Resilient by Design: Structural Solutions for Rising Coastal Stakes

For structural engineers working on coastal projects, the challenge is no longer just about wind loads or salt spray. Rising sea levels and more frequent storm surges demand a fundamental rethinking of how we design foundations, frames, and envelopes. This guide is for experienced practitioners who already know the basics of coastal construction. We focus on the structural decisions that separate resilient buildings from those that require major repairs after a single event. We will cover foundation strategies, load path continuity, material selection, long-term maintenance realities, and the often-overlooked question of when not to use a particular approach.

Where the Real Pressure Builds: Field Context for Coastal Structural Design

The stakes in coastal structural resilience are not uniform. A building on a high bluff with stable soils faces different threats than one on a low-lying barrier island. The most critical field context is the combination of hydrostatic and hydrodynamic loads during a storm surge. Hydrostatic loads come from standing water pushing against walls and floors, while hydrodynamic loads result from moving water, which can exert forces many times greater than wind alone. We also have to consider erosion and scour around foundations, which can undermine a structure even if the building itself remains intact above grade.

Understanding Site-Specific Surge and Wave Action

Designing for surge requires more than just looking at FEMA flood maps. Those maps give base flood elevations, but they often do not account for wave setup, runup, or the effects of local topography. In practice, we have seen projects where the mapped stillwater elevation was accurate, but wave action added an extra three feet of dynamic load. This is especially critical for buildings near the open coast or in large bays where fetch allows waves to build. We recommend using site-specific wave modeling or at least applying the ASCE 7 wave load provisions with conservative assumptions about debris impact.

The Role of Scour and Erosion in Foundation Design

Scour is one of the most underestimated failure mechanisms. During Hurricane Sandy, many buildings that survived the surge itself were later condemned because their piles were exposed and damaged by scour. The challenge is that scour depth depends on soil type, flow velocity, and duration of inundation. In sandy soils, scour can reach depths of six feet or more in a single storm. Designing piles with sufficient embedment below the maximum scour depth is essential, but we also need to consider that multiple storms over a building's life can cause progressive scour. One approach is to use a sacrificial scour layer or to design piles with a larger diameter near the mudline to resist lateral loads after scour occurs.

Foundations That Confuse Even Seasoned Engineers

Foundation selection for coastal buildings often leads to disagreement among experienced engineers. The confusion usually stems from conflicting requirements: the need for elevation to avoid flooding, the need for deep foundations to resist scour, and the need for lateral load resistance from wind and waves. Three common foundation types—shallow spread footings, deep piles, and mat slabs—each have specific failure modes that are not always obvious.

Shallow Footings in Coastal Zones: A Risky Bet

We sometimes see shallow footings used for small coastal structures like beach pavilions or boardwalk buildings. The assumption is that the building is light and the soil is competent. But in a surge event, buoyancy can lift the building if the footing is not adequately anchored, and scour can remove the soil beneath the footing, leading to differential settlement. Even if the building is elevated on a stem wall, the footing itself must be deep enough to resist overturning from wave loads. For most coastal applications, shallow footings are not recommended unless the site is protected by a seawall or the building is designed to be sacrificial.

Pile Foundations: Depth vs. Lateral Capacity

Pile foundations are the go-to solution for coastal buildings, but the design details matter greatly. Driven timber piles are common because they resist corrosion and are relatively low cost, but they have limited lateral capacity. Concrete piles offer more strength but can crack if not properly reinforced against bending moments from wave loads. Steel piles are strong but require corrosion protection in the splash zone. The real confusion arises when engineers try to optimize pile spacing and embedment depth. Deep piles that extend 40 feet into the ground provide excellent vertical capacity, but if they are too slender, they may not resist the lateral forces from waves without excessive deflection. We have seen projects where the piles were driven deep enough for scour but were too flexible, causing the building to sway enough to damage interior finishes and utilities. A better approach is to use batter piles or to increase pile diameter in the top 10 feet to improve lateral stiffness.

Mat Slabs and Floating Foundations

Mat slabs can work for buildings on very soft soils, but they are vulnerable to uplift if the water table rises above the slab. In coastal areas, the water table can rise several feet during a storm, creating hydrostatic uplift pressures that can crack or lift a mat slab if it is not designed as a buoyant foundation. Some engineers use a floating foundation concept where the building is designed to rise with the water, but this requires careful detailing of utility connections and access. For most buildings, a mat slab is better suited to interior areas of a site where the water table is controlled by drainage, not directly exposed to surge.

Load Path Patterns That Usually Work

Resilient coastal structures share common load path patterns that have been proven in hurricanes and nor'easters. These patterns focus on continuity from the roof to the foundation, with redundancy at connections.

Continuous Load Path from Roof to Foundation

The most reliable pattern is a continuous load path where every element—roof diaphragm, walls, floor diaphragms, and foundation—is connected with rated connectors. In wood-frame construction, this means using hurricane ties at every rafter-to-wall connection, hold-downs at shear wall ends, and anchor bolts at the sill plate. In steel or concrete frames, it means welding or bolting beam-to-column connections that can transfer moment and shear without relying on friction. The key is that the load path must be designed for both uplift and lateral forces simultaneously. We often see designs where the lateral system is adequate for wind, but the uplift connections are undersized because the engineer assumed that dead load would resist overturning. In a surge event, buoyancy can reduce the effective dead load, so uplift connections must be designed for the net uplift force with no contribution from dead load.

