Working in Heat on Construction Sites: Staying Safe

There's no maximum working temperature in UK law. HSE says so plainly. That doesn't mean anything goes. Employers still have to assess heat risks, provide drinking water and protect outdoor workers from the weather where they reasonably can. On a building site, heat and sun build up fast. Heavy work, PPE and little shade can turn a hot afternoon into heatstroke. Here's how to plan for it, and what to do when someone goes down.

Is there a maximum temperature for working on site?

No. HSE says there's no law for a maximum working temperature, or for when it's too hot to work, because every workplace is different.

The Construction (Design and Management) Regulations 2015 still set some rules for sites:

• Indoor site areas must be kept at a reasonable temperature during working hours.
• Outdoor sites must give protection from adverse weather where it's needed for health or safety, as far as reasonably practicable.
• Every site must have an adequate supply of drinking water in easy-to-reach places.

The UK Health Security Agency and the Met Office run heat-health alerts. The core season runs from 1 June to 30 September, and anyone can sign up for the weather-health alerts by email. Signing up gives a site manager warning to change the plan.

Why heat hits harder on a building site

Heat stress happens when your body can't keep its core temperature down. HSE lists four things that drive it. They're how hard you're working, the air temperature and humidity, what you're wearing, and your own age, build and health.

A site stacks all four. Labouring, carrying and digging push your work rate up. Hard hats, hi-vis and overalls hold heat in. Coveralls and respirators for jobs like asbestos removal can stop sweat doing its job at all. Many sites have little shade, and roof and scaffold work often has none.

HSE names construction workers among the outdoor workers most at risk from the sun too. Sunburn is the short-term damage. Skin cancer is the long-term one.

How to plan site work for hot weather

Most of the fix is planning. HSE's guidance for outdoor work in heat comes down to this:

• Move heavy work, like lifting, concrete pours and roof work, to the cooler part of the day.
• Put shade over rest areas and, where you can, over work areas.
• Give everyone free access to cool drinking water close to where they're working.
• Add more frequent rest breaks, somewhere cooler.
• Use mechanical aids to cut the physical load.
• Let people take PPE off while they rest, so their bodies can shed heat.
• Build new starters and people back from leave up gradually, so they can acclimatise.
• Find out who's more at risk, for example because of medication, a heart condition or pregnancy.

Brief the whole crew on the early signs of heat stress. Supervisors should check on people during breaks, not just at the end of the shift.

Water, sun and PPE on the day

Drink before you're thirsty

Thirst is a late sign. HSE says to drink cool water often and in small amounts, rather than tea, coffee or fizzy drinks. At a high work rate in the heat, that's about 250 ml every 15 minutes.

If your PPE stops you drinking while you work, drink about 500 ml an hour before you start, and the same during each rest break. You lose salt as well as water, so drinks with added salts help.

Cover up against the sun

HSE's advice for outdoor workers:

• Keep your top on.
• Wear a hat with a brim or a neck flap. On site, that means a brim or neck flap that fits your hard hat.
• Use sunscreen of at least SPF30 on any skin that's showing.
• Take your breaks in the shade.
• Check your skin, and see a doctor about any mole or spot that changes.

Don't strip off your PPE to cool down

The hazard that needs the PPE doesn't go away in a heatwave. Take it off when you're resting in a safe area, not while you're working. If PPE is making people overheat, that's a job for the supervisor to fix with breaks, timing or lighter kit.

Heat exhaustion or heatstroke: what to do

Heat exhaustion comes first. The NHS lists the signs as tiredness, dizziness, headache, feeling or being sick, heavy sweating, cramps and a high temperature.

If someone has them, follow the NHS's four steps:

1. Move them somewhere cool.
2. Take off unnecessary clothing, including PPE once they're in a safe area.
3. Give them plenty of water, or a sports drink.
4. Cool their skin with water and fan them.

They should feel better within 30 minutes.

Heatstroke is a medical emergency. Call 999 if they're still unwell after 30 minutes, or if they have hot skin that isn't sweating, a fast heartbeat or fast breathing, confusion, a seizure, or they pass out. Keep cooling them while you wait, with a wet sheet, a fan or cold water.

Construction site safety basics that don't change with the weather

More workers die in construction than in any other industry in Great Britain. HSE's provisional figures for 2025/26 show 25 construction workers were killed at work, out of 126 across all industries. Across all industries, falls from height caused the most deaths.

Heat doesn't replace those risks. It makes them worse, because tired, dehydrated people make mistakes. HSE notes that weather can affect how safely someone handles machinery. The basics every site runs on:

• A site induction. CDM 2015 says the principal contractor must make sure one is given.
• The right card. CSCS says all construction workers should hold the relevant CSCS card.
• Safe work at height, with edge protection, scaffolds and ladders checked before use.
• Vehicles kept apart from people, with a trained marshal directing reversing and deliveries.
• Emergency arrangements that everyone knows, including evacuation, tested at intervals.

Getting site-ready

If you're new to site, the Level 1 Award in Health and Safety in a Construction Environment covers these basics. It's the qualification you need to apply for a CSCS Green Card. You can take our Level 1 health and safety course on its own, or our CSCS Green Card package, which adds the test booking and card application. Our health and safety courses cover specific site risks. If vehicles are your job, read our guide to becoming a traffic marshal.

Frequently asked questions