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A subdivision design needs to maximise and protect solar access for each dwelling. Thus, consideration needs to be given to the fundamental basics – orientation, shape, size and width of the lot, solar setbacks and building heights.

Effective solar access actually also incorporates solar protection. Passive designed homes need to be able to harness the warmth of the sun during the winter months, but be protected from the hot summer sun. Good lot orientation coupled with good passive design principles will allow a dwelling to achieve both these aims.

Although solar access and protection is often related to temperate climates, tropical areas also benefit from good lot orientation. In tropical areas, solar protection is the key driver and it is essential to ensure that windows can be shaded. The picture above shows a passive designed home in tropical Rockhampton. Note that the windows are perfectly shaded by the eaves. This can only be achieved through good design and orientation.

Design principles

To maximise solar access the design of subdivisions should be based on the following principles:

Source: AMCORD, 1995

Street Layout

• Align streets east-west and north-south wherever possible
• Aim for north-south streets within 20° west and 30° east of true north
• Aim for east-west streets within 30° south and 20° north of true east

Land uses and densities

• Concentrate the highest densities on sites with the greatest potential for good solar access.
• Locate larger lots where solar access is poor.

Source: AMCORD, 1995

Lot layout and orientation

• Where streets are within the acceptable orientation range, use rectangular lots
• Locate as many long lot boundaries as possible within the permissible orientation range
• Where the street is not within the orientation range, consider skewed lots, that is, lots with side boundaries that are not perpendicular to the street.
• Undertake a Solar Access for Lots (SAL) study to determine the relevant solar access zones
• Locate the narrowest lots on the north side of east-west streets
• Lots on the south side of the east-west streets need to be wider
• East-west lots need to be wider unless two storey construction is to be restricted
• East-west lots can be narrower if there is road or open space to the north (e.g. a corner lot)

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Orientation

Good orientation of lots within a development will enable well orientated homes to be more easily achieved. North-facing slopes improve opportunities for solar access; small lots are best suited to north-facing slopes with gradients of less than 15% (or 1:6). South-facing slopes impose a penalty on solar access; large lots and lowest densities are therefore best suited to south facing slopes.

Well orientated lots also enable the future home to have potentially greater roof space correctly orientated for solar hot water systems and photovoltaic arrays. A large expanse of north sloping roof space means that installing such systems is simplified and reduces the need for expensive modifications.

Source: SEDA, 2003

Concerns about the aesthetic impact of such devices is often reduced as ideally the north facing aspect should be the rear or side of the property and consequently, not visible from the streetscape.

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North-south or East-west?

In order to optimise solar access to buildings and private open space, street orientation should be predominantly north-south.

There are some practitioners who argue for the opposite to be optimal in terms of solar access i.e. street orientation should be predominantly east-west.

In order to settle the argument once and for all, the following table shows why north-south street orientation works better than east-west street orientation based on considerations of energy efficiency, thermal comfort, and solar access to private open space, energy efficient house plans and lot designs.

Considerations	North-South Streets East-West Lots	East-West Streets North-South Lots
Energy Efficiency	The long side of the building facing north receives more solar radiation to be harnessed for electricity generation and solar hot water collectors Lends itself to effective use of passive solar design to minimise energy usage to control thermal comfort	Unless the lots are wide and shallow, there is less exposure to the northern sun Does not lend itself to good passive solar design
Thermal Comfort	The shorter east and western boundaries of lots minimise exposure to the hot western sun - fewer windows to shade in summer - shorter exposed walls Easier to control northern sun to block out hot summer sun and let in winter sun with horizontal sun shading devices	With the long side of the building facing west, there is more exposure to the hot western sun, even with some shading by neighbouring buildings Harder to control low penetrating western sun - have to use vertical sun-shading devices
Solar Access to Private Open Space	Can focus on the north-facing side courtyard for principal private open space rather than the backyard, enabling the sunny backyard to be screened off for service area i.e. keep outdoor living areas between abutting neighbouring properties further separated resulting in improved visual and acoustic privacy Everyone gets a sunny, north-facing garden and family room regardless of which side of the street they live in	Properties facing the street to the north have shady private open space in the backyard Outdoor living in the abutting backyards of conventional house designs impact on visual and acoustic privacy of residents Can use house plans with side courtyards; but not efficient in terms of solar access – also exposes the long side of the houses to the undesirable western sun Can use C-plans with the main courtyard in the middle to get the sun into the courtyard – but this increases the length of external walls, i.e. expensive to build
Energy Efficient House Plans	More scope for development of new plan configurations that respond to energy efficiency, sustainability, increased visual and acoustic privacy Locating the main courtyard to the sunny side improves the interaction because mum doesn’t feel isolated in the kitchen while the kids are out in the backyard	Unless lot widths are sufficiently wide, it is not possible to get the sun into the family room with the conventional floor plan Can use C-plans with the family room in the lower part of the C to get the northern sun in – but this increases the length of external walls, i.e. expensive to build
Lot Designs	lends itself to effective zero-lot and zipper-lot subdivision layout make better use of shrinking lot sizes generated by the need to achieve better yields and affordability	North-facing lots need to be wider to compensate for difficulty in achieving solar access to the family room and private open space – i.e. affects yields Can not get the full benefit of zero-lot and zipper lot arrangement as the north-south zero-lotted blank wall cuts out half of the available sunlight hours either side of 12 noon.

