.

Savings

Site responsive design of street and lot layout taking into account natural topography and drainage lines would minimise cut and fill and engineered solutions to stormwater drainage resulting in savings in infrastructure costs.

Higher permeability, improved connectivity, walkability, pedestrian and cyclist accessibility to centres of activities and open spaces would encourage less use of private vehicles with consequent savings in fuel, reduction in emission, fumes, leading to improved air quality, reduced traffic noise, reduced potential for accidents, reduced operating and repair/ maintenance costs of vehicles.

 Walking and cycling and use of open spaces would lead to more active life styles with positive benefits to health and fitness of the community. Better health of the community means less expenditure on medications and health care services.

Street and lot layout that optimise solar access and facilitate passive solar design would reduce energy consumption for heating and cooling of dwellings, and maximise opportunities for collection of solar energy for electricity generation with consequent savings in power bills.

Costs

Achieving the desired outcome by giving due considerations to all major factors and influences does come at a cost in some areas. For instance, retaining unique site features such as significant trees, accommodating curtilages for heritage items and artefacts – both European and Aboriginal, preserving the natural ecology of a place etc. may involve a loss of development yields or incurring extra costs of diverting and increasing the lengths and/ or complexity of roads and services.

Similarly, trying to achieve high permeability by reducing block lengths in a network pattern instead of using loop roads and cul-de-sacs means more roads, hence, increased costs - although the typical roads in a compact neighbourhood model are narrower than the standard roads of a standard subdivision, so the extra costs may not be proportionately significant. Also, more roads means some loss in yields, hence loss of development revenue.

Other costs directly attributable to street and lot layouts, in particular, those relating to orientation are the additional building costs of trying to achieve solar access to the main living (family room) area of a dwelling on a north-oriented lot which necessitates a C-shaped courtyard plan form with a single storey portion fronting the street to allow the sun into the central courtyard and family room in the back, if east-west street orientation cannot be avoided due to other more dominant factors.

Still related to costs due to orientation is when the desired orientation works against the slope of the land requiring retaining walls, which add to extra costs of construction.
In spite of the extra costs in many areas, the benefits of a more site responsive, environmentally, culturally and socially more sensitive design of a development far outweigh the costs and produce a much more desirable outcome overall.

Barriers

Although at policy level, local councils have expressed support for New Urbanism-inspired street and lot layout which is basically a grid pattern with resultant cross-intersections, in practice, however,  barriers to implementing this model have been encountered with conservative council engineers who are more focused on making streets as safe and efficient conveyors of vehicular traffic as possible at the expense of pedestrians and cyclists. The main barrier in this regard is the engineers’ aversion to cross-intersections and their preference for T-intersections. Whenever there is a cross intersection they would want to install a round-about, which has a negative impact on the amenity of residents of dwellings at the intersections and adds further frictions to the flow of pedestrians and cyclists. T-intersections also do not allow view corridors or direct visual connections, which cross-intersections do. Dwellings at the end of the T-intersection are also affected by beams of headlights at night.

Another barrier to implementing compact neighbourhood concept involves road standards. For various technical and engineering reasons, council engineers are generally resistant to reduction in road widths, which makes implementing New Urbanism- inspired more pedestrian friendly road designs in a new estate an uphill battle.

Issues of maintenance costs and liabilities to councils are also common barriers to introducing innovations to estate designs, including street layout designs. There have been instances where proposals with site responsive street layouts designed to incorporate innovative water sensitive urban design features into the medians and verges, but got knocked back because of perceived additional maintenance costs and liabilities to councils. This restriction applies to water features and small pocket parks under a certain size, which would have added amenity and visual relief as well as enhanced the landscape quality of an estate, but are not allowed by council.

Benchmarks

There are no known tools for measuring the overall performance of the design of street and lot layout or the performance of the whole estate. Most tools that are available deal with ratings of environmental performances of individual buildings. The tools that come closest to establishing any kind of benchmarks in the area of urban planning and design are:

• The Seda Solar Access for Lots (SAL), Guidelines for Residential Subdivision in NSW.
• SPeAR - Sustainable Project Appraisal Routines  - based on a qualitative approach - not performance based.
• Dockland ESD Guidelines - a pattern book approach - not really performance based.

