Key takeaways
- Heat is a WHS hazard. Businesses must manage the risk of heat-related illness so far as is reasonably practicable; there is no single temperature at which the law says work must stop.
- The risk depends on air temperature, humidity, sun, air movement, how hard the work is, what workers wear, and how acclimatised they are.
- Roofs, roof spaces, unshaded slabs and enclosed rooms without airflow are among the hottest workplaces on a residential site.
- Controls include scheduling heavy work for cooler times, shade, cool water and rest breaks, lighter PPE and clothing, and gradual acclimatisation for new or returning workers.
- Heat stroke is a medical emergency. Everyone on site should know the signs and what to do.
Spring has arrived, and with it the chance to prepare for something every builder knows is coming: summer heat. On a residential site, a metal roof in January, a roof space under dark tiles, or a slab pour on a still, humid afternoon can push workers to the edge of heat illness. Heat illness ranges from cramps and rashes to heat stroke, which can kill. Planning now, before the first heatwave, means the controls are in place when they are needed.
Heat is a WHS hazard
Under WHS laws, businesses must manage the risk of heat-related illness in the same way as any other risk: identify the hazard, assess the risk, and put controls in place so far as is reasonably practicable. Safe Work Australia’s guidance on working in heat sets out how.
A common misconception is that there is a set temperature at which work must legally stop. WHS law does not set one. Instead, the business must assess the actual risk, which depends on many factors beyond the air temperature, and act accordingly. Some industrial agreements include heat provisions, which builders should check.
What drives the risk
- Air temperature and humidity. High humidity stops sweat evaporating, so the body cannot cool itself effectively.
- Radiant heat. Direct sun, and heat reflected from roofs, slabs and walls.
- Air movement. Still air, in roof spaces or enclosed rooms, increases the risk.
- Work rate. Heavy physical work generates body heat.
- Clothing and PPE. Heavy or impermeable clothing traps heat.
- The worker. Fitness, health, medications, hydration and acclimatisation all matter. New workers and those returning from leave are at higher risk.
The hottest places on a house site
- Metal roofs in full sun, and working at height with no shade.
- Roof spaces and ceiling voids, which can be far hotter than outside.
- Unshaded concrete slabs reflecting heat during pours and finishing.
- Enclosed rooms before windows are installed or airflow is possible.
- Plant cabins without working air conditioning.
The heat plan
A heat plan for a residential site
- 1Watch the forecastCheck temperature and humidity daily in summer and plan the day around it.
- 2Reschedule heavy workRoofing, concrete and heavy lifting early in the day; lighter or shaded work later.
- 3Provide shade and waterShade over rest areas and work areas where practical; cool drinking water close to the work.
- 4Build in breaksMore frequent rest breaks in shade as heat rises; rotate the hottest tasks.
- 5Watch each otherBuddy system, supervisors checking in, and new workers acclimatised gradually.
- 6Know the emergency planFirst aid, cooling and calling for help for anyone showing signs of heat stroke.
Scheduling
The most effective control is timing. Schedule the heaviest and most exposed work, such as roofing, concrete pours and heavy lifting, for early in the day. Move lighter or shaded tasks to the afternoon. On extreme days, consider whether exposed work can be postponed. Programme allowances for heat days are part of realistic pricing in summer.
Shade and air movement
Provide shade over rest areas and, where practical, over work areas, using shade structures, temporary covers or scheduling work to follow the building’s shadow. Fans and ventilation help in enclosed rooms and roof spaces.
Water and rest
Cool drinking water should be available close to where people are working, not just in the site shed. Encourage regular drinking before workers feel thirsty. Increase rest breaks as heat rises, taken in shade, and rotate workers through the hottest tasks.
Clothing and PPE
Lightweight, breathable, long-sleeved clothing, wide-brimmed hats or brim attachments for hard hats, and sunscreen protect against sun and heat. Where heavy PPE is required, such as for asbestos or silica work, plan shorter work periods and more frequent breaks.
Acclimatisation
The body adapts to heat over a period of days. New workers, apprentices starting in summer, and workers returning from leave or illness need to build up gradually, with lighter workloads and more frequent breaks at first. This is one of the most overlooked controls.
Roof spaces are the danger zone. The inside of a roof space on a summer afternoon can be far hotter than the outside air, with no air movement. Schedule roof space work, such as electrical, insulation and air conditioning installation, for early mornings in summer, limit time spent inside, and never let anyone work in a roof space alone in the heat.
Recognising heat illness
Heat illness: signs and what to do
| Condition | Signs | Action |
|---|---|---|
| Heat rash and cramps | Itchy rash, painful muscle cramps | Rest in shade, drink water, cool down |
| Heat exhaustion | Heavy sweating, weakness, dizziness, nausea, headache, pale skin | Stop work, move to shade, cool down, drink water, seek medical advice if not improving |
| Heat stroke | Confusion, slurred speech, collapse, hot skin, may stop sweating, seizures | Emergency: call 000, cool the person immediately, first aid |
Source: General first aid guidance; follow your first aider’s training and emergency services’ advice.
Heat stroke is a medical emergency. A worker who becomes confused, slurs their speech, collapses, or has hot skin and may have stopped sweating needs immediate help: call emergency services, move them to shade, and start cooling them while waiting. Everyone on site should know these signs, and first aiders should know the treatment.
