Cool Streets

CS1: Shade

7 default credit points (Climate Zones 2 and 4)

3 default credit points (Climate Zones 5, 6, 7 and 8)

Outcome

Shade (natural and built) within street reserves lowers surface radiative temperatures, promotes ventilation, and improves Human Thermal Comfort.

Criteria

Tree canopy cover at maturity (measured as % of street reserve):

Note: Targets exclude intersections. For existing streets, the above targets only apply if greater than the existing (pre-refurbishment) tree canopy cover, otherwise no-net loss of tree canopy cover is the acceptable target.

And;

Shading of high use spaces:

• >80% shade cover (measured in plan) of footpath or shared use spaces within street reserves.
• On-grade carparks: one medium tree (8m diameter canopy at maturity) per four car parking spaces. The tree is to be in a planted within a deep soil zone of >13 m² - the equivalent of a car parking bay area.

Guidance

• Selection and placement of shade solutions within streets should consider peak-use times to ensure shade maximises solar UV protection when it is needed most.
• Tree species selection to suit in-situ soil conditions and resilience to high heat stress having regard to projected future extreme heat days due to climate change (refer to Adapt NSW's Regional Climate Change Snapshot Reports for a summary of projected changes to extreme heat days, temperatures and summer rainfall in your region).
• A variety of suitable tree species is preferred to increase the urban canopy roughness through different tree heights and foliage types.
• Guidance on the best tree species for a given geography based on various planting factors including future climate is available on the https://www.whichplantwhere.com.au website.
• Use evergreen trees for areas that will benefit from year-round shade.
• Use deciduous trees where sunlight is desirable in winter.
• Consideration of safety is paramount with species selected to minimise risk to public safety.
• Access to deep soils supports healthy trees. Recommended minimum deep soil areas:
  • Small Trees (6 metre canopy diameter at maturity): 14m² in sandy loam soils; 23m² in clay soils.
  • Medium Trees (8m diameter canopy at maturity): 18m² in sandy loam soils; 30m² in clay soils.
  • Large Trees (≥12m diameter canopy at maturity): 26m² in sandy loam soils; 43m² in clay soils.
• Ensure a secure water supply is available during extended dry periods to provide the minimum sustaining irrigation needs of each tree species (see CS2).
• Provide active management of younger trees to support crown development.
• Develop and apply long term strategies to transition from built shade to an increased proportion of natural shade as canopy increases in size and density.
• If installing shade sails as part of built shade solutions, make sure to choose fabric that has a UV Effectiveness (UVE) rating of 80% or more.
• A test if shade is high quality or not on a clear day is the amount of blue sky you can see (sky view factor) while underneath it. The less blue sky you can see, the better protection from solar UV radiation.

Evidence Requirements

Landscape plan showing canopy cover at maturity as % of street reserve area for all streets.

Science Rationale

• Street reserves and on-grade carparks will often have a high percentage of heat absorbing surfaces such as bitumen, concrete and paving. Without shade, these surfaces can heat to very high surface temperatures on hot summer days increasing mean radiant temperature and reducing Human Thermal Comfort.
• Studies (42) have shown shade from street trees can modify street micro-climates to improve the comfort of pedestrians and lower local air temperatures. Percentage canopy cover, street orientation and aspect ratio (W:H) interplay to determine the magnitude of urban heat benefits.
• A study of microclimatic variation across the City of Parramatta during the summer of 2018/19 showed a street with 30% tree canopy cover experienced only 5 days of local air temperatures greater than 40°C whereas a nearby street where canopy cover was just over 10% the local air temperatures soared above 40°C on 13 days (18).
• A study comparing the micro-climate of two residential streets with similar aspect ratio (H:W) in East Melbourne, where one street had very little tree canopy cover (12%) and the other had a good tree canopy cover (45%), showed during hot summer conditions the local air temperature in the street with more trees was 0.2-0.6 °C cooler than the street without many trees (42). The street with more trees was also up to 0.9 °C cooler during the morning as the trees delayed surface heating. Moreover, heat stress (Human Thermal Comfort) was lower in the street with trees.

Related Credits

• UD5 - Retention of existing tree canopy
• UD6 - Water Sensitive Urban Design
• CS2 - Irrigation
• INV2 - Data collection and Analysis

References

(18) Pfautsch, S.' and Rouillard, S. Benchmarking Heat in Parramatta, Sydney's Central River City, 2019.

(42) Coutts, A. M., Tapper, N. J., Beringer, J., Loughnan, M. & Demuzere, M. Watering our Cities: The capacity for Water Sensitive Urban Design to support urban cooling and improve human thermal comfort in the Australian context. 2013, Progress in Physical Geography.