Buildings can be developed on a net lot, as in the previous case; i.e., without changing the initial lot, or changing its shape but without changing the overall area. But in some cases there is a need to include in the operation not just the lots land, but also that which will be needed for non private uses, according to the legal binding conditions in each case.
In Spain, for instance, if you are building on previously undeveloped land, you must create the streets and allow for the location of gardens and other public facilities that will be used by the new dwellers (in Spain it is usually compulsory to locate public gardens, even if all homes are individual and with their own private gardens). There is also a certain amount of on –street parking, which requires also a certain space. Each planning law and each plan set a different quota for each of these surfaces.
To produce a rapid back of the envelope calculation, you can consider that a floor area ratio of 1 requires a surface for public facilities and streets that is the same as that of private lots. So, if FAR is 1 overall, FAR on the net lots, which will be just 50% of the land, will be 2, as usually any building on public facilities is not taken into account (FAR is calculated for floor spaces that are lucrative for the developer). So, you will not understand the full meaning of FAR unless you know the scope on which it is calculated…. And it must be acknowledged (there form based codes are right) that the figure itself doest not allow to kwnow the resulting urban form: just reminding yesterday and today’s posts, 1 sq m/sq m as measured on net lots allows for individual housing on rows, but 1 sq m/sq m (or 1 sq ft/ sq ft, which is absolutely the same thing) on a larger area usually asks for a different urban morphology.