How to Stay Cool on Site During a UK Heatwave

Meta title: How to Stay Cool on Site During a UK Heatwave | Site Safety Guide

Image alt text: Trade worker on site in summer heat wearing breathable workwear Image credit: ITS Hub (reference only -- verify reuse rights before publication)

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UK summers are not what they used to be. The Met Office has recorded the ten hottest years on record in Britain since 1990, and forecasters are increasingly issuing heat-health alerts that stretch across entire working weeks rather than just a day or two. For trades working outdoors -- roofers, groundworkers, bricklayers, landscapers -- or those in unventilated spaces like loft conversions, plant rooms, and south-facing extensions, the rising baseline temperature is not just uncomfortable. It is a genuine health hazard.

This guide covers what you can actually do about it: from scheduling your day around the sun, to what breathable workwear really means in practice, to what happens inside your power tool batteries when they get too hot.

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What the HSE says about working in the heat

There is a common misconception that UK law sets a maximum legal working temperature. It does not. The Health and Safety Executive does not specify a figure at which work must stop. What the law does require, under the Health and Safety at Work Act 1974 and the Management of Health and Safety at Work Regulations 1999, is that employers carry out a risk assessment for thermal comfort and take reasonable steps to manage it.

In practice, this means employers have a duty to consider temperature as a workplace hazard just as they would a trip hazard or a dangerous substance. The HSE's own guidance recommends a minimum of 16 degrees C for sedentary work and 13 degrees C for physical work -- but no upper limit is stated. Instead, the guidance talks about "reasonable" temperatures and lists factors including air temperature, radiant heat, humidity, air movement, and metabolic heat generated by physical activity.

The practical implication for trades: you do not need to wait for a formal instruction to stop work if conditions are dangerous. If you are sweating through your clothing within minutes of starting, feel dizzy or nauseous, or notice that a colleague's behaviour has changed (confusion and irritability are early signs of heat exhaustion), those are grounds to take a break and cool down. No job is worth a medical emergency.

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The difference between heat exhaustion and heat stroke

Understanding where the line is matters on site, because the response is different.

Heat exhaustion develops when the body loses too much fluid and salt through sweating. Symptoms include heavy sweating, cool and pale skin, a fast but weak pulse, nausea, muscle cramps, tiredness, weakness, and a headache. A person with heat exhaustion is still conscious and sweating. The response is to move them to a cool place, have them lie down, loosen their clothing, apply cool damp cloths, and give them sips of water if they can drink. They should start to feel better within 30 minutes. If they do not, call 999.

Heat stroke is a medical emergency. It happens when the body temperature rises so high that the cooling system fails. Unlike heat exhaustion, the person may stop sweating entirely, have hot and red skin, a rapid and strong pulse, and may become confused, lose consciousness, or have a seizure. If someone on your site shows these signs, call 999 immediately and move them somewhere cool while you wait.

The gap between the two can be narrow on a hot, humid day with physical work involved. Catching heat exhaustion early is far easier than managing heat stroke on a busy site.

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Scheduling: the single most effective change you can make

The sun reaches its highest point and radiates the most heat between roughly 11am and 3pm in the UK summer. Shifting your start time to 6am or 7am and front-loading the physically demanding work -- the heavy lifting, the outdoor excavation, the roof work -- before midday is not just a comfort measure. It is the most effective single intervention you can make.

This is common practice in countries that routinely experience high temperatures, and it works for the same reason in the UK: you do the hard work in cooler air, take an extended break through the hottest part of the day, and come back for lighter tasks or indoor work in the afternoon.

Where scheduling is not fully in your control, talk to whoever is managing the site. A brief adjustment to the run-order can mean the difference between a productive day and a half-day off for heat illness.

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Hydration: the numbers that actually matter

The standard advice to "drink plenty of water" is correct but not specific enough to be genuinely useful on site. Here is the practical version:

In moderate heat with moderate physical work, the average person loses between 0.5 and 1 litre of sweat per hour. In hot conditions with heavy physical work, that can rise to 2 litres per hour or more. By the time you feel thirsty, you are already mildly dehydrated -- and mild dehydration reduces physical and cognitive performance measurably.

A working target for trades in hot conditions is approximately 250ml (roughly a cup) of water every 15 to 20 minutes during active work. That works out to around a litre per hour. Plain water is fine for most people over a normal working day. If you are sweating heavily for more than an hour or two, adding an electrolyte drink or salty food helps replace the sodium lost in sweat, which plain water alone does not do.

Caffeinated drinks are mild diuretics but do not cause significant fluid loss at the amounts most people drink. They are not the primary problem on a hot site. Alcohol, on the other hand, actively promotes dehydration -- a lager at lunch before an afternoon in the sun is a genuine risk factor.

Keep water in the shade. Water that has been sitting in a hot van or direct sun becomes unappetising quickly, and you stop drinking it.