Redundancy Through Multiple Lines of Defense

Another pattern that works is providing multiple lines of defense. For example, the primary lateral system might be a series of shear walls, but we also design the moment frames at the building perimeter to pick up load if the shear walls are damaged. Similarly, the foundation might have both deep piles and a grade beam that can distribute loads if one pile fails. Redundancy is especially important in coastal zones because a single event can damage multiple components. We have seen buildings where a wave broke a single shear wall, and the entire lateral system collapsed because there was no alternative load path. Designing for progressive collapse resistance is becoming standard in high-risk areas.

Elevated Structures with Breakaway Walls

For buildings in V zones (velocity wave zones), elevating the structure on piles or columns with breakaway walls below is a proven pattern. The breakaway walls are designed to fail under wave loads, allowing water to flow through without transferring significant force to the structure. The challenge is that breakaway walls must be designed to fail at a specific load, but they also need to resist wind loads during non-storm conditions. This requires careful detailing of the connections and the wall panels. We recommend using frangible connections that fail in a predictable manner, such as shear pins or breakable clips, rather than relying on the wall itself to break apart.

Anti-Patterns and Why Teams Revert to Them

Despite known best practices, many coastal projects still incorporate design choices that undermine resilience. Understanding why teams fall back on these anti-patterns can help us avoid them.

Relying Solely on Sacrificial Cladding

One common anti-pattern is designing the building envelope with sacrificial cladding that is intended to be replaced after every major storm. The idea is that the structure itself is robust, but the cladding will take the hit and can be easily swapped out. In practice, this rarely works as planned. The cladding often fails in a way that damages the underlying structure, or the cost of replacement is so high that the owner abandons the building. We have seen cases where metal panels peeled off and struck adjacent buildings, causing liability issues. The better approach is to design the cladding to resist the design event with some margin, using materials that are impact-resistant and corrosion-proof.

Ignoring Scour in Favor of Deep Piles Alone

Another anti-pattern is assuming that driving piles to a deep bearing stratum automatically protects against scour. Deep piles can resist vertical loads even after scour, but they may lose lateral capacity if the soil around the pile is removed. The pile becomes a long column with reduced buckling resistance, and the building can sway excessively. Teams sometimes revert to deep piles because they are easier to design than a scour protection system, but the result can be a building that survives the surge but is uninhabitable due to structural damage. We recommend combining deep piles with a scour countermeasure such as riprap or a collar that limits scour depth.

Over-Designing for Uplift While Under-Designing for Lateral

We have seen projects where the engineer was so focused on uplift from buoyancy that they neglected lateral loads from waves and debris. The result is a building that stays anchored to the ground but is pushed off its foundation laterally. This anti-pattern often arises because uplift calculations are straightforward (buoyant force = volume of displaced water), while lateral loads require more complex analysis of wave forces and debris impact. Teams may also assume that the lateral system designed for wind is sufficient for waves, but wave loads can be several times higher than wind loads on the same structure. The fix is to perform a combined load analysis that includes both uplift and lateral forces simultaneously, and to check the foundation for sliding and overturning under the worst-case surge scenario.

Maintenance, Drift, and Long-Term Costs

Resilient design does not end with construction. The long-term performance of a coastal structure depends on maintenance, monitoring, and the ability to adapt to changing conditions. We need to consider how materials degrade, how foundations settle, and how the building's performance drifts over time.

Corrosion and Material Degradation in the Splash Zone

The splash zone—the area between the high tide line and the top of wave runup—is the most corrosive environment for any structure. Steel piles and connectors in this zone can lose section at rates of 0.1 inches per year or more if not protected. Concrete can spall due to chloride ingress, and wood can rot if not treated properly. The long-term cost of corrosion protection is often underestimated. We have seen projects where the initial cost of stainless steel connections was rejected in favor of galvanized steel, only to have the connections fail within 10 years. The maintenance cost of replacing corroded connectors can be higher than the initial savings. For critical connections in the splash zone, we recommend using stainless steel or a combination of hot-dip galvanizing and a sacrificial coating system that can be inspected and replaced.

Foundation Settlement and Differential Movement

Over time, foundations can settle due to consolidation of soft soils or due to cyclic loading from waves. Differential settlement can cause cracks in walls, floors, and roofs, which then allow water intrusion and further damage. Monitoring settlement is important, but many coastal buildings lack access for inspection. We recommend installing settlement markers at the corners of the building and surveying them annually. If settlement exceeds a threshold, the foundation may need underpinning. The cost of underpinning is significant, so designing the foundation with a factor of safety against settlement is more economical than retrofitting. In areas with highly compressible soils, consider using deep foundations that extend to a bearing stratum, even if the building is light.