The buddy system
People affected by heat often do not recognise it in themselves, because confusion is one of the symptoms. Pairing workers to watch each other, and supervisors checking in regularly on hot days, catches problems early. This is particularly important for workers on their own, on roofs, or in roof spaces.
Heat and other hazards
Heat makes other hazards worse. Fatigue and dehydration slow reactions and affect judgement, increasing the risk of falls and plant incidents. Sweaty hands affect grip on tools and ladders. Heat also contributes to irritability and conflict on site. A heat plan protects against more than heat illness.
Heat and concrete, render and materials
Heat affects materials as well as people. Concrete sets faster and loses moisture quickly in hot, windy weather, which can cause plastic shrinkage cracking and weak surfaces if it is not protected and cured properly. Renders, adhesives, sealants and membranes have maximum application temperatures and faster working times in heat. Scheduling pours and finishing work early in the day protects both the crew and the quality of the work, which is another reason heat planning belongs in the programme.
Heat and the programme
Summer heat days are as predictable as wet days. Builders who allow for them in summer programmes and pricing, with earlier starts, shorter exposed work periods and some lost afternoons, are far better placed than those who promise clients a winter-speed programme in January and then push crews through the heat to meet it. If a job falls behind in summer, the answer is resourcing and resequencing, not longer hours on the roof in the middle of the day.
Subcontractors and the heat plan
Most workers on a house site work for subcontractors, who have their own duties to their workers. The builder’s role as principal contractor is to coordinate: share the site heat plan, provide the site-wide controls such as shade at rest areas and water, and make sure subcontractors’ work methods account for heat. Roofers, concreters and bricklayers, who do the most exposed work, should be part of the planning conversation before summer.
Mental health and heat
Long, hot days wear people down. Heat contributes to fatigue, frustration and conflict, and it can add to the pressure on workers already under stress. Keeping an eye on how people are coping, not just physically, is part of looking after a crew in summer.
Consultation and records
Consult workers about the heat plan: they know which tasks and places are hottest. Include heat in the site induction and hold a toolbox talk at the start of summer and before forecast heatwaves. Record the plan, the talks and any heat-related incidents. If a worker suffers heat illness, notify the regulator if it meets the threshold for a notifiable incident, and review the plan.
Setting up the site for summer
Much of a heat plan is set up once, at the start of the season or the start of the job. A shaded rest area with seating, close to where people work. A water supply that stays cool, such as insulated containers refilled through the day, rather than a tap in the sun. Sun protection supplies on site: sunscreen, brim attachments, cooling towels. First aid supplies that include cooling equipment and a clear procedure for heat emergencies. A thermometer or a phone app that tracks heat and humidity. A noticeboard entry with the heat plan and the signs of heat illness. None of this is expensive, and all of it is easier to organise in September than in the middle of a January heatwave.
Workers most at risk
Some workers are more vulnerable to heat than others: those who are new to outdoor work or returning from leave, older workers, workers with some medical conditions or taking certain medications, and anyone who is unwell, dehydrated or has been drinking alcohol the night before. Workers do not always volunteer this information, which is why a culture where people can say “I’m not coping in this heat” without being judged is an important control in its own right.
A worked example: the January roof
A builder has a metal roof to install on a two-storey house in mid-January. The forecast shows several days of heat and high humidity. The builder and the roofer agree to start at first light, finish the exposed sheeting by late morning, and use the afternoons for work in the shade of the house or not at all on the hottest day. Water is kept on the scaffold platform, a shade sail is rigged over the scaffold landing, and the crew takes a break every hour. A new labourer who has just started is kept on ground-level tasks for the first week. The roof goes on two days later than it would have in cooler weather, and nobody ends up in hospital.
The bottom line
Heat is predictable, and so are the controls: plan the day around the forecast, do the heaviest work early, provide shade and cool water, build in rest breaks, acclimatise new workers, watch each other, and know the signs of heat stroke. Get the heat plan in place in spring, before the first heatwave, and summer becomes a scheduling problem rather than a medical one.
Questions builders ask
Is there a temperature at which work must stop on a building site?
WHS law does not set a single temperature. Businesses must assess and manage the risk of heat illness based on the actual conditions and work. Some industrial agreements include heat provisions.
What are the signs of heat stroke?
Confusion, slurred speech, collapse, hot skin, possibly stopped sweating and seizures. Heat stroke is a medical emergency: call 000, move the person to shade and start cooling them.
How can builders reduce heat risk?
Schedule heavy and exposed work for cooler times, provide shade and cool water, increase rest breaks, use light breathable clothing, acclimatise new workers, and use a buddy system.
Why are roof spaces dangerous in summer?
They can be far hotter than outside air with little air movement. Work in roof spaces should be scheduled for cooler times, limited in duration and never done alone in the heat.
What is acclimatisation?
The body’s gradual adaptation to heat over a period of days. New workers and those returning from leave need lighter workloads and more breaks at first.
Sources
- Working in heat · Safe Work Australia
- Working outside · Safe Work Australia
Published 1 September 2026. General information for builders, not legal, financial or engineering advice for a specific job. Check current requirements with the relevant regulator or standard before relying on them.
