Did you know that one effect of a deeper new wall cavity is the additional footprint area required for roof and floor?

On a large building site this may affect the density or number of properties that could be built on the site, e.g. in the worst case, 4.00 m2 extra on the roof area for each property may mean that only 9 properties could be fitted in an area that may be able to accommodate 10 if the external walls were thinner.