Adding a room (or extension) to a mobile home will often involve new foundations for what will essentially be a separate structure, however, "mobile" homes with more permanent foundations can be extended with a stick built addition. Consideration should be given to the height of the new addition, since this will have an impact on the ease with which it can be sealed to the main structure.
A higher or lower attachment, for instance, makes it easier to attach and seal roofing, although such attachments will also require steps or ramps.
To prepare the foundations, footings may be poured or built from cinder blocks or piles. The choice of foundation largely depends on the frost line depth in the area. The further north in the country that a mobile home is located, the higher and more robust the footings will need to be. In frost-free areas, footing pads are generally sufficient.
Once the foundations and footings are laid, the timber framing for the structure can be erected. The quality should at least match, if not surpass, that of the existing mobile home. Insulation is also worth investing in before installing the vinyl siding.
To attach the extension, boarding should first be affixed to the mobile home for new boarding to meet. The edges can then be sealed with weatherstripping.