Affordable housing contributions on sites of 10 dwellings or less - Public forum - Planning Advisory Service (PAS)

We have a commuted sums protocol for financial contributions towards affordable housing where the number of units on a site exceeds the 1000 sqm gross internal floorspace threshold identified in the Ministeral Statement of November 2014 and more recently through the NPPG.

I was wondering whether anyone else applies something similar and whether or not the floorspace of buildings to be demolished on site should be deducted from the gross internal floorspace figure. The building I have in mind is not in C3 use.