However, after deducting for the garage and the setback from the boundary, only 10 m width remains for the house,
Does "garage
and setback from the boundary" mean that the garage(s) are wider than the building line width? – how much width are we talking about
before these deductions? I suspect you are caught in an image of a certain building configuration, which, however, is not as given as it seems. Often a bold swing of the sword through the damn connecting door between the house and the garage suffices, and suddenly a much nicer house fits on the plot. With a bowling alley floor plan, you do yourself no favors.