Heat, Cold and Weather Risks on Site

What the law actually requires

• The Workplace (Health, Safety and Welfare) Regulations require a reasonable indoor temperature, which HSE says depends on the work activity and the environmental conditions.
• The Construction (Design and Management) Regulations require reasonable temperatures for indoor areas of construction sites. Where the site is outdoors, HSE states you must provide protection from adverse weather, and rest facilities must be kept at an appropriate temperature.
• The Management of Health and Safety at Work Regulations require the risks to be assessed and controls put in place. Temperature is one of them, indoors or out.

HSE also says to consult workers or their representatives on the best ways to cope with high or low temperatures, which is worth remembering: consulting the workforce is the right answer more often than candidates expect.

Weather by weather, what to do

Heat stress and how to spot it

HSE describes heat stress as what happens when the body's way of controlling its internal temperature starts to fail. Air temperature is only one input: work rate, humidity and work clothing all feed into it, which is why a bricklayer in coveralls can be in trouble on a day that feels fine to somebody standing still. The symptoms HSE lists, roughly in order of seriousness:

• an inability to concentrate, muscle cramps, heat rash
• severe thirst, which HSE flags as a late symptom rather than an early warning, then fainting
• heat exhaustion: fatigue, dizziness, nausea, headache, moist skin
• heat stroke: hot dry skin, confusion, convulsions and eventual loss of consciousness, which HSE says can result in death if it is not caught early

Note the direction of travel. Moist skin is heat exhaustion, hot dry skin is heat stroke and a medical emergency. When assessing the risk HSE says to weigh work rate, the working climate, work clothing and types of PPE that stop sweat evaporating, and the age, body type and medical factors of the individual.

Water, and how much of it

Dehydration is the one topic here where HSE publishes figures as plain text, so they are worth learning. Working at a high rate in heat stress conditions, drink around 250ml, about half a pint, every 15 minutes. Where PPE or the task stops you drinking, HSE suggests around 500ml, about a pint, per hour before work starts and the same again during rest periods.

Cool water beats tea, coffee or fizzy drinks, small amounts often beat one big drink, and you should not wait to feel thirsty, because thirst means dehydration has already begun. Heavy sweating loses salt as well as water, so HSE suggests drinks containing the salts the body needs. Drinking water is part of site welfare, covered further in health and welfare.

Working in the cold

The two figures everyone half remembers are 16°C and 13°C. Be precise about where they come from. HSE says the Approved Code of Practice on the Workplace (Health, Safety and Welfare) Regulations suggests the minimum temperature for working indoors should normally be at least 16°C, or 13°C if much of the work involves rigorous physical effort. That is guidance in an ACOP rather than a number written into the Regulations, and it applies indoors. There is no equivalent figure for standing in a field in January.

For outdoor cold work HSE lists appropriate PPE, mobile facilities for warming up, soup or hot drinks, more frequent rest breaks, delaying the work until warmer times of year where that does not compromise safety, and making sure workers can recognise early symptoms such as a cough or body aches.

Wind, work at height and lifting

Wind is the weather that kills people on construction sites, and it does it through height and through plant.

• Roof work. HSE says do not consider going onto any roof in poor conditions such as rain, ice, frost or strong winds, particularly gusting winds, or where the roof is slippery. It adds that winds in excess of 23mph, Force 5, will affect a person's balance.
• MEWPs. High winds can tilt a platform and make it unstable. HSE tells you to set a maximum safe wind speed for operation rather than publishing one, and to inspect the machine before use after severe weather.
• Scaffolds. A construction scaffold is inspected before first use and then every 7 days, and again each time it has been exposed to conditions likely to cause deterioration, which includes adverse weather.
• Tower cranes. After three luffing jib tower cranes collapsed in high winds, HSE issued a safety alert reminding users that a crane left out of service must be in free slew at a safe out of service radius so it can weathervane rather than take the wind broadside.

None of that gives you a single legal wind speed, and an answer that invents one is wrong. The pattern matches the hierarchy of control: avoid the exposure, and where you cannot, plan it within limits somebody competent has set. More of this comes up in working at height and site transport.

Sun exposure is an occupational risk

HSE names construction workers among the outdoor workers whose skin is exposed to more sun than is healthy. A tan is not a sign of health, it is a sign the skin has already been damaged by ultraviolet light. Short term that means reddening, sunburn and blistering. Long term it means leathery, mottled, prematurely aged skin and an increased chance of skin cancer. HSE's advice is short enough to remember: keep your top on, wear a hat with a brim or a flap covering the ears and the back of the neck, stay in the shade at breaks, use a sunscreen of at least SPF30 on exposed skin, drink plenty of water, and see a doctor promptly about any mole or spot that changes shape, size or colour, or that itches or bleeds.

Anyone can be affected. HSE notes that people of all skin colours should take care to avoid eye damage, overheating and dehydration, with particular care for fair or freckled skin, red or fair hair and light eyes, or a large number of moles.

Practise the weather and welfare questions

Weather questions are usually welfare questions wearing a coat: cool drinking water, somewhere warm to take a break, rest facilities at a sensible temperature. Work through the health and welfare questions with explanations, browse every practice topic, or sit a free CSCS practice test to find the gaps. If the day goes wrong and somebody is taken ill from the heat, what happens next is covered in RIDDOR.

Verified August 2026 against hse.gov.uk. The absence of a maximum working temperature, the reasonable temperature duty, the CDM adverse weather duty, the 16°C and 13°C ACOP figures, the heat stress symptoms and controls, the dehydration volumes and the outdoor working lists come from Temperature in the workplace at hse.gov.uk/temperature/employer/, including its What the law says, Heat stress, Cold stress, Dehydration and Outdoor working pages. Sun advice comes from Skin at work: outdoor workers and sun exposure. The 23mph roof work figure and the scaffold inspection intervals come from the construction work at height FAQ, the MEWP wind advice from the construction MEWP page, and the out of service tower crane alert from HSE safety bulletin FOD 2 of 2014. No maximum working temperature and no stop-work wind speed for plant are quoted here, because HSE publishes neither.