Generally, the temperature in workrooms should be at least 16 degrees Celsius. If the work involves physical activity the temperature should be at least 13 degrees. However, this is only a guide and there may be local laws or best practice about temperature depending on where you are in the world.
As a duty holder, encourage your team members to discuss any concerns about the temperature in their work environment with you. Take temperature into account when allocating work and when carrying out risk assessments.