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Overheating is quickly becoming one of the biggest performance risks in new homes, especially in high rise developments and dense urban areas like Central London. As buildings become more airtight and energy-efficient, the same design features that are intended to reduce emissions are making it harder to maintain comfortable indoor temperatures.

This growing tension between overheating risk and energy performance highlights a deeper issue: the industry is still designing for compliance, not for comfort. Building regulations focus on the minimum standards, but these don’t reflect the real-world experience of the people who live in these spaces.

We’re here to unpack the cooling options available in today’s market, examine how each option interacts with energy calculations, and explain why prioritising thermal comfort isn’t just about wellbeing, but is also about future-proofing developments against regulation changes, climate pressures and market expectations.

Meeting the Energy Hierarchy

Before introducing cooling strategies, it’s essential to ensure that all reasonable passive measures have been considered. This is not just good design practice, it is a regulatory requirement under Approved Document O.

According to Approved Document O, buildings should be constructed to meet thermal performance goals ‘as far as reasonably practicable’. These include strategies like window installation (preferably with cross-ventilation), external louvres, and mechanical ventilation systems. Active cooling should only be introduced when these approaches are insufficient.

This principle aligns with the Energy Hierarchy, which prioritises:

1. Reducing the need for energy

2. Using energy efficiently (e.g. high performance ventilation systems)

3. Supplying energy from low-carbon sources

4. Using conventional energy efficiently (which may include cooling systems)

This approach ensures that developments meet compliance by treating cooling as a last resort, not a shortcut.

Overview of Different Cooling Options

Enhanced Mechanical Ventilation with Tempered Air (peak lopping).

This system makes use of the existing mechanical ventilation system (MVHR) and tempers the incoming air before it is supplied into the space. In many cases, it can provide sufficient cooling to effectively mitigate overheating during the summer months, even in locations represented by the most extreme weather files.

An additional unit is installed on top of the standard MVHR system, so while spatial allowances need to be made, it requires no additional ductwork or pipework.

Active Cooling Through Standalone Air Conditioning Units (wall mounted, within the ceiling void or floor standing).

These units provide cooling independently of the ventilation system by recirculating air after cooling it down. They are more powerful than ventilation-based solutions and can deliver significantly greater cooling capacity. However, they come with higher costs, require more space, and may have a visual or spatial impact. Installation and ongoing maintenance are also required. Despite this, they offer the most robust solution for thermal comfort, effectively mitigating overheating and helping to future-proof the development.

Active Cooling Via the Existing Underfloor Heating System Pipework

Certain air or ground source heat pumps can operate in reverse, using the existing underfloor pipework to provide cooling instead of heating. This approach can deliver sufficient cooling to meet standard requirements without the need for additional equipment or installation.

However, if this is not correctly designed, there is a risk of condensation, and cooling the floor can sometimes result in an unpleasant feeling underfoot. That said, the system takes advantage of the floor’s thermal mass, allowing the cold to be stored efficiently, helping to maintain thermal comfort for longer even after the system has shut down.

Comfort Vs Compliance

Current methodologies, such as CIBSE’s TM59, represent minimum advisory thresholds rather than true indications of thermal comfort. These standards are expected to evolve in the coming years to align with the UK’s Net Zero objectives.

To keep pace, developments need future-proof solutions that go beyond simply passing assessments. Introducing a standardised index for the perception of cooling within thermal comfort would help simplify the process and provide a more accurate indication of effective overheating mitigation.

Ultimately, comfort isn’t just about avoiding overheating during peak summer days; it’s about ensuring daily usability, liveability, and wellbeing.

Why the Industry is Falling Behind

Despite growing awareness of overheating risks, thermal comfort is still too often overlooked in the early design stages. Disconnected design teams, tight planning deadlines, and a focus on meeting baseline compliance means that the emphasis falls on compliance rather than occupant comfort.

Cooling strategies are frequently introduced too late in the process or selected based on upfront cost rather than long-term performance and occupant wellbeing. This limits the effectiveness of solutions and can lead to costly retrofits or underperforming buildings.

Adding to the challenge, current assessment methodologies - such as TM59 - have yet to fully align with the UK’s Net Zero targets. This means that projects that are focusing on compliance today may not align with upcoming expectations in both energy performance and occupant comfort.

To stay ahead, the industry needs to shift from a compliance-led mindset to a comfort-led design approach that considers thermal performance from the outset.

Why Comfort Matters for Clients

Thermal comfort isn’t just a design consideration; it is also a strategic advantage. As temperatures rise, the ability to deliver comfortable living environments is key for developers and building owners for many reasons.

Marketability

Comfortable homes are more attractive to buyers and renters, especially in a market where overheating is a growing concern.

Reduce Complaints and Callbacks

Buildings that maintain good thermal comfort will lead to fewer occupant complaints, reduced maintenance issues, and higher levels of satisfaction.

Futureproofing

Aligning with Net Zero and anticipated regulatory changes early on puts developments ahead of the curve and helps avoid costly retrofits.

BREEAM and Green Performance

Thermal comfort is becoming increasingly important in environmental assessments like BREEAM, making it a factor in both sustainability credentials and investor interest.

Comfort isn’t just about occupant wellbeing; it’s a measurable benefit that adds long-term value to any project.

How We Can Help

At AES, we take a proactive and integrated approach to mitigating overheating and enhancing thermal comfort – treating it as a core design consideration, not an afterthought.

We work with design teams from the earliest stages to embed effective overheating strategies into the architectural and M&E design process. Our advice balances the need for occupant comfort with energy performance, always aligning with the principles of the energy hierarchy.

We help clients choose the right cooling solution at the right time, ensuring systems are not only technically suitable, but also align with project goals, budget, and long-term performance expectations.

For us, thermal comfort is a marketable asset, and not just a compliance tick-box. We stay ahead of industry changes, policy updates, and regulatory shifts to ensure our clients are future proofing their developments, not playing catch-up.

Whether you're looking to enhance market appeal, meet sustainability targets, or reduce long-term risk, we deliver tailored, forward-thinking solutions that put comfort at the centre of your strategy.