Most mobile homes, particularly older ones, do not have the weight-bearing capacity to have a second story installed. The choices are to build a shell over the existing mobile home and tying the house's systems together, which is nearly as expensive as building a new home, or building a two story garage addition and attaching it to the existing mobile home. Zoning regulations are more likely to permit the attachment of the two story garage to the original mobile home. In addition, the overall cost per foot of usable floor space is less with the garage option.
Settle whether you want to build a self-supporting structure over the mobile home or a two story garage to attach it to the mobile home. Consult a contractor and get his recommendations. Contact your mortgage company, if any, and determine what requirements they have for expansion.
Acquire zoning approval for the expansion and post the approval. Purchase construction materials and determine the exact method of connection of the two structures. Frame whichever structure has been approved.
If you are building a platform over the original mobile home and the plans have been approved, tie in the electrical system of the trailer and the second story platform in the manner that the zoning commission approved. Do the same with the heating and venting systems.
If you are building a two story garage and attaching it to the original mobile home, it will connect to the house with a breezeway, a sun room or even a traditional room such as a family room. Frame this connecting room and attach it to the garage and the mobile home before adding siding or exterior walls. This addition will most likely use a separate electrical box and heating and cooling systems and will not be tied on to the original mobile home.
For both the construction options, complete the framing, wiring, plumbing, heating and air conditioning installation. Install the exterior walls and the drywall. Paint or wallpaper the interior.
Install siding or other exterior cover on the outside walls of the home and blend with the existing siding on the mobile home. Alternatively, replace the siding on the mobile home to match the new work. Complete any required final inspection by contractor or zoning.