Ultimately, benchmarking to measure the success of an estate design should go beyond measuring against physical, functional and environmental indicators. It should extend to cover the well-being of the community for which the estate has been designed to serve. There has been a benchmarking project initiated by the Local Government Community Services Association of Australia looking into establishing indicators to measure the well-being of a community based on theme areas such as:

• Economic Vitality
• Celebration of Place
• Ease of Access to Services and Facilities
• Community Harmony
• A Healthy Community
• Participation in Community Life
• A Safer Community
• Cultural Development.

Development phase actions

Feasibility

Two aspects of feasibility will be explored here: financial and physical.

In terms of financial, a yield analysis based on a preliminary land-take and an average density across the site, taking into account known constraints and existing site conditions,  should reveal if the project is worthy of further investigation.

A study of similar projects, firmed up by market research on demand and supply of residential lots in the area would produce a brief for targeted lot sizes and mix of housing types, as well as the price levels expected for the market. This is quite a critical step as it forms the basis for the whole financial feasibility for the project.

Still on financial feasibility: an area frequently missed when undertaking feasibility analyses of a project is failure to account for the topography of the site in the costing where steep slopes necessitate significant retaining and earthwork. This would have a drastic impact on the financial feasibility of the project.

On the physical side, the feasibility for adopting a particular approach such as a grid pattern of street network may need to be assessed against the topography of the site. A steeply sloping site, for instance, may render this approach impracticable.

Similarly, the objective of maximizing solar access by orientating lots within the optimum range may not be feasible due to other constraints such as south-facing steep slopes, alignment of dominant site features to be retained, site configuration -in particular, predominant site aspect ratio and alignment of dominant site boundaries.

Planning

Planing of the street and lot layout begins with the detailed analysis of the site constraints and opportunities: its unique features - natural and man-made, physical, cultural and historical, its relationship and connection to the surrounding context. Also important is how it fits in with existing government urban strategies, planning policies - existing or proposed controls.

From the analysis of the above, patterns will begin to emerge, informed by the various factors considered, showing the likely structure, locations and inter-relationship between land-use elements such as nature reserve/ environmentally/ culturally sensitive areas, public open space, mixed-use activity centres, employment and residential areas, each connected via a network of movement corridors and circulation system, and linked to and integrated with surrounding areas (if desirable).

Depending on the scale of the development and the size of the site, a number of distinct neighbourhoods of 400m radius centred around neighbourhood parks or activity centres may begin to form and fill out the masterplan.

More detailed analysis will identify locations suitable for different mix of residential densities generated by different lot types and sizes.

Once the structure plan is all firmed up and agreed to by all stakeholders, more detailed design of the street and lot layout can take place to give substance to the concept.

Design

Crucial to the realization of the vision for the estate is the “design” of the street and lot layout. Design involves refined skills combining functional understanding and aesthetic flair. No given amount of policy statements or planning controls can guarantee good designs.

Street Layout:
When designing a street layout, it is important to be aware that streets are not mere dividing lines or means of conveying vehicular traffic. Streets are also communal rooms and passages for pedestrians and cyclists. Choosing an appropriate street pattern suitable for the site and topography to achieve connectedness and continuity of movement is the starting point in the design of street layout. Inter-connectedness does not, however, necessarily mean being gridded in a rectilinear form. Curvilinear shapes on plan and figures that respond to the topography and site features can add interest and variety to the pattern, while still achieving good inter-connectivity.

Closely allied to the choice of pattern is the orientation of streets. Ideally streets should be designed to be oriented to maximise solar access to lots and buildings. There may be other more compelling factors that determine the predominant orientation of streets such as: slope and topography, alignment of dominant site features to be retained, alignment to capture significant views, predominant site aspect ratio and alignment of dominant site boundaries.

