Five designs, one choice: testing wind comfort with ArchiWind while the massing can still move

Wind comfort problems are cheapest to fix while the massing can still move. In this worked example on a Manchester test scheme, five design options were tested with ArchiWind design runs, set up for fast feedback. Two made the shortlist and were confirmed with confirmation runs, the quality used for reporting to planning authorities. The chosen design kept its full height and made the street calmer without giving up the plaza.

Too often, wind comfort is checked after the building shape is fixed. By then the only answers left are expensive: a redesign, or mitigation the design team never wanted. ArchiWind, NablaFlow’s site-specific wind analysis for the built environment, shows how wind moves around a design and how comfortable each outdoor space will be for people.

This example shows the alternative, step by step. Thomas Michelon, Head of Product for ArchiWind, set up a test scheme in Manchester and laid out the process ArchiWind’s architect users follow in early design: the general massing in place, the outer form still open, and wind in the loop from the first sketch. One design idea, rounding a corner, made the street windier. ArchiWind showed it within the hour, and it turned out to be the most useful step of all.

Two of the five design options earned a confirmation run. The rounded corner made the street worse, and finding out why pointed the way to the chosen design.

The study at a glance
Scheme	Test scheme, Manchester (worked example)
Comfort criterion	Lawson 2001
Zones	Zone 1: plaza inside the complex · Zone 2: street beside it · Zone 3: building corner next to the street
Design runs (Draft quality in ArchiWind)	5 design options, 8 wind directions, 25 cm grid, under 1 hour each
Confirmation runs (Detailed quality in ArchiWind)	2 designs, 16 wind directions, 12 cm grid, up to 3 hours each
First design to chosen design	About 3 days elapsed, including design time between runs

Step 1: Decide what each space is for, before you simulate anything

The outcome of a wind study is set before the first run. What a space is used for decides how much wind it can take. This study uses the Lawson 2001 comfort criteria. Each spot on the comfort map gets the calmest activity it is suitable for, based on the mean wind speed 1.5 m above the ground that is not exceeded 95% of the time.

Class	What people can do there	Mean wind speed	Colour on the map
A	Calm enough to sit	up to 4 m/s	dark blue
B	Calm enough to stand	up to 6 m/s	light blue
C	Comfortable for strolling	up to 8 m/s	yellow
D	Only comfortable for walking through briskly	up to 10 m/s	orange
E	Uncomfortable for any use	above 10 m/s	red

1. Mark the zones. In this scheme, two zones are critical. Zone 1, the plaza at the heart of the complex, should be calm enough to stand (class B or better). Zone 2, the stretch of street beside it, must stay comfortable for people on foot. Zone 3 is the building corner next to Zone 2. It is not a comfort target itself, but it is where the first fix was tried. Other edges of the site matter less: a service street, for example, can tolerate conditions only comfortable for walking through briskly (class D).

2. Read the planning requirements. They usually come in one of two forms:

• Existing site: the new building must leave pedestrian comfort the same or better than today, shown with a before/after comparison.
• Empty site: the authority sets a rule for the surroundings, for example no area that is only comfortable for walking through briskly (class D) or worse within about 100 m of the building.

ArchiWind can report against Lawson 2001, Lawson LDDC, Lawson 1978, Lawson Beaufort, NEN 8100 (Netherlands) and IS 5281 (Israel). Choose the criterion your planning authority uses, and check that it matches the legend on every map you share.

Skip this groundwork and every later simulation answers the wrong question.

Step 2: Compare design options with design runs

This is the window that matters. Your massing exists in Rhino and the ground-floor surfaces are known, but the outer form and the layout can still move. Each design option goes into a design run, ArchiWind’s fast-feedback quality (called Draft in the app): 8 wind directions on a 25 cm grid, back in under an hour. Check each one against Zones 1 and 2 only.

Design 1: Zone 1 calm, Zone 2 too windy. The first scheme kept the plaza sheltered. But it pushed wind onto the street, so one of the two critical zones missed its target.

Design 2: lower the building. Reducing the height cleared most of the problem in Zone 2. It is the textbook fix: a lower facade brings less wind down to street level. It is also a fix the brief often rules out, so the question became how to get the same result at full height.

Design 3: round the corner. Zone 2 got worse. Softening the corner at Zone 3 seemed logical. Instead, wind accelerated around the building from the south and other directions, and Zone 2 became windier than in Design 1. The design run showed it in under an hour, and it taught the most.

The diagnosis: read the wind one direction at a time

The step between the rounded corner and the working design is the easiest one to skip. The combined comfort map shows where it is uncomfortable. It does not show why.

After Design 3, the next check is the wind rose: the site’s record of how often the wind blows from each direction and how strongly. It shows which strong winds are most frequent. The flow is then reviewed one wind direction at a time, with particle tracing on to see how the air moves around the building.

Here, three directions did the damage: west, south-west and south. Wind from the west in particular hit the facade and was pushed straight down into Zone 2. This is downwash, one of the main ways a tall building makes the street below it windy.

That changes the problem. Instead of “fix the uncomfortable patch”, it becomes “stop the wind from those three directions reaching Zone 2”. Designs 4 and 1-modified were both answers to that sharper question.

The per-direction results come with every ArchiWind run, so this step needs no extra simulation.

Design 4: open a path for the wind. Rather than squeezing the flow between volumes, this version let it through. The worst spots in Zone 2 disappeared, but the plaza in Zone 1 became slightly windier throughout. It traded one strong problem for a mild one spread across the site.

Design 1 modified: break the wind on the facade. The fix kept the original massing and full height. Wind-breaking elements went on the exposed facades, where they interrupt the downwash before it reaches Zone 2. In this test scheme they are a concept to show the principle, not a detailed design. Zone 1 stayed calm and most of the discomfort in Zone 2 was gone. At first glance the elements read as balconies.

Step 3: Confirm the two strongest designs with confirmation runs

Design runs are for comparing options. Decisions that go to a planning authority need a finer result. The five options narrowed to two candidates: Design 1 modified and Design 2. Both went into confirmation runs, ArchiWind’s reporting quality (called Detailed in the app): a 12 cm grid instead of 25 cm, and 16 wind directions instead of 8, in up to three hours.

With both results side by side, the comparison came down to Zones 1 and 2. Design 1 modified kept Zone 1 calm, removed most of the discomfort in Zone 2 and kept the original height. Design 2 had cleared most of Zone 2 in its design run, but only by giving up height. Design 1 modified is the design to take forward.

Its confirmation run comes with a report that ArchiWind generates automatically, describing the methodology and the simulation results. In the Nordics, this report is used as evidence for municipal approval. Where the authority requires a formal wind assessment, as in England, the design goes to the wind consultant already tested against real alternatives.

What this changes for your practice

The result is a better building at street level: people can walk past the corner without the wind coming down the facade at them. The fix came from design, tested while the massing could still move, rather than from mitigation added late.

• No late surprises. Comfort problems show up while a sketch is cheap to change: a design run is back in under an hour.
• You keep control of the design. Options are tested in-house as the design develops. The wind consultant then confirms a design instead of discovering its problems.
• A stronger application. The chosen design arrives with the process that led to it, and in the Nordics with a report the municipality can use.

The lesson from the rounded corner holds for any scheme: intuition about wind is often wrong, and the cost of finding out should be a design run, not a redesign.

Test your next scheme while it can still change. Run your first wind analysis by clicking the button below