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Workwear in the heat: what to actually look for

There is a real difference between a cheap cotton t-shirt, a standard work polo, and a garment designed specifically for heat management. The key properties to look for:

Fabric weight and weave. Lighter fabrics breathe better. A 150gsm polyester/cotton blend will move air better than a 280gsm cotton fleece in summer, obviously -- but within the same fabric weight, the weave matters. Open-weave fabrics or fabrics with moisture channels built into the construction move sweat away from the skin faster than plain-weave alternatives.

UPF rating. Ultraviolet Protection Factor works similarly to SPF in sunscreen. A UPF 50 garment blocks approximately 98% of UV radiation. For trades working outdoors for extended periods, a UPF-rated shirt covers the arms and upper body with zero ongoing effort -- you put it on and it works all day. This is meaningfully better than relying on sunscreen alone for areas that clothing covers.

Moisture wicking. A fabric labelled as moisture-wicking moves sweat from the skin to the outer surface of the fabric where it can evaporate. The evaporation itself has a cooling effect. Not all workwear marketed as breathable actually wicks effectively -- look for technical performance claims backed by a fabric specification, not just marketing language.

Colour. Pale and white fabrics reflect radiant heat more effectively than dark colours. This matters most for outdoor roofers or groundworkers where direct sun exposure is constant. Dark navy work trousers absorb significantly more solar radiation than khaki or stone-coloured equivalents.

Brands including Carhartt have released summer-specific workwear lines designed around these principles, and Makita has recently launched a dedicated UK workwear range with similar functionality in mind. The principle is the same across the category: construction-grade durability does not have to mean a thick, heavy, heat-trapping garment.

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What heat does to your cordless tools and batteries

Lithium-ion batteries -- the standard power source for virtually all modern cordless power tools -- have an optimal operating temperature range of roughly 15 to 25 degrees C. Performance starts to drop as temperatures rise above that range, and most battery management systems will reduce output or shut the tool down entirely above around 45 to 50 degrees C as a protection measure.

In practical terms, this means a battery left on the dashboard of a van or on a dark roof surface in direct sun can exceed the safe operating temperature before you pick it up. The dashboard of a parked car in direct sun can reach 70 degrees C or more on a hot UK day -- well above the point where battery chemistry starts to degrade.

The correct habit is to store batteries out of direct sun during the working day -- in a shaded tool bag, under a work vehicle, or in any spot that does not receive direct solar radiation. If a battery feels hot to the touch before you use it, set it aside to cool for 10 to 15 minutes rather than fitting it into the tool and running it hard.

Charging hot batteries is also a bad idea. Most modern chargers will refuse to charge a battery above a certain temperature and display a warning indicator, but the safe practice is to let batteries cool to ambient temperature before putting them on charge. This is relevant on hot days when the charger itself may be inside a hot site cabin or van.

The same logic applies to the tools. Angle grinders, circular saws, and combi drills generate their own heat during use. On a hot day, running a tool continuously at high load generates more heat than the motor management system can easily dissipate. Short rest intervals -- 30 seconds between cuts on a hot day versus continuous cutting on a cool one -- genuinely extend the working life of the tool and reduce the risk of thermal protection triggering at an inconvenient moment.

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Sunscreen as PPE: treat it the same way you treat gloves

The shift happening across the UK trade industry right now is that sunscreen is being moved out of the "optional personal item" category and into the "site PPE" category. Marley's 2026 Safe in the Sun campaign is one visible expression of this, but it reflects a broader trend: the Health and Safety Executive has published guidance acknowledging that outdoor workers receive far higher annual UV doses than office workers, and that skin cancer risk is occupational for people working full days outside over a 20 or 30 year career.

SPF 50 sunscreen on exposed skin, reapplied every two hours or after sweating heavily, gives meaningful protection. The practical barrier has historically been that stopping work to apply sunscreen feels awkward or unnecessary. The framing that helps is to treat it the same way you treat putting on safety glasses before cutting -- a 30-second task that prevents a potentially serious outcome.

Broad spectrum SPF 30 is the minimum effective standard for outdoor workers. SPF 50 is better. Water-resistant formulations hold up better through a sweaty working day.

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A practical heatwave checklist for site managers and sole traders alike

Before work:

• Check the Met Office forecast and heat-health alert status for the day.
• Adjust the start time to get heavy work done before 11am if temperatures above 27 degrees C are forecast.
• Brief the team on signs of heat exhaustion and the response procedure.
• Ensure cold water is available on site -- at least 1 litre per person per hour in hot conditions.

During work:

• Enforce regular water breaks every 20 minutes for outdoor workers.
• Ensure shade is available for rest breaks -- a tarpaulin or a van with open doors counts.
• Watch for early signs: slowing pace, confusion, unusual quietness, complaints of headache or nausea.
• Store batteries and tools out of direct sun.
• Rotate outdoor workers to shaded or indoor tasks during the hottest part of the day.

End of day:

• Do not leave batteries charging in a hot environment overnight.
• Ensure all workers are hydrated and feeling well before they drive home. Fatigue from heat illness is a genuine road safety issue.

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