If your office Wi-Fi drops, it’s annoying.
If your BMS drops, your building stops breathing.
- No heating.
- No cooling.
- No lifts.
- No access control.
- Possibly no revenue.
Smart buildings don’t fail because the chiller breaks.
They fail because the network underneath it wasn’t designed to cope when something inevitably goes wrong.
This is where resilience stops being a buzzword and starts being an engineering discipline.
Let’s break it down.
1. Resilience Means Designing for Failure
Every component will fail at some point.
- Switches die.
- Power supplies trip.
- Fibre gets cut.
- Firmware crashes.
The question isn’t if.
It’s whether your architecture notices.
The average cost of data centre downtime is over $9,000 per minute according to the Uptime Institute. Even if your building isn’t a data centre, the principle is the same. Downtime is expensive. Operationally and reputationally.
Resilient OT networks assume failure.
That means:
- Fibre rings with automatic rerouting
- Dual power supplies and UPS-backed switching
- High availability firewalls
- Redundant core and distribution layers
- Controller failover where supported
The goal is simple:
Failure should not equal outage.
If someone digs through a fibre, traffic should reroute.
If a PSU dies, no one should notice.
If a controller crashes, services should continue.
Resilience isn’t about perfection.
It’s about continuity.
2. Security: Closing the Back Door
Many building protocols were never designed for hostile environments.
BACnet.
Modbus.
KNX.
They assumed trust.
No encryption.
No authentication.
Flat networks.
That design made sense 30 years ago. It doesn’t now.
According to a RICS survey reported by ITPro, 27 percent of UK buildings experienced a cyber attack in the previous 12 months. That’s not theoretical risk. That’s active exposure.
The Johnson Controls ransomware incident in 2023 reportedly resulted in 27TB of data theft and approximately $27 million in impact. That wasn’t a small integrator. That was a global building technology provider.
OT security now needs to look like IT security:
- Network segmentation between systems
- Secure remote access via VPN or jump host
- Identity-based access controls
- Logging and monitoring
- Regular patching and lifecycle planning
Zero Trust is not just an IT concept. It applies to plant rooms too.
If your BMS is reachable from anywhere without strict controls, you haven’t built a smart building. You’ve built an entry point.
3. Visibility: You Can’t Protect What You Can’t See
Ask a facilities team how many devices are on their OT network.
Most don’t know.
That’s not a criticism. It’s a visibility gap.
Asset discovery and monitoring are foundational to resilience.
You need to know:
- What devices exist
- Where they sit
- What firmware they run
- What traffic patterns are normal
Without that baseline, you can’t detect anomalies.
Visibility also drives optimisation.
Buildings account for around 40 percent of global energy consumption. Smart control strategies and AI-driven optimisation have demonstrated measurable reductions in HVAC energy usage. Real-world case studies have shown savings in the range of 15 to 30 percent depending on implementation.
Monitoring allows you to move from reactive to predictive:
- Detect a failing drive before it trips
- Identify bandwidth saturation before it impacts control traffic
- Spot rogue devices before they become incidents
Unified dashboards that bring IT and OT telemetry together are no longer optional.
If your chiller alarm and your switch port error live in different worlds, you’re missing context.
4. Bridging Legacy and Modern Systems
Here’s the uncomfortable truth:
Most smart buildings are not greenfield.
They’re layered.
Serial Modbus on RS-485.
BACnet MSTP loops.
Vendor-specific gateways from the early 2000s.
And on top of that, we’re trying to deploy:
- Cloud dashboards
- AI optimisation
- Digital twins
- ESG reporting platforms
You cannot rip everything out. That introduces more risk than it removes.
Instead, you bridge.
- Protocol gateways translating legacy traffic to IP
- Secure segmentation around older systems
- Gradual migration to BACnet/IP, MQTT, or OPC UA
- Structured lifecycle planning for phased upgrades
Legacy is not the enemy.
Unmanaged legacy is.
The smart approach is coexistence with control.
5. Turning Complexity into a Repeatable Model
Every building is different.
That’s true architecturally.
It doesn’t have to be true network-wise.
Too many projects reinvent the wheel.
New VLAN plan.
New firewall policy structure.
New topology.
New naming convention.
That’s how technical debt creeps in.
Instead, build reference architectures:
- Defined OT segmentation model
- Standardised core and distribution topology
- Agreed remote access pattern
- Predefined monitoring baseline
- Tested failover procedures
Then repeat it.
Consistency improves resilience.
It also improves security, supportability, and scalability.
And it forces collaboration.
OT engineers.
IT security.
Facilities teams.
Integrators.
If those groups aren’t aligned at design stage, you’re building silos that will break under pressure.
6. This Isn’t Just Tech. It’s Transformation.
Smart buildings are often sold on dashboards and digital experiences.
The real value is trust.
Trust that:
- The building won’t go dark during a firmware update
- The HVAC won’t fail during peak occupancy
- The access system won’t lock everyone out
- The energy platform won’t be compromised
Smart building technologies can reduce energy use significantly when implemented properly. Industry data suggests reductions in the region of 20 percent are achievable through intelligent optimisation and control strategies.
That impacts:
- Operating cost
- Carbon reporting
- ESG compliance
- Tenant experience
But none of it works without a resilient, secure, visible network underneath.
The network is not a utility bolt-on.
It is the foundation.
The Blueprint
If you’re building or modernising a smart environment, focus on five principles:
- Design for failure, not perfection
- Segment and secure legacy systems
- Build full visibility into OT networks
- Bridge old and new technologies safely
- Standardise and repeat your architecture
Resilience isn’t about stopping things breaking.
It’s about making sure no one notices when they do.
And that’s how smart networks power truly smart buildings.