The UK is in the grip of an exceptional heatwave. The Met Office has issued Amber Extreme Heat Warnings stretching from Monday through Thursday this week, with temperatures widely forecast to exceed 35°C across southern and eastern England, and real potential to challenge the current UK June temperature record of 35.6°C, set back in 1957. Dew points are forecast around 22°C mid-week, making this not just hot, but oppressively humid and a combination that creates serious challenges for building managers, facilities teams, and the occupants they look after.
For most UK buildings, this kind of sustained thermal event is precisely the scenario their climate control systems were never designed for. And without real-time visibility into what’s happening inside those buildings, facilities managers are flying blind.
The Problem with Heat and Humidity Together
Temperature is only half the story. Humidity also has an enormous influence on how occupants experience thermal conditions, and on the health of the building itself.
During a heatwave, outdoor humidity builds alongside rising temperatures. That warm, moisture-laden air finds its way indoors, and without active monitoring, conditions can deteriorate quickly without anyone noticing until it’s too late.
High indoor humidity causes a room to feel thick and uncomfortable, suppressing energy levels and concentration. It can trigger headaches, exacerbate respiratory conditions like asthma, and slow the dispersal of odours. Left unmanaged, elevated humidity also creates the conditions for condensation, mould growth, and long-term structural and health risks. Server rooms and IT equipment rooms face particular risk as electronics are sensitive to both heat and moisture, and a combination of the two can cause irreversible damage.
Equally, HVAC systems working harder in hot weather can inadvertently strip too much moisture from the air. Overly dry conditions carry their own problems: itchy skin, dry eyes, throat irritation, and increased susceptibility to airborne infections.
The ideal indoor relative humidity sits broadly between 40% and 60% RH. Monitoring both temperature and humidity together gives building managers a far more accurate and actionable picture of conditions than temperature data alone.
Practical Applications During a Heatwave
HVAC Optimisation
The most immediate application during hot weather is demand-driven HVAC control. Rather than operating heating and cooling systems on fixed schedules or building-wide setpoints, live temperature and humidity data from individual rooms and zones allows systems to respond precisely to actual conditions. A south-facing meeting room that heats rapidly through the afternoon receives additional cooling resource. A north-facing office that stays cooler doesn’t. The result is both better occupant comfort and more efficient energy use — particularly important when cooling loads are at their peak.
Preventing ‘Sick Building Syndrome’
When indoor environments combine warmth and high humidity, occupants can experience the symptoms collectively described as sick building syndrome: headaches, dizziness, fatigue, and general discomfort. Continuous monitoring allows facilities teams to identify and respond to these conditions before they affect productivity or wellbeing, rather than reacting to complaints after the fact.
IT and Equipment Room Monitoring
Server rooms, comms rooms, and other equipment-dense spaces are at elevated risk during a heatwave. These spaces generate significant heat loads, and cooling system failures during peak outdoor temperatures can lead to rapid temperature escalation. Pressac sensors deployed in these environments — including within server cabinets — provide live alerting if conditions breach defined thresholds, giving IT and facilities teams time to intervene before equipment is damaged.
Legionella and Water Temperature Compliance
Extended hot weather raises ambient temperatures throughout a building, including plant rooms and areas where water is stored or distributed. Where water temperatures rise above safe thresholds, the risk of Legionella bacteria growth increases. Temperature monitoring in these areas forms part of a robust compliance and risk management framework.
Baseline Data for Post-Event Analysis
Beyond immediate response, the data collected during an extreme weather event is genuinely valuable for longer-term building performance analysis. Understanding how quickly different spaces heat up, which areas are most vulnerable, and how effective cooling interventions are provides the evidence base for infrastructure investment decisions whether that’s additional shading, improved insulation, or upgraded HVAC capacity.
The Bigger Picture: Climate and UK Buildings
The current heatwave is not an isolated event. The frequency and intensity of heatwaves has increased worldwide, and the UK is no exception. Climate projections consistently point to summers becoming hotter and drier, with more frequent extreme heat events. The UK’s existing building stock largely designed for a cool, temperate climate is poorly adapted to this reality. Many commercial buildings lack mechanical cooling entirely, or have cooling systems designed for typical summer conditions rather than the kind of sustained heat we are experiencing this week.
Wireless sensor monitoring doesn’t solve the structural challenge of poorly insulated or poorly ventilated buildings, but it provides the real-time intelligence that makes every other intervention more effective. Knowing where the problems are, how severe they are, and how quickly they are developing is the prerequisite for any meaningful response.
For facilities and building management professionals looking to build resilience ahead of next summer, deploying comprehensive temperature and humidity monitoring is a logical and cost-effective starting point.
