We are lucky in that the previous owners were the architects who
designed and built the house. There are a few obvious potential areas
for expansion that they recognized when they built the house. There are
a couple of areas of 'loft' space above the garage that could be
converted, so they built reinforced lintels into all the walls where
you might want doorways, there are proper flooring joists in the space
above the garage and the garage walls are double thickness.