A general rule of thumb is that the total cost of hiring a new employee is 1,5 her annual salary (interval between 70 % & 200 %).
To keep employees, the enterprise must also maintain a good reputation and good surroundings, which involve costs. Renovations permit to reduce those costs by increasing employee satisfaction towards the enterprise and the job.
Employee satisfaction increases when air quality increases and when the air temperature is more comfortable. With natural light, they see more clearly the task to accomplish and if windows allow them to have a nice view, they appreciate it
Results are obtained with standard energy efficiency measures. Examples include natural ventilation, skylights or additional windows, access to a view or to the outdoor environment.
You can find this information in a Quebec French adaptation of an American guide
or read the original: How to calculate and present deep retrofit value, a guide for owner-occupants, published by the Rocky Mountain Institute in the US.