Wind-Driven Rain

Managing rain accumulation and keeping open spaces dry through thoughtful design

Wind and rain may interact with a building’s form to cause rainwater to move and accumulate in unexpected ways. Good design for open spaces and rainwater management takes these patterns into account.

rain hitting side of umbrella

Open spaces. 

A growing trend favors naturally ventilated public spaces, especially in warmer climates. This trend is driving architectural designs to be more open to the environment. Such spaces benefit from natural light, fresh air and overall higher user satisfaction.

However, such spaces are also more exposed to the elements. The wind can carry rain into exposed areas, sometimes in unexpected ways. And architecture can worsen the problem by shaping unfavorable airflows.

The results can be unpleasant, costly, or dangerous. Patrons get damp and annoyed; floors get dangerously slippery; electrical circuitry is exposed to water. Whatever the effect, the overall usability of the space is compromised. The good news is that carefully placed adjustments can prevent most of these effects.

Rainwater management. 

Wind–rain interactions can affect drainage systems, rainwater harvesting systems, cladding systems and roof loads. Depending on the local climate, smart tweaks to your building’s orientation and form could make a big difference to your capital and operating costs for managing rain and its effects.

Our service

We show you where rain will go, how often it will go there, and how to make it go somewhere else—without creating new issues. We look for holistic solutions to make sure your design works well rain or shine. Often we’re able to provide early feedback using simple calculations, but for novel designs we can perform full-scale tests to ensure accuracy.

We first create a physical picture of how rain could enter (“infiltrate”) your project, working with the specifics of your location and design. To do this, we apply our world-leading expertise in meteorology, fluid dynamics and the physics of airborne particles. Depending on your needs and the possible issues, we will simulate airflow and raindrop travel to quantify infiltration problems. In addition, we may do physical simulations in our wind tunnels.

We test our proposed solutions in the same simulations, and we seek advice of colleagues throughout the company to make sure the changes don’t cause new problems elsewhere. For example, our wind engineers can make sure a bus shelter won’t create unpleasant new winds for nearby pedestrians. We can also do calculations for guttering and runoff based on the same high-quality meteorological statistics.

The results are presented in terms of risks, so you can make informed decisions about solutions and tradeoffs.

Related services

We also consult on stormwater management, pedestrian comfort and safety, and cladding performance