The correct / appropriate temperature of your workplace depends on whether it is indoors or outdoors, and the normal operating temperature of that environment. E.g. if you are working as a snow shoveller, it shouldn’t be appropriate to expect a workplace of 20°C.
The law doesn’t actually state that there is a minimum temperature within a workplace. However, despite this, it is widely agreed that the temperature in workrooms should normally be at least 16°C or 13°C, if much of the work is physical.
The only inclusion of temperature within Health and Safety law is from The Workplace, Health, Safety and Welfare Regulations 1992, which states 'During working hours, temperatures in all workplaces inside buildings shall be reasonable'.
When working outdoors, the effects of the weather in this environment can have a very serious impact on an employee’s welfare. E.g. exposure to the sun can cause skin damage such as sunburn, blistering and skin ageing, which could lead to skin cancer.
For Hot environments and possibly sunburn, people can avoid unnecessary exposure by such means as:
Wearing long sleeve shirts or loose clothing with a close weave.
Wearing hats with a wide brim.
More frequent rest breaks.
Taking breaks in the shade when possible.
Scheduling work in cooler times of day.
If possible, provide shade where work tasks are being undertaken.
Sun protection is important. Sunburnt skin is damaged skin, and a suntan in not a sign of good health.
For cold environments, you can ensure that:
Personal Protective Equipment (PPE) is correctly issued appropriately.
Provisions of facilities for hot drinks are available.
Introduce more frequent rest breaks.
Educate workers about recognising the early symptoms of cold stress.
Ensuring that you keep warm and have the facilities to do so is vital to ensure that you have a safe workplace even when it is a freezing environment.