Building Design Principles for Excess Rainfall

Managing Rainwater Runoff

Traditional rainwater management practices include things like storm drains, pipes and retention ponds where the water can evaporate or be reclaimed. Under normal circumstances, this is more than sufficient to manage even a bad thunderstorm or hurricane.

As storms get more severe and start dumping more rain every year, these systems won’t be sufficient. When rainwater systems fail, flooding often results. City planners also have the added challenge of preventing rainwater runoff from entering the water table because it can carry all sorts of chemicals and other materials that could contaminate local drinking water.

Managing increased rainwater runoff will have a lot of components and require a lot of infrastructure upgrades—all in the midst of these increasingly severe storms that are causing flooding.

Replacing Non-Permeable Surfaces

Cities are colloquially known as concrete jungles because of the sheer number of paved surfaces. But this trend toward paving every possible square inch of ground has left many cities prone to flooding. 

The massive floods in Houston, Texas, in the wake of Hurricane Harvey in 2017 and in many Northeastern states after Hurricane Ida in 2021 show this all too well. Unpaved surfaces allow rainwater to trickle back down into the local water table. Concrete prevents this natural process and encourages flooding.

While reverting to an entirely unpaved and undeveloped landscape isn’t an option, switching to permeable pavers and other similar building technologies can allow the water to soak into the ground without creating flooding hazards. In addition to the rainfall benefits, research has found that these permeable surfaces require less salt in the winter to prevent icing and can trap heat that promotes thawing.

Versatility in Commercial Roof Design

Commercial building roofs are traditionally fairly flat because the peaked and vaulted roofs that are more common on residential buildings aren’t practical for the sort of square footage that most commercial properties demand.

If a commercial building’s roof doesn’t have the proper pitch—usually 1/4 inch for every 1 foot—water will likely begin to pond on the surface. Under normal conditions, ponding on commercial roofs is problematic because it can cause damage, water leaks, or provide a place for vegetation or mold to grow. Altering the design of the standard commercial roof won’t likely change much, but as rain levels increase, modifications will be necessary to stop ponding and other damage.

In warehouses and agricultural settings, alternatives to flat roof design can offer much-needed versatility. Designing storage facilities for environmentally-sensitive materials such as food or livestock requires investigating alternative structures like fabric coverings, which can be both thermally-conductive and engineered for water-resistance in inclement weather.

Green roofs are another option for some building design projects. Where a landscape provides no room for retaining ponds, the roof can provide essential square footage for managing rainwater runoff. Green roofs with rooftop gardens effectively absorb rainwater and control water flow, reducing the risk of this water ponding and leaking through traditional commercial roofs.

Whatever roofing design works best for a given application, waterproofing will be key. Waterproofing the building envelope can prevent both rain and groundwater from damaging a building, but it needs to be done cautiously to ensure it doesn’t affect the surrounding area or cause additional problems.

Creating Coastal Building Resilience

While coastal areas aren’t the only ones getting lashed by severe storms, as the 2020 derecho that caused devastation in Iowa proved, the coastal regions are prone to massive storms, storm surges, and rising sea levels. Buildings on the coast are already starting to feel the pinch of rising seas, but relocating isn’t always an option for commercial or residential property owners.

Structures on the coast need to be ready to handle large amounts of water, both from rain and storm surges. This is another place where waterproofing the building envelope could be valuable because it would enable building owners to come in and clean up the flood damage without worrying about mold in the walls or mildew in the drywall.

Investing in natural restoration projects in coastal areas can also help manage excessive rainfall. All of these natural features are designed to handle rain and storm surges. Human construction and development have simply interfered with those natural processes. Construction companies may not be prepared to contribute to projects like that, but restoration projects always need funding.

Designing Resilience is Key for Excess Rainfall

Upgrading existing infrastructure to prevent devastation and destruction is going to be crucial to protect people and products as seasonal rainfall shifts in many regions. 

The changes won’t be easy, especially considering the scale of some of the projects, but when strategic planning and a focus on rainwater management and sealed building envelopes will increase the resilience of a project—even in regions where seasonal storms and floodplains have a greater impact.