Short answer: If you edit your Gross Floor Area (GFA) to move space from one Property Use to another (ex: from a vacant property use to an occupied property use), or if you create a new Property Use, then you are probably seeing the time-weighted GFA, which can be different than what you entered. This is because the system has not had 12 full months to incorporate the new GFA value.
Longer answer ("in the weeds"): Say you have a 100,000 sq ft building that is 70% Office, and 30% Hotel. On Jan 1, 2017 an Office tenant vacates 10,000 sq ft and the hotel takes that 10,000 sq ft for an expansion of the hotel.
First, you update your Office Property Use to decrease the GFA from 70,000 to 60,000 as of Jan 1, 2017:
Second, you update your Hotel Property Use to increase the GFA to 40,000 sq ft as of Jan 1, 2017:
If you make this update on January 1, you won't see any change to your GFA.
But, on Feb 1, 2017, this is what you will see in Portfolio Manager:
These numbers are time-weighted to the most recent 12-month period. Here's how the GFAs are being calculated:
- On Jan 1, 2017, the most recent 12-month period is Jan 1, 2016 - Dec 31, 2016, so the change isn't in effect yet.
- On Feb 1, 2017, the most recent 12-month period is Feb 1, 2016 - Jan 31, 2017
- The Office's GFA is counting 1 month where the Office is 70,000 sq ft , and 11 months where the Office is 60,000 sq ft
- The Hotel's GFA is counting 11 months at 30,000 sq ft, and 1 month at 40,000 sq ft
- As each month passes the Hotel's GFA will grow by ~847* sq ft, and the Office's GFA will shrink by ~847 sq ft, until Jan 31, 2018, when your time-weighted Office will be 60,000 sq ft, and your time-weighted Hotel will be 40,000 sq ft.
- Think of this as sort of a "Current GFA" date, similar to your "Current Energy" date, or "Current Water" date, but this date is not based on your bills
If the changes described above are not made in an internally consistent manner (for example, if the “Current As Of” dates for the changes do not match between the two property uses, or if you decreased the Office GFA by 10,000 sq. ft., but only increased the Hotel GFA by 5,000 sq. ft.), you may end up with an inconsistent GFA for your property.
*You might be thinking: "Where did you get 847 - it is not 1/12 of 1000?" Correct, the tool is taking the 31 days of January divided by 366 days of this 12-month period which was a leap year. This allows you to change Use Details mid-month.