A high-rise tower does not merely occupy space — it actively reshapes the wind, shading and thermal environment of the streets and courtyards around it. As Israeli cities densify through Tama 38 and Pinui-Binui programmes, planning committees are placing increasing weight on microclimate analysis as a condition of permit approval. CFD (Computational Fluid Dynamics) simulation is no longer specialist territory: it is standard practice for any building project above eight storeys in major urban authorities.
When a tall building is inserted into an existing urban fabric, it creates a complex set of aerodynamic effects that extend far beyond its own footprint. The building acts as an obstacle to the prevailing wind, forcing the flow to accelerate around its sides and down its windward face — the well-documented "downwash" or "downdraught" effect — and creating a turbulent wake on the leeward side. In a poorly designed scheme, ground-level wind speeds in the lee of a tower can reach 10–12 m/s even when regional wind conditions are moderate, creating conditions that are uncomfortable for pedestrians and potentially dangerous near building entrances, outdoor dining areas and children's play spaces.
The building also casts shadows. Depending on its orientation and massing, a new tower can reduce direct sunlight access to neighbouring buildings for several hours per day, affecting both the comfort of outdoor spaces and the energy performance of adjacent buildings. In a city like Tel Aviv where residential balconies and rooftop terraces are primary living spaces for much of the year, shadow impact is a quality-of-life issue with direct relevance to apartment values in the surrounding neighbourhood.
Finally, the building changes the thermal microclimate at street level. Dense urban development replaces permeable vegetation with impermeable hard surfaces, reduces sky view factor (the proportion of sky visible from a point at ground level), and concentrates waste heat from air conditioning systems. The cumulative effect — the urban heat island — can raise street-level temperatures by 2–4°C relative to the rural surroundings, increasing cooling demand for all buildings in the cluster and worsening outdoor thermal comfort during summer evenings.
The Lawson criteria, developed by the British Standards Institution and widely adopted internationally, provide a pedestrian wind comfort classification framework based on exceedance frequency of wind speed thresholds. The framework defines five use categories — Sitting (calm, for outdoor café use), Standing (for waiting and shopping areas), Walking Slow (for casual pedestrian routes), Walking Fast (for main pedestrian thoroughfares), and Uncomfortable (where wind speeds exceed comfort thresholds more than 20% of the time) — and a safety threshold beyond which conditions are considered dangerous.
Each category is defined by the percentage of hours per year in which the mean wind speed at pedestrian level exceeds the threshold value for the category (typically 4 m/s for Sitting, 6 m/s for Standing, 8 m/s for Walking Slow, and so on). A CFD assessment maps these exceedance probabilities across the entire ground-level study area, typically extending one to two building heights beyond the project boundary, and identifies zones where the wind environment fails the target criterion for the intended use.
Israeli planning authorities do not yet have a single national standard mandating Lawson criteria for all projects, but the Tel Aviv-Jaffa Building Committee, the Herzliya Local Planning Committee, and several other municipal authorities have adopted wind comfort assessment as a routine requirement for buildings exceeding eight storeys or where outdoor public spaces are created as part of the development. Non-compliance with Lawson criteria — or failure to conduct an assessment when required — can delay permit approval by months while a supplementary assessment and mitigation design are prepared.
Why mitigation is often cheaper than redesign: CFD modelling at early design stage allows wind-mitigation measures — windbreak canopies, landscaping, building edge articulation, through-building passages — to be incorporated into the architectural design without structural changes. When wind assessment is commissioned at the permit stage with a fixed design, the options narrow significantly and mitigation measures may require expensive architectural amendments or planning negotiations.
A CFD wind study for an Israeli urban development project involves several distinct steps. First, the study area is established — typically a 500–1,000 m radius around the building, modelled with all existing buildings represented accurately in the computational domain. Wind rose data from the Israeli Meteorological Service (IMS) station nearest the site is processed to establish the frequency distribution of wind speeds and directions across all 16 compass sectors.
The CFD computation runs the fluid dynamics equations across the three-dimensional building and terrain geometry for each wind direction, generating a map of wind speed ratios (the ratio of predicted pedestrian-level speed to the reference height speed) across the study area. These ratios are then combined with the wind rose data to calculate Lawson exceedance probabilities at each assessment point. The entire process, from model setup to final mapped results, typically takes 4–8 weeks for a mid-rise residential project and 8–12 weeks for a complex mixed-use tower scheme.
Software platforms used for Israeli planning submissions include ANSYS Fluent, OpenFOAM (open source), Autodesk CFD and STAR-CCM+. The choice of solver is less important than the turbulence model used (the standard k-ε or the more accurate Realizable k-ε are preferred for pedestrian wind studies), the quality of the geometry import, and the validation of the mesh resolution against published benchmark test cases. Israeli planning authorities are increasingly requesting evidence of mesh sensitivity analysis and comparison with wind tunnel data in the CFD submission report.
Israel's two primary urban renewal frameworks — Tama 38 (earthquake strengthening with density bonus) and Pinui-Binui (demolish-and-rebuild) — create particular microclimate challenges because they typically introduce significantly taller buildings into an existing low-rise residential fabric. A Tama 38 project adding three floors to a five-storey building may not trigger a wind study requirement; a Pinui-Binui project replacing an eight-storey block with a twenty-storey tower almost certainly will.
The sensitivity of Tama 38 and Pinui-Binui projects to microclimate assessment is heightened by their location within established residential neighbourhoods, where existing residents and local committees are often vocal about quality-of-life impacts. A wind assessment that demonstrates acceptable pedestrian conditions, or a shading analysis that shows minimal impact on solar access to neighbouring apartments, can be decisive evidence in securing local committee support during the objection period.
Solar access analysis — modelling the number of hours per day that existing neighbouring apartments will receive direct sunlight after the new building is erected — is a growing area of planning requirement in Tel Aviv. The city's local plans include requirements for minimum solar access durations on habitable room facades, and violations are a common basis for planning objections. Razore Engineering provides solar access modelling using validated solar simulation tools as part of its standard environmental report for urban renewal projects.
Within the development itself, shading analysis serves two complementary purposes. For the building's energy performance under SI 5281, shading of windows and facades reduces cooling load and glazing solar heat gain — a positive contribution to thermal performance. For the quality of outdoor spaces — courtyards, gardens, play areas, lobbies — shading analysis ensures that public areas receive adequate direct sunlight for the use intended.
The standard Israeli planning requirement for residential outdoor spaces is a minimum of 3 hours of direct sunlight per day on at least 50% of the open space area during the winter solstice (21 December). This is a generous criterion by northern European standards but one that can be difficult to achieve in a dense Tel Aviv infill project where the surrounding streetscape already limits sky access. Roof terraces and elevated amenity decks — increasingly specified in premium residential projects — are often required to achieve the winter sunlight criterion when ground-level courtyards cannot.
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