Double wide mobile homes are built in one story sections on steel chassis that have their own set of axles and wheels for mobility. The chassis is a sufficient foundation for the home and does not need to be placed on a full foundation , although many double wides are. Double wide mobile homes are built under the standards set by the US Department of Housing and Urban Development, or HUD. These homes are often set on concrete piers, and tie downs are used to anchor them securely to the ground.
Modular homes are constructed, but not completed in a factory. Then the pieces are hauled on flatbed trucks to the building site, where they are placed on a permanent foundation and completed on site by local builders. Modular homes must meet local state building regulations.
Taken from~ ehow differences between modular and double wides