BASE HEADER

This is an emergency. Zero carbon cannot be achieved using low carbon sources. Low is not zero - and how low do you mean? This looks like a get-out option which should be removed.
Carbon offsetting is also problematic and too easily used as a get-out. "Burn now - offset later" should not be an option. Any offsetting for the building construction must be within the time frame of the building construction. Any offsetting required from the use of the building must be equivalent and run at the same time as the carbon usage.
The wording suggests WDC is not seriously committed to this. "Should", "expected" and "considered" do not mean the same as "must", "required" and "delivered". There should be no wiggle room and the policy should be explcit in defining what is required.