Heat resilience in commercial buildings: beyond comfort cooling

Commercial buildings are increasingly being tested by hotter summers, warmer nights and more intense heatwaves.

June 2026 was England’s warmest June on record, while the UK and Wales recorded their second warmest June in a climate series dating back to 1884. The Met Office also highlighted unusually warm overnight temperatures, with frequent “tropical nights” contributing to record June minimum temperatures across the UK, England and Wales.

For building owners, occupiers and project teams, this matters because heat resilience is not simply a question of adding more comfort cooling. That may be part of the answer, but it is rarely the whole answer.

A commercial building can have cooling installed and still perform badly in hot weather. Poor zoning, weak controls, excessive solar gain, undersized ventilation, failing condensers, poor maintenance, lack of night purge, heat gains from IT rooms and unsuitable operating assumptions can all undermine summer performance.

The practical question is no longer “does the building have air conditioning?”

The better question is: “can the building maintain safe, usable and commercially acceptable conditions during hotter and longer summer periods?”

Why overheating is now a commercial property issue

Overheating used to be discussed mainly in housing, schools and care settings. That has changed.

For offices, retail, healthcare, education and mixed-use commercial buildings, overheating can affect:

• occupier comfort

• productivity

• complaints and tenant satisfaction

• refrigeration and process loads

• plant reliability

• energy costs

• lease negotiations

• refurbishment priorities

• business continuity

A warm reception area is annoying. A failing comms room, overheated retail unit or unworkable office floor is a commercial problem.

CIBSE recommends that overheating risk and mitigation options are assessed in new designs and major refurbishments, alongside energy performance, occupant safety, comfort, health and wellbeing.

That is the right approach. Heat resilience should be part of project strategy, not a late design query when the landlord or tenant asks whether the existing system will cope.

More cooling is not always the right first move

It is tempting to respond to overheating by adding more cooling capacity. Sometimes that is necessary. Existing systems may be undersized, life expired or no longer suitable for changed occupancy.

But increasing cooling without understanding the building can create other problems:

• higher electrical demand

• more roof plant congestion

• planning and acoustic constraints

• refrigerant risk

• higher running costs

• poor part-load performance

• plant rejection heat issues

• coordination problems with existing ventilation and controls

In many buildings, the first gains may come from simpler interventions: controls optimisation, cleaning coils and filters, checking refrigerant charge, adjusting setpoints, recommissioning dampers, improving zoning, adding solar control, improving insulation to heat gains, or reviewing operating hours.

The correct answer depends on the building.

What should be reviewed?

A practical heat resilience review should cover the building, the systems and the way the building is actually used.

Building fabric and solar gain

Glazing ratio, orientation, shading, blinds, roof construction and exposed façades all affect summer heat gains. South and west-facing zones are often the first to show issues.

Solar control can be more effective than adding cooling to fight avoidable heat gain all summer.

Ventilation strategy

Ventilation can either help or make matters worse, depending on outdoor conditions, controls and building type.

Project teams should check whether the building has natural ventilation, mechanical ventilation, mixed-mode operation, night purge, heat recovery bypass and suitable controls.

Cooling capacity and resilience

Cooling capacity needs to be assessed against current and future use, not only original design assumptions.

Occupancy may have changed. IT loads may have increased. Retail units may have higher equipment loads. Offices may have been subdivided. Meeting rooms may be used more intensively than designed.

Controls and zoning

Many overheating complaints are control problems wearing a mechanical disguise.

Poor sensor locations, locked controllers, conflicting landlord and tenant controls, failed actuators, limited zoning and badly commissioned BMS strategies can all result in poor comfort even where plant capacity exists.

Critical spaces

Heat resilience is not only about open-plan office areas.

Comms rooms, server rooms, electrical switchrooms, lifts, reception areas, retail refrigeration zones, treatment rooms and high-occupancy meeting spaces may need separate review.

Maintenance and condition

Dirty coils, blocked filters, failed valves, poor refrigerant charge, flat belts, corroded condensers and tired controls all reduce real performance.

A design calculation is useful. A plantroom inspection is often more useful.

Retrofit and refurbishment projects need future weather thinking

UKGBC’s climate resilience work identifies overheating as one of the key climate hazards affecting the built environment, alongside flooding, drought, wildfire and storms.

For commercial refurbishments, this means summer design should be treated properly from the start.

That does not mean oversizing everything. It means using sensible future weather assumptions, assessing passive measures, testing options and making sure the MEP design is coordinated with the façade, fit-out, occupancy and landlord requirements.

Good retrofit decisions should reduce energy use and improve resilience. Poor decisions can do the opposite.

The commercial case for heat resilience

For landlords, heat resilience protects asset quality. Buildings that cannot provide reasonable summer comfort may become harder to let, particularly where tenants are comparing refurbished space.

For occupiers, it protects operations. Staff comfort, customer experience, IT resilience and operating costs all matter.

For managing agents, it reduces complaints and reactive call-outs during hot weather. Nobody wants to discover a condenser failure during the hottest week of the year. That is not a maintenance strategy. It is a stress test with invoices attached.

For project managers, early review reduces late-stage design change. If roof plant, electrical capacity, acoustic constraints or planning issues are only discovered late, options narrow quickly.

What clients should do now

Commercial building owners and occupiers should consider a targeted heat resilience review where:

• the building has known summer comfort complaints

• cooling plant is over 10 to 15 years old

• occupancy or tenant use has changed

• a refurbishment or fit-out is planned

• there are critical rooms with local cooling

• the asset is being prepared for sale, refinance or letting

• previous overheating issues have been treated as isolated maintenance problems

The review does not need to be overcomplicated. A sensible starting point is a building survey, plant condition review, controls review, occupancy check, maintenance record review and high-level cooling and ventilation assessment.

Where required, this can then feed into dynamic thermal modelling, option studies, plant replacement planning or refurbishment design.

How J-WEBS can help

J-WEBS supports landlords, occupiers, managing agents and project teams with building services surveys, MEP technical due diligence, overheating reviews, cooling resilience assessments, decarbonisation studies, EPC improvement planning and refurbishment design.

Heat resilience is now part of building performance. The best approach is practical: understand the asset, identify the weak points, and plan improvements that work technically, commercially and operationally.

If your building struggled during recent hot weather, now is the right time to review it. Waiting until the next heatwave tends to produce the most expensive version of the answer.