A pretty amazing US federal government resource. It seems rigorously based, clearly explained, and covers design fundamentals and research. For example, the 'Productive' page has lots of clearly explained fundamentals I didn't know:

https://www.wbdg.org/do/productive

  In private sector offices, such costs are typically, in order of magnitude:

  * $200 per square foot per year for salaries
  * $20 per square foot per year for amortized bricks and mortar costs, and
  * $2.00 per square foot per year for energy.