It is possible to add onto a mobile home. However, the structure of the foundation does affect whether or not an addition can be made. It is best to add rooms only on homes with frost line footings.
Mobile homes that are on foot piers sometimes shift when cold weather causes the ground to rise or drop on one side of the home. Room additions on mobile homes are not part of the original structure and may buckle or break at the jointed spot between both during this shifting. Homes with frost line footings rest on blocks buried below the frost line in the ground. These foundations do not shift during cold weather, so there is less risk of buckling with new additions.