Barriers to the growth of granny flats include municipal statutes, zoning laws, building restrictions, neighbourhood covenants and other regulations.
New construction is, of course, usually more expensive as well. Connecting utilities can also be expensive. Some municipalities require that driveways and/or off-street parking be provided for the granny flat occupant, and that can add expense, or be completely unfeasible for certain properties.
The growth of the prefabricated or modular building industry has made it easier for some homeowners to add a granny flat, but this type of structure may be prohibited in some localities.