Sky view factor (SVF) in urban planning | ENVI-met from One Click LCA

The Sky View Factor (SVF) is a key metric in urban climate research, indicating how much of the sky is visible from a given location. It directly impacts temperature regulation, ventilation, and air quality — factors essential for creating comfortable and sustainable urban environments. This article explains what SVF is, how it’s measured, and why it’s crucial in city planning. It also explores how tools like ENVI-met help integrate SVF with other environmental variables to design climate-resilient cities.

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Sky view factor (SVF) in urban planning | ENVI-met from One Click LCA

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What is the sky view factor (SVF)?

The Sky View Factor (SVF) is a critical parameter in urban climate studies. It represents the proportion of visible sky from a specific location. It ranges from 0 (completely enclosed spaces like narrow alleys or dense tree canopies) to 1 (wide-open areas such as open fields). SVF is a key factor in urban climate studies, influencing temperature, radiation balance, ventilation, and overall thermal comfort.

SVF in urban climate and planning

In densely built environments, the Sky View Factor (SVF) plays a crucial role in urban climate and air quality. A common assumption is that low SVF tends to trap heat, contributing to the urban heat island (UHI) effect, where cities remain warmer than surrounding rural areas. Narrow streets and enclosed spaces with low SVF retain heat at night, slowing down cooling and exacerbating thermal discomfort. In contrast, higher SVF areas allow for better heat dissipation and natural ventilation, helping to regulate temperatures more effectively. Urban planners and architects leverage these principles to design climate-resilient cities, optimizing street layouts, building heights, vegetation placement, and shading strategies. Beyond temperature regulation, SVF also influences air circulation and quality. Areas with low SVF tend to trap pollutants due to reduced wind flow, leading to poorer air quality. Meanwhile, high SVF environments promote better air exchange, improving overall air quality and livability. By integrating SVF considerations into urban design, cities can create healthier, more sustainable environments that balance thermal comfort, ventilation, and air quality.

How is SVF measured?

There are several ways to measure SVF:

Basic geometric calculations using building and street dimensions.
Fish-eye lens photography, where images are analyzed to determine sky visibility.
Advanced 3D simulations, such as those performed with ENVI-met, which provide highly accurate SVF assessments and urban climate modeling.

Fig 1. Daily development of thermal comfort (Physiological Equivalent Temperature) in a model with high sky view factor

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Fig. 2 Daily development of thermal comfort (Physiological Equivalent Temperature) in a model with low sky view factor

A holistic approach to urban climate

While SVF is important, it does not work in isolation. Urban climate is influenced by multiple factors, including:

Building materials and surface albedo: Affect heat absorption and reflectivity, impacting thermal comfort.
Vegetation and water bodies: Provide natural cooling through shading and evapotranspiration, helping to regulate temperature and humidity.
Wind patterns: Influence ventilation, pollutant dispersion, and overall urban airflow.
Human activities: Energy use, traffic emissions, and artificial heat sources add to local temperature variations.

A city optimized solely for SVF without taking into account impacts of materials, airflow, and greenery may still experience environmental challenges. A holistic approach considers all these elements to create sustainable and livable urban spaces. That’s where ENVI-met can fill the gap.

ENVI-met: a comprehensive urban climate tool

ENVI-met is a 3D microclimate simulation tool that integrates SVF with other urban climate factors. It helps planners and researchers:

Model SVF and solar radiation to optimize shading and heat distribution.
Simulate wind flow and turbulence to improve ventilation.
Analyze building and surface heat dynamics for better thermal comfort.
Assess vegetation effects on urban cooling through evapotranspiration.

By using ENVI-met, urban designers can predict how changes in building layout, green infrastructure, and materials will impact the microclimate, leading to more climate-adaptive city planning.

Conclusion

The sky view factor (SVF) is a valuable metric in urban climate studies, but it must be considered alongside other environmental factors. By leveraging advanced tools like ENVI-met, urban planners can design cities that balance temperature regulation, ventilation, and overall livability, creating sustainable and climate-resilient urban spaces.