UK offices weren’t built for this. Most commercial buildings still in use today were designed decades ago, when a hot summer meant a handful of uncomfortable afternoons rather than sustained periods above 30°C. That’s changed, and it’s now a real factor to plan for in any office fit-out or refurbishment.
For businesses investing in a new workspace, thermal comfort deserves the same attention as layout, lighting, or branding. An office that overheats every summer isn’t just uncomfortable. It affects concentration, decision-making, and how long staff are willing to stay in the building on a warm day.
This is squarely a fit-out and refurbishment issue, not just an M&E one. Glazing choices, ceiling design, material selection, and cooling capacity all get decided during the design and build process. Getting them right from the outset is far cheaper than fixing them once the building is occupied.
Why UK Offices Struggle With Heat
Buildings designed for a temperate, heat-retaining climate don’t cope well when temperatures climb and stay high for days at a time. Add in trends that have become standard in modern workspace design, and the problem compounds:
- Larger areas of glazing for natural light and a more open feel
- Higher desk density in open-plan layouts
- More IT equipment and server capacity generating heat internally
None of these are wrong choices on their own. They just need to be balanced against how the building manages heat, which is where fit-out planning comes in.
According to the Health and Safety Executive, there’s no legal maximum workplace temperature in the UK, but employers have a duty to keep conditions reasonable and to manage risks from thermal discomfort. That puts the responsibility on building design and workplace management to get ahead of the problem, rather than reacting to it once staff raise concerns.
Designing Heat Resilience Into Your Fit-Out
Glazing and Solar Shading
Glazing is usually the biggest single factor in summer overheating. Large windows on south or west-facing elevations let in significant solar gain, particularly in the afternoon.
Worth considering at design stage:
- Solar control film or coated glass on exposed elevations
- External shading such as brise-soleil or fixed awnings, which block heat before it reaches the glass
- Reviewing glazing ratios early, rather than trying to compensate with internal blinds later
Internal blinds help with glare, but they do very little to stop heat once it’s already inside the space.
Ventilation Strategy
Mechanical cooling shouldn’t be doing all the work. A good ventilation strategy reduces reliance on air conditioning and keeps running costs down.
Key elements include:
- Cross-ventilation between opposite-facing windows or vents where the building allows it
- Night purge ventilation, using cooler night air to remove heat before the next working day
- Ceiling void design that allows air to move rather than trapping heat above suspended ceilings
M&E and Cooling Capacity
Cooling systems need to be sized around the building’s actual solar exposure and occupancy, not a generic specification.
This means:
- Zoning cooling so meeting rooms, open-plan desking, and server rooms aren’t competing for the same capacity
- Assessing existing HVAC condition properly during a refurbishment rather than assuming it’s adequate
- Accounting for heat generated by IT equipment, which is frequently underestimated in cooling calculations
Materials and Fabric
The materials used in a fit-out affect how a space handles heat over the course of a day.
Exposed thermal mass, such as concrete soffits, can absorb heat during the day and release it overnight. Lighter, more reflective internal finishes reduce heat absorption compared with dark surfaces. Insulation upgrades carried out during a refurbishment address both winter heat loss and summer heat gain in a single project.
Common Mistakes to Avoid
Treating shading purely as an interior design decision, rather than a performance requirement, is one of the most common issues we see raised in industry guidance. Internal blinds address glare, not heat gain.
Underestimating occupancy density is another. More desks in the same footprint means more heat generated internally, on top of solar gain, and cooling plans need to reflect that.
Server and comms rooms are often placed wherever space allows, with little thought given to ventilation, and end up as the hottest part of the building by mid-afternoon.
Assuming existing HVAC will cope is a costly assumption. Older systems were rarely designed for current occupancy levels or the frequency of hot weather the UK now experiences.
Costs and Timing
Retrofitting solar control film is generally one of the lower-cost interventions and can usually be carried out without disrupting daily operations.
External shading structures cost more to install but tend to outperform internal alternatives and reduce ongoing cooling demand.
The most cost-effective approach is addressing heat resilience as part of a planned fit-out or refurbishment, rather than as a standalone reactive project later. Bundling glazing treatment, ventilation review, and M&E assessment into one phase of work typically costs less and causes less disruption than tackling each element separately after the fact.
Project timelines vary with scope, but building heat resilience into the design stage rarely adds significant time. It’s retrofitting after the building is in use that tends to cause delays.
Key Takeaways
Heat resilience is a design decision, not an afterthought. Glazing, ventilation, M&E sizing, and material choices all get decided during a fit-out, so they should account for summer performance from the start.
Getting this right avoids the scramble every time a heatwave hits, and it protects the comfort and productivity of the people using the space.
Get in Touch
If you’re planning an office fit-out or refurbishment and want practical advice on keeping your space comfortable through the summer months, SJP Interiors can help. Get in touch to discuss your project.
