Draft. These pages were imported from the ARC Technical Criteria document (16 April 2026) and have not yet been reviewed in this format. Several thresholds are still being settled and are flagged on the pages concerned.

ARC Cool Buildings Standard

Thermal comfort and building performance in hot, and hot and humid, climates.

Browse the pages below, or ask a question.

Overview

• Climate and weather - Building performance is normally reported against the 'current climate', but that baseline is itself moving. Performance now has to be assessed against both current and predicted future extreme weather.
• Introduction - The ARC expert group's current understanding of key technical aspects of thermal comfort and wellbeing, and ARC's building performance standard for minimising occupant overheating in hot, and hot and humid, climates.
• Success criteria for building modelling and performance - The ARC Cool Buildings Standard aims for all-year-round thermal comfort in hot and hot-humid climates, principally through passive design, while mitigating dangerous conditions during heatwaves.
• The ARC framework - two Steps and three Zones - The framework supports occupants managing their health and comfort through simple, robust adaptive behaviour, and focuses designers on future-proofing. It consists of two Steps and three Zones.
• The Cool Buildings Programme - The five components of ARC's programme - design strategies, the dynamic adaptive-comfort model, building science resources, prescriptive measures and exemplar buildings.
• What influences thermal comfort - Thermal comfort depends on six factors - four environmental and two personal - plus acclimatisation, expectation and a person's thermal history. Air temperature alone predicts comfort badly.

Patterns

• Designing a heat refuge - The passive measures that keep a heat refuge below its temperature limit when the power is off - orientation, shading, reflective surfaces, heat-shedding roofs, window openings and draughtproofing.
• Leveraging adaptive comfort - the three-zone strategy - The three-zone approach arranges a building's form, functions and detailed layout around its context, the wind and the sun's path, so it can operate passively whenever necessary.
• Step 1 and Step 2 - Step 1 is a naturally ventilated building designed so mechanical cooling can be added later without locking out passive operation. Step 2 is a fully conditioned building that can still run naturally ventilated.
• Zone 1 - mechanically cooled and ventilated - Zone 1 areas must operate energy-efficiently in mechanical cooling and ventilation mode, and in less harsh climates be able to turn the mechanical systems off and work naturally ventilated.
• Zone 2 - the communal heat refuge - A communal heat refuge, large enough to accommodate all building occupants, for use during extreme heatwaves - and which must keep working during power cuts.
• Zone 3 - transient and buffer spaces - Naturally ventilated spaces which, because of their transitory functions, can accommodate higher temperatures than the ARC limits for zones 1 and 2 - and which can be used to shade other rooms.

Reference

• Defining and monitoring heatwaves - How the WMO, the Met Office and the IPCC define a heatwave, the threshold methods in use, who monitors them, and why coverage gaps matter for the global south.
• Measuring thermal comfort - the temperatures - Dry bulb, wet bulb and dew point temperature explained, plus the heat index. These are the measurements the ARC comfort model and its thresholds are built on.
• Physiological adaptation to heat - People adapt to the weather they have recently experienced. ARC prefers the running mean outdoor temperature over a monthly average, because adaptation drops off sharply after about seven days.
• Practical advice during a heatwave - What occupants can actually do when it is dangerously hot - siestas, moving around the building, tepid showers, fans, when to open and close windows, and a solar-backed shelter.
• R&D brief - air conditioning and ventilation for hot humid climates - ARC's technical brief for a prototype air-conditioning unit that balances cooling against dehumidification and supplies fresh air without a large energy penalty.
• Resources - The open dataset and published research the ARC comfort model draws on.
• Success criteria - the temperature thresholds - Zone 1 and 2 spaces should remain below the comfort model's humidity-adjusted thresholds for at least 90% of the time. Separate thresholds apply during heatwave conditions.
• Temperatures of transient spaces during heatwaves - Spaces people need to use for more than an hour each day - kitchens, bathrooms and corridors - should not exceed the human limits for temperature.
• The ARC comfort model - ARC uses a humidity-inclusive adaptive comfort model. More humid climates require more stringent comfort standards, because the body's ability to sweat is diminished in humid air.
• Thermal comfort models - The two models most standards are built on - steady-state heat balance and adaptive comfort - and the factors that feed them, from clothing and activity to humidity and air speed.