From IT Controls to Engineering Resilience: Rethinking Smart Building Cybersecurity

As smart buildings become more connected, cybersecurity is increasingly treated as a standard IT problem, restrict access, encrypt communications, authenticate every device, and monitor continuously for anomalies. These practices are well established in enterprise networks and are often recommended for smart buildings.

However, buildings are not just networks. They are physical systems that control airflow, temperature, lighting, and access to space. When cybersecurity controls are applied without engineering context, they can introduce new risks, not just cyber risk, but operational failure risk. In buildings, the goal of cybersecurity is not only to defeat attackers, but to ensure the building continues to operate safely and predictably when security mechanisms fail.

Why This Matters: A Real Building Scenario

Consider a large, occupied office building with a centralized HVAC system. To improve cybersecurity, encrypted communications and device authentication are added between the building management system (BMS) server and field controllers. Access is tightly restricted, and zero-trust principles are applied so that every connection must be continuously verified.

On paper, the building appears more secure.

Months later, a routine certificate renewal is missed on a subset of HVAC controllers. When the system attempts to reauthenticate, communication fails. Controllers stop responding to commands from the BMS. The issue is not immediately obvious to operators, because no alarms indicate a mechanical fault.

Within hours, occupants begin reporting temperature and ventilation problems. Some zones drift outside acceptable limits. Operators attempt to intervene but find their access restricted by the same security controls designed to protect the system. The building has not been hacked, yet it is no longer operating safely or predictably.

In this scenario, cybersecurity did not fail because of an attacker. It failed because security mechanisms became part of the control system, and when they failed, the building failed with them.

Why Security Controls That Work in IT Can Break Buildings

Many cybersecurity practices assume systems can tolerate delay, interruption, or temporary loss of connectivity. Building control systems often cannot.

Building automation devices commonly remain in service for 15 to 30 years and were not designed for frequent credential changes, encryption overhead, or continuous authentication. Control communications are often deterministic and time-sensitive. Introducing latency, dropped packets, or failed handshakes can disrupt control logic in subtle but serious ways.

In legacy buildings, replacing all equipment to support modern cybersecurity features is rarely feasible. As a result, security controls are often layered onto systems that were never designed to support them, turning cybersecurity into a potential single point of failure.

The Hidden Risk: When Security Controls Fail First

In buildings, cybersecurity failures rarely announce themselves as cyber events. They appear as comfort complaints, airflow problems, access failures, or systems that stop responding. When security controls interfere with operator visibility or control, response time increases and situational awareness degrades.

Zero-trust architectures can be effective when applied to user access and remote management interfaces. However, when applied indiscriminately to operational control paths, they can interrupt communications that must remain continuously available. Encryption can protect data in transit, but when applied to resource-constrained controllers, it can introduce delays or failures that compromise system stability.

In these cases, cybersecurity measures designed to protect the building can unintentionally become a source of operational disruption.

Fail-Safe Thinking Must Apply to Cybersecurity

In traditional building design, critical systems are expected to fail safe. Fire dampers close, valves move to known positions, and equipment enters predictable states when power or communications are lost. Cybersecurity mechanisms should be held to the same standard.

If a cybersecurity control fails, whether due to misconfiguration, expiration, or software fault, it must not cause the building to enter an unsafe or uncontrollable condition. Designing cybersecurity without fail-safe behavior can unintentionally turn protective controls into operational hazards.

Engineering-led cybersecurity requires asking not only how systems are protected, but how they behave when protection mechanisms themselves stop working.

Progress and Limits: A Note on Newer Technologies

Newer technologies such as BACnet/SC represent an important step toward improving security in building automation systems and introduce stronger protections where supported.

However, BACnet/SC is not widely deployed today and is not designed to retrofit decades-old equipment. Most existing buildings will continue to rely on legacy systems for many years. Cybersecurity strategies must therefore work within current operational constraints rather than assuming wholesale replacement of infrastructure.

Engineering-Led Cybersecurity: A Different Objective

Engineering-led cybersecurity starts with a different objective. Instead of focusing solely on preventing unauthorized access, it asks a more fundamental question, how does the building behave when cybersecurity mechanisms fail?

Some security controls will fail, some failures will be silent, and some failures will occur during normal operations rather than attacks. The measure of success is not simply blocked connections or alerts generated, but whether the building remains safe, controllable, and predictable under adverse conditions.

What Engineering-Led Security Looks Like in Practice

For building owners and facilities managers, this shift does not require abandoning cybersecurity best practices, but applying them with operational intent.

An engineering-focused approach adapts cybersecurity principles to the realities of building systems.

Protect access, not real-time control paths. Apply strong authentication and zero-trust concepts to user access and remote management, not deterministic control loops.

Design cybersecurity controls to fail safe. Ensure systems move to known, safe operating states if communications or security mechanisms malfunction.

Preserve operator authority. Operators must be able to regain control during incidents, even when cybersecurity controls fail.

Align segmentation with physical function. Network boundaries should reflect how systems interact operationally, not just how networks are organized.

Test cybersecurity failures like power failures. Cyber incidents should be part of routine operational testing and response planning.

This approach treats cybersecurity as part of system reliability and safety, not as an external overlay.

What Building Owners Should Do Differently

For building owners and facilities managers, engineering-led cybersecurity means shifting how success is defined.

Do not assume IT security controls can be applied unchanged to building systems.

Treat loss of control as a primary cybersecurity risk.

Ask how security mechanisms fail, not just how they protect.

Ensure legacy systems are protected without becoming brittle.

Measure success by safe building behavior, not blocked connections.

These steps help prevent cybersecurity from becoming a new source of building failure.

Moving Forward

Smart buildings will continue to become more connected, and cybersecurity will remain essential. But protecting buildings requires more than importing IT security practices or focusing solely on defeating attackers.

By treating cybersecurity as an engineering discipline, grounded in fail-safe behavior and operational resilience, building owners can reduce risk without compromising reliability. In smart buildings, cybersecurity succeeds not when attacks are blocked, but when the building continues to operate safely, predictably, and under control.