Assigning appropriate hierarchy to streets to reflect the function and expected traffic volumes is the next step. This will generate streets of different widths and sections, which are differentiated in terms of the number of carriageways, parking provision on or off-road, whether there is a cycle lane – on road or off-road and whether this is a footpath, if so is it on both sides, or just one side of the street.

In general, streets should be as narrow as possible to slow down traffic and make them more pedestrian friendly. Kerb radii should be kept to a minimum to facilitate pedestrian crossings at intersections and slow down traffic. For wide higher level streets, landscaped medians incorporating water sensitive urban design should be provided to reduce the apparent street widths.

Another aspect of street layout is determining the spacing of street intersections. This affects the permeability of the neighbourhood and the walkability of streets. Spacing of intersections is closely related to the size of street blocks – the shorter the blocks, the more permeable the neighbourhood and consequently, the more walkable the streets.

Lot Layout:
The design of lot layout starts with the street blocks that follow the street layout, which provide the framework for more detailed design. At this stage locations of various residential densities have already been determined, as are lot orientations which are the resultant of street orientations. It is a matter of laying out the lots to the mix already stipulated in the brief.

To avoid monotony, there should be a mix of lot sizes i.e. widths, in a given density in the same street block. Lots at the ends of blocks should be rotated to address cross streets to reduce the number of lots in a continuous row. In medium and higher density areas, especially lots designed for townhouses and terrace houses, the maximum number of lots in a row without a break need to be set.

The design of lot layout needs to go beyond just carving out land into lots. The designer must have the desired built-form outcomes in mind. Ultimately, it’s the built-forms that are the most legible part of a neighbourhood. As such, lots need to be laid out to facilitate the creation of built-forms that provide a sense of enclosure to communal open spaces, define the communal rooms afforded by streets, and celebrate places of special significance such as entries to the estate, gateways to neighbourhoods or precincts, lots framing important axes or view corridors, sites for landmark buildings etc.

Construction

By the time a project gets to construction stage, everything relating to the design of street and lot layout would have already been resolved and hopefully all the infrastructure and utility services would have already been coordinated and clashes ironed out. However, there may be occasional unlikely events whereby changes to the layout may need to be made during construction due to unforeseen obstacles such as discovery of important relics during excavations and earthworks, changes in the hydrology and flow pattern of creeks due to disturbances up or downstream causing the rising of flood lines etc.; not to mention changes occasioned by unexpected costs such as extra retaining and earthworks, to increase yields by changing lot sizes to maintain the financial feasibility of the projects. Fortunately, these are rare exceptions that cannot be factored in when undertaking the planning and design of a project.

Lot Creation

Depending on the size of the land, generally lot creation occurs on a staged basis whereby lots are released onto the market based on the projected sales rates driven by market demands. The task here is to work out a staging strategy that includes a representative mix of lot types and sizes in each stage while ensuring the completeness of each stage in terms of servicing, presentation, communal facilities etc. ensuring that staging progresses in the way that facilitates construction sequences without impacting on the amenity of residents in completed stages.

It is common practice to create lots as land sales to end buyers and super-lots for medium density areas where houses have to be designed and built as an integrated development following the indicative lot layout on the masterplan by the developer, or packaged out to other builders/ developers.

The developer may also elect to build on selected lots in key locations to set the tone and standard for the estate; in which case, special lots may be created to showcase their premium products.

Completion

In reality, not everything will turn out as planned or designed for – some will work well; others may fall short of expectations. It is good practice to carry out a post-completion review of the project to list the good, the bad and lessons to be learned to be applied to future projects.

Items for review may include:

• Functioning of streets in terms of traffic flow, parking, utility services, service vehicle movements etc.
• Spatial and landscape quality of streets as “communal rooms” – street trees, verge planting, medians landscaping/ WSUDS
• Effectiveness of lot layout in terms of desired built-form outcomes, intended house types, streetscapes,  private open space, acoustic and visual privacy, solar access, energy efficiency, site costs
• Overall neighbourhood character, sense of place, sense of identity, community harmony, ease of access to facilities, evidence of active life style through frequent patronage of parks and open space, walking and cycling, evidence of perception of safety and security