Adapting to Sea Level Rise

Sea level rise means that the design conditions today will be different in 30 years. A building designed with a ground floor elevation of 10 feet NAVD88 might be adequate now, but if sea level rises by 2 feet, the same building will have a lower effective freeboard. This drift in performance is a long-term cost that is often ignored. Some jurisdictions now require a sea level rise allowance in the design flood elevation, but many do not. We recommend adding at least 2 feet of freeboard above the current base flood elevation, and designing the foundation so that the building can be jacked up in the future if needed. The cost of adding a jacking beam or a reinforced concrete grade beam that can support lifting is small compared to the cost of retrofitting later.

When Not to Use This Approach

Not every coastal building needs the full suite of resilient design measures. There are situations where a simpler, less robust approach is appropriate, and trying to apply a high-resilience design can be counterproductive.

Low-Occupancy or Temporary Structures

For structures like beach cabanas, storage sheds, or seasonal kiosks that are not occupied during storms, it may be more cost-effective to design them as sacrificial. The building can be designed to fail in a controlled manner, with the expectation that it will be replaced after a major event. This approach saves money on foundation and connection costs, but it requires that the owner accept the risk and have a plan for replacement. We have seen projects where a sacrificial structure was designed with breakaway connections and minimal foundations, and it performed well because the debris was small and did not damage adjacent buildings. The key is to ensure that the sacrificial structure does not become a hazard to others.

Buildings with Short Design Life

If a building is expected to be in service for only 10 to 15 years, it may not be economical to design for a 50-year storm event with sea level rise. Instead, the design can focus on the current flood hazard with minimal freeboard. However, the building should still be designed to resist wind loads and to be safe for occupants during a storm. We recommend using a performance-based approach where the owner decides the acceptable level of risk. For example, the building might be designed to resist a 10-year storm without damage, but to be repairable after a 50-year event. This requires a clear understanding of the owner's risk tolerance and budget.

Sites with Natural Protection

Some coastal sites are naturally protected by dunes, wetlands, or offshore barriers that reduce wave energy and surge levels. In these cases, the design loads may be significantly lower than what the flood maps suggest. However, relying on natural protection is risky because those features can be eroded or degraded over time. We recommend that if a building is sited behind a dune, the dune should be maintained and the building should still be designed for a scenario where the dune is breached. The cost of adding a few feet of freeboard is usually worth the insurance.

Open Questions and Practical FAQs

Even experienced engineers encounter questions that do not have clear answers. Here are some of the most common open issues we face in coastal structural design.

How do we model 50-year erosion scenarios?

Erosion is difficult to predict because it depends on storm duration, wave direction, and sediment transport. Most codes provide a minimum scour depth, but this is often conservative for some sites and unconservative for others. For critical projects, we recommend a site-specific sediment transport study that models the effects of multiple storms. However, this is expensive and time-consuming. A practical compromise is to use a range of scour depths (e.g., 3, 6, and 9 feet) and design the foundation for the worst case that is still economically feasible. The building can be monitored after storms, and if scour occurs, the foundation can be retrofitted with additional piles or scour protection.

Should we design for survivable flooding or full avoidance?

This is a fundamental question. Full avoidance means elevating the building so that floodwater never reaches the occupied floors. Surivable flooding means allowing some flooding of lower levels, with the expectation that the building will be repaired. For residential buildings, full avoidance is usually preferred because it reduces trauma and cleanup costs. For commercial buildings with large equipment on the ground floor, survivable flooding may be the only option. The decision affects the foundation design: full avoidance requires higher piles and deeper embedment, while survivable flooding allows for a lower elevation but requires waterproofing and drainage systems. We recommend discussing this with the owner early in the design process, as it has major cost implications.

How do we handle utility connections in elevated buildings?

Utility connections are often the weak link in elevated buildings. If the building is raised on piles, the water, sewer, electrical, and gas lines must run up the piles to the first floor. These connections are vulnerable to corrosion, impact, and flooding. We recommend using flexible connections that can accommodate movement of the building relative to the ground. For electrical, use waterproof conduits and locate the panel above the design flood elevation. For sewer, use backflow valves and consider a grinder pump that can lift waste to the elevated line. The cost of these systems is significant, but they are essential for the building to function after a storm.

Summary and Next Experiments

Resilient coastal design requires a shift in mindset from standard practice. The key takeaways from this guide are: (1) understand the site-specific surge, wave, and scour conditions; (2) choose a foundation system that provides both vertical and lateral resistance with redundancy; (3) design a continuous load path that accounts for buoyancy and uplift; (4) avoid anti-patterns like relying solely on sacrificial cladding or ignoring lateral loads; and (5) plan for long-term maintenance and adaptation to sea level rise.

Your next steps

Start by reviewing your current coastal projects against these principles. Identify the most vulnerable components—foundation connections, shear wall anchorage, and utility penetrations. Then, run a scenario analysis for a 50-year storm with sea level rise to see where your design would fail. Finally, discuss with your team the trade-offs between initial cost and long-term resilience. The goal is not to over-design every building, but to make informed decisions that balance risk, cost, and performance. We encourage you to experiment with new materials like fiber-reinforced polymer (FRP) for corrosion resistance, and to explore performance-based design methods that go beyond prescriptive codes. The coast is changing, and our designs must change with it.