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Solar setbacks and SAL

The guidelines for determining lot sizes and orientations have the principal aim of trying to ensure that the homes that will eventually be built on the lots have good access to sunlight. A key component of this is ensuring that solar setbacks are established on lots so that homes are not overshadowed by neighbouring properties, especially those to the northern boundary.

In response to this need, the Sustainable Energy Development Authority (SEDA), a NSW government authority, established the Solar Access for Lots (SAL) Guide. SAL provides a useful methodology for establishing solar setbacks and is described briefly here.

The SAL Guide is aimed primarily at low density developments and seeks to control the placement of a dwelling on a lot to ensure solar access rather than simply control the lot size directly. This is done by defining, at the subdivision stage, the dimensions of an area of each lot in the subdivision that cannot be built upon. This then controls the placement of dwellings on those lots at the development application stage.

These dimensions are influenced by the lot orientation and decisions regarding the height of a dwelling on the adjacent lot to the north. This tool does not provide a rating, but rather it ensures that all lots achieve defined minimum requirements for solar access.

Source: SEDA, 2005

This approach allows lot sizes to be ‘fine tuned’ to place moderate controls on the dwelling options on a given lot, to protect the solar access, whilst at the same time not affecting overall development yields. The control over lot dimensions remains in the hands of the subdivider as they are most aware of the dwelling types that would be placed on the lots. The tool encourages subdividers to make decisions on the footprint and height of dwellings to be placed on the lots at the subdivision application stage in order to deliver both reasonable yields for themselves and reasonable solar access for the lot purchaser. (SEDA, 2005)

The SAL Guide specifies that each lot in a subdivision has both a Flexible Solar Access Zone (FSAZ) and a Minimum Solar Access Zone (MSAZ):

• the FSAZ is the reserved part of the lot that may not be built on, thereby allowing solar access to glazing and private open space.
• the MSAZ is the minimum area of the FSAZ that may not be built upon. The MSAZ can be moved to any place within the FSAZ at development application stage to accommodate a range of house footprints. Once the MSAZ and the dwelling are located at development application stage, the FSAZ is no longer applicable and can be built upon.

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Building heights

It is important to ensure that homes do not infringe on the solar access provisions of a neighbouring property. The height of houses, especially those located on a property’s northern boundary, can be a critical factor in ensuring good solar access. The SAL Guide does provide guidance on this issue and requires that the dimensions of the solar access zones be increased where a double storey house is located to the north.

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Higher density and infill developments

Many of the principles outlined above are aimed at low density developments that are typical on fringe greenfield sites. Achieving good solar access for dwellings in higher density developments or infill sites is often a greater challenge. Regardless of the size or density of a development the basic principles of solar access and protection remain the same. How to achieve this in higher density developments is the real challenge.

Usually higher density or infill sites will have limited orientation opportunities. Overshadowing from neighbouring buildings and the likelihood of overshadowing from dwellings within the actual development is greatly increased. Nevertheless, careful planning of the location of buildings and trying to optimise the orientation potential of a site is critical.

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Case Study – K2 Apartments, Windsor, Victoria

The Victorian Office of Housing K2 project consists of 96 apartments in the inner Melbourne suburb of Windsor. The K2 Apartments are considered one of the most environmentally sustainable public housing developments in Australia.

The development's four apartment blocks were located on the site to maximise the solar access potential. The buildings are orientated on an east-west axis and the two larger towers were placed to the south of the lower towers to minimise overshadowing. The towers were slightly offset from each other to improve solar access and natural ventilation and the result is that all apartments are able to receive northern sunlight during the winter months.

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Case Study – Bila Village, Forest Hill, Victoria

Bila Village in Forest Hill, Victoria was a demonstration project undertaken between the state government and the Housing Industry Association, the principal residential building industry group. This estate was the first in Australia to integrate both advanced subdivision planning techniques with solar efficient estate design, ensuring that all lots provided passive solar design opportunities to future housing.

It is interesting to note that this development also incorporated 14 display homes which all achieved a 5 star energy rating (the maximum rating available), yet most of the additional homes that were constructed in the development followed traditional ’standard plans‘ provided by builders and failed to take full advantage provided by the site layout (Issac 1989).

