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.

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.

Heatwaves pose serious risks to people's health and wellbeing, and limit their daily lives at work and at home - because in order to manage a heatwave, and even to survive it, reducing heat stress becomes the sole focus.

It is therefore important to ensure that people have access to at least one space at home, at work and in community settings for practical use and refuge during heatwaves. ARC calls this the Heat Refuge.

The Heat Refuge is a cooler, sheltered space which building occupants are able to use for extended periods during heatwaves, and which stays below certain temperature limits even when mains power cuts out. It may be a single space, or a zone including several rooms. It corresponds to Zone 2.

The requirement

Temperature limit

Designers and builders must ensure that during extreme heat events the Heat Refuge remains below 32–35 °C through passive (non-mechanical) design measures.

The source document gives this limit as a range. The exact figure is still being settled by ARC - see success criteria.

Orientation

Minimise the amount of time direct sun heats the walls, roofs, floors and external surroundings.

Typically this involves aligning the longest and largest external faces of the building to face north and south - in hot climates the sun is higher in the sky to the north and/or south during the day - and aligning the narrow, smallest faces to face east and west, where the sun is lower in the sky and more sunlight falls on walls and windows.

Good solar orientation of a building is an extremely effective way to reduce the amount of heat from the sun getting into a building.

Shading to walls and windows

• extending the roof edges to extensively shade walls and windows - and even to shade external ground areas around the building - is highly effective at keeping buildings cool
• adding lean-to or canopy roofs against walls
• shading the tops and sides of windows using features fixed to the walls
• ventilated window shutters, on the outside of the window
• ventilated shading louvres within the window opening
• externally positioned perforated security screens (Mashrabiya).

Reflective surfaces

Brilliant white - the most reflective - or paler colours help reflect the sun's heat away from the building's roof and walls.

This is particularly important where there is no ceiling in the room and occupants are exposed to the radiant heat coming off metal roof sheets. It also works well to reduce heat being radiated onto, and through, plasterboard or concrete ceilings below. Keeping ceilings cooler is important.

Heat-shedding roofs

Heat builds up quickly in enclosed roof spaces. If the hot air cannot escape from the roof space, it transfers its heat to the ceiling materials, making the ceilings hotter. Heat is then radiated from the ceilings onto the occupants below.

Provide ventilation to the roof space at the eaves, allowing cooler air in, and have dedicated areas that let the hot air out of the roof towards the top - also designed to keep the rain out.

Using window openings for air movement

Make sure window openings are large enough to allow a high level of air movement. Ventilated shutters, louvres or venetian blinds can be used to increase or decrease how much air passes through a window, so air movement can be controlled by the occupants.

The important thing is to avoid sizing the openings too small in the first place, and to make sure they are placed on opposing walls of the space, or at least on adjacent walls. Rooms with a single window should be avoided.

This requires windows to be placed carefully, to provide cross-ventilation - ideally openings of equal size on opposing sides of spaces, to allow the free flow of air across the space.

If the space is to be sub-divided with an internal wall, consider making the partition 'perforated' to avoid blocking air movement from the window, thereby improving cooling cross ventilation.

Lowering the window cills provides better cooling, by allowing air to pass across more of the body area of occupants standing, sitting or lying inside.

Treat ceiling openings as experimental

Creating openings in ceilings 'to let hot air rise out of the room' is not generally considered to be very effective in domestic buildings, and may allow more heat into the space than it lets out. Treat this potential passive measure as experimental at this time.

Draughtproofed glazed windows, for when air conditioning is on

Inward-opening casement windows, or glazed bifold patio doors, will be needed for the operation of the Heat Refuge in two modes - natural ventilation mode and air conditioning mode.

In natural ventilation mode the casements are open, to allow for full opening of the window area for effective cross ventilation.

Fitting an insect mesh screen across the window opening is necessary for areas with mosquitoes. This typically reduces airspeed through the window by about 50% - and airspeed is the critical factor for cooling the body.

The glass areas of sliding-type glazed windows typically occupy 50% of the opening area of the window, and their insect mesh areas slow air movement by 50%. So the reduced distribution of cooling breeze across occupants' bodies when using sliding-type glazed windows needs to be considered carefully by designers and builders.

For what occupants themselves can do once a heatwave arrives, see practical advice during a heatwave.

Services in the refuge

• powered fan or fans
• lighting
• power socket or sockets.

If an adequate mains power supply is available, this space should also be fitted with mechanical cooling - but passive measures must be favoured, to anticipate maintaining cool temperatures during power cuts.

The reason for installing air conditioning in the Heat Refuge is that in places where power cuts are anticipated, or even scheduled, occupants can pre-cool a room with the air conditioner and rely on the good design of the space to preserve that coolth for as long as possible during the power cut.

What differs by climate

Hot dry climate with adequately cool nights. A well-shaded room with high thermal mass, cooled at night by natural ventilation via large openings, is important.

Hot humid climate. The room should be provided with additional wall, floor and/or ceiling insulation, to preserve the coolth.

Why power cuts drive the design

Heatwaves often come with power cuts, as power grids struggle to handle the demand of people turning on their air conditioning.

In line with the need to manage this increasing risk, ARC's approach is to design for operational resilience - to safely manage interruptions to energy supplies, typically electricity supply, whilst continuing to provide thermal safety and wellbeing during power outages.

This requires simple and robust 'passive' designs for buildings. The same principle of simplicity and robustness applies to the building services equipment: for example, the use of standardised or locally made and repairable equipment and components, adequate access to local and affordable skills and services, and businesses and authorities building and maintaining suitable and reliable supply chains.

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Source: ARC Technical Criteria - Temperatures in Heat Refuges
Pattern · confidence medium · Imported 2026-08-29, not yet reviewed · next review 2026-11-29
Tags: heat-refuge, passive-design, shading, ventilation, heatwaves, orientation
Citation key: heat-refuge-design