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Why AECB targets matter The AECB performance standard provides one of the clearest and most practical frameworks for UK residential design. It sets realistic limits for glazing ratios, shading, summer comfort metrics, fabric U-values, airtightness and ventilation, while remaining aligned with typical UK budgets. For many clients, the assumption is that tackling overheating requires cooling. In reality, most projects meet summer comfort targets simply by aligning with AECB benchmarks. This fabric-fi rst approach also supports wider policy goals, from retrofi t incentives to the transition away from gas and long term reductions in operational energy use. Across Victorian terraces, post-war
heat gains. In these situations, we often combine external blinds or shutters with louvred pergolas, carefully placed deciduous planting or, in some cases, a deliberate reduction in glazing area without sacrifi cing spatial quality.
North-facing spaces are often assumed
to be ‘safe,’ leading to unnecessarily large glazing areas. Without insulation continuity and airtight detailing, however, they leak heat in winter and admit diffuse gains in summer. Good fabric performance matters here just as much as on sunnier elevations. None of these strategies is inherently expensive. What becomes costly is designing a glass box fi rst and attempting to fi x it later with mechanical cooling. The quiet power of insulation, airtightness and continuity, a persistent misconception is that insulation increases overheating. Insulation only traps heat if solar and internal gains are poorly controlled. A well insulated, airtight home with effective shading remains cooler for longer because heat transfer from outside is slowed, cool night time air is retained within the fabric, and hot external air is prevented from leaking in. In EnerPHit and AECB-aligned retrofi ts, we consistently observe lower daytime peaks, more stable overnight temperatures and a dramatically reduced reliance on fans or active cooling. When insulation and airtightness are paired with MVHR, summer comfort improves again. MVHR does not cool a home, but it allows controlled night time ventilation without opening windows on noisy or polluted streets, helping homes shed heat passively without compromising
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security or air quality. Summer comfort emerges from the relationship between envelope performance and ventilation strategy, not from a piece of technology.
Shading & ventilation If there is one habit UK designers and homeowners should adopt, it is this: design shading before designing glazing. External shading reduces solar gain by orders of magnitude more than internal blinds, which simply trap heat on the wrong side of the glass. Yet shading is still widely seen as optional or unnecessary in our climate. In practice, shading alone often reduces peak summer temperatures by 1.5-3°C. When combined with night time purge ventilation, reductions of 4°C or more are possible, often eliminating a need for active cooling. Deep timber reveals, orientation specifi c steel fi ns, overhangs sized through solar modelling, and integrated external blinds can become architectural assets rather than compromises.
UK homes still rely heavily on opening windows for summer comfort. In dense urban areas, this approach often fails due to noise, pollution, insects, and security. The most successful projects combine multiple passive strategies: cross ventilation where the plan allows, stack ventilation using stairwells, secure night time purge routes and MVHR systems with summer bypass. High-level openings such as roofl ights or clerestories are particularly effective. Each litre of warm air leaving at the top of the house draws cooler evening air in at lower levels, delivering comfort gains disproportionate to their cost.
homes, mews houses and 1930s semis, the same lessons repeat. Glazing itself is rarely the problem; poorly designed glazing is. Shading and night ventilation consistently outperform smart thermostats. Fabric- fi rst approaches deliver comfort in both summer and winter, while internal heat gains from appliances and lighting are often underestimated. Most importantly, overheating risk must be modelled before planning, not discovered after construction. In one EnerPHit mews retrofi t, overheating hours were reduced from 12% to under 1% through shading, airtightness, MVHR with summer bypass and secure night time purge paths. Generous glazing remained – comfort and daylight are not mutually exclusive.
Cooler thinking for a hotter future We are moving towards a climate where homes must remain comfortable at external temperatures of 34-36°C, not the 28-30°C peaks of recent decades. Mechanical cooling will become more common, but it should remain a last resort, not a starting point. The UK’s best chance lies in homes that keep heat out, dump heat at night, use airtightness and shading intelligently, and rely on simple physical principles rather than complex systems. Fabric-fi rst is not a slogan; it is a survival strategy for a warming climate. Architects, clients and contractors who embrace it now will create cooler, healthier and more resilient homes – and avoid costly retrofi ts in the years ahead.
Sean Ronnie Hill is an architect & Passivhaus designer
ADF JANUARY 2026
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