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Case Study - Kingsley With The Sun, Wannaroo, WA

The Kingsley With The Sun development in Wannaroo, Western Australia, was developed in 1986 and was the first subdivision in Australia which sought to protect solar access. The development worked within existing street layout constraints and consequently had to control solar access through building and siting controls.

These controls included the use of solar and building envelopes for each site. These envelopes were determined through simulation of shadow projections at 9am and 3pm on the winter solstice. Three types of envelopes were created, a building envelope, a solar envelope and a 2-storey envelope.

Another control was a series of mandatory requirements for each dwelling, including R2 ceiling insulation, solar hot water system, cavity brick walls, concrete slab, 50% of windows facing north and appropriate shading of windows against summer sun.
Finally, the design and siting of dwellings had to be approved by a building design review committee in addition to the normal building permit approval.

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Key Issues

Benefits

The benefits of ensuring a high proportion of solar orientated blocks can include:

• Easier for builders to achieve the state and national energy efficiency requirements for homes as houses can take advantage of good orientation
• Reduced operating costs and improved internal amenity for home owners with less reliance on heating/cooling appliances and artificial lighting
• Greater outdoor amenity for residents with reduced overshadowing in backyard areas
• Improved opportunity to install solar hot water and photovoltaic systems as homes will be orientated correctly.
  

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Risks

Risks that may be associated with achieving optimal solar orientated lots include:

• Potentially reduced lot yields, particularly in higher density locations
• Larger lots required on south facing slopes and on the south side of east-west aligned streets
• Topography related issues (eg lots long access running up a slope, rather than across could cause problems with excavation, drainage, etc)
• Clashes with other sustainability initiatives, eg natural drainage paths that do not correspond with solar orientation requirements may impact on urban water management systems
• Small sites with boundaries not aligned with the preferred orientation.

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Savings

For the developer, there are not any potential savings that come from solar orientated lots. However, for the home builder and the home owner, savings are significant. The home builder should find that getting the required energy efficiency rating will be easier with a well orientated block. The rating tools used to assess the energy efficiency of a proposed design take into account the orientation of the home when calculating the energy requirements. A well orientated home will have lower energy requirements and should achieve a higher star rating. Consequently, savings in design time and building time can be expected.

The home owner will also benefit from a well orientated home. Reduced reliance on heating and cooling appliances should be achieved through greater use of solar gain during the winter months and good shading during the summer months. Reduced reliance on artificial lighting could also be expected as natural daylight will be easier to capture.

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Costs

In most situations there will be no additional cost for orientating blocks for solar access. Nevertheless, development sites are unique and can present a variety of challenges when trying to obtain the optimal site layout. The topography of the land is usually the biggest obstacle with south facing slopes a particular challenge. (Not just south facing (eg orientating to significant views). Ensuring that the majority of sites have good solar access may lead to slight reductions in lot yield which may have a cost implication. Of course, it can be argued that the necessary, increased lot sizes may attract a higher premium than smaller lots. In addition, the marketing of the solar benefits of the lots may also result in higher returns and quicker sales as community interest in sustainable development increases.

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Barriers

Barriers that may be associated with achieving optimal solar orientated lots include:

• Planning restrictions placed on certain street layout designs, in particular battle-axe style street layouts as opposed to traditional cul-de-sacs which can be beneficial in achieving well orientated blocks, but can pose safety and access problems with large service vehicles (garbage trucks, etc).

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Benchmarks

Several developments have mandated the requirement for well orientated blocks and several voluntary benchmarks have been established to guide developers in what is practically achievable. These include:

• The SEDA Solar Access for Lots (SAL), Guidelines for Residential Subdivision in NSW.
• The UDIA’s EnviroDevelopment standards require that 75% of lots meet the requirements of the SAL scheme to achieve their Energy section certification.

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Development phase actions

Feasibility

To achieve a comprehensive solar orientated development requires early assessment of its feasibility. Initial site topography details should provide an early indication as to the suitability of the proposed site to achieve solar orientated blocks. South facing slopes in particular can present difficulties.

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Planning

Initial planning will help determine how lots will be incorporated into the development. Many developments have a range of lot sizes which needs to be carefully determined to ensure good solar access.

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Lot Creation

As lots are developed it is important to inform builders and designers of the solar orientation opportunities that are integrated into the lot layout. Solar setbacks need to be adhered to and double storey dwelling implications on adjoining lots need to be monitored.

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Completion

Assess the effectiveness of the solar orientation principles.

• Have certain homes had solar orientation issues such as over shadowing?
• Have builders orientated homes effectively?
• Has the information campaign been successful?

Acknowledgements

Principal author:
Michael Ambrose

Contributing author:
Anne Miller

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Acknowledgements

Principal author:
Michael Ambrose

Contributing author:
Anne Miller