The wall-frame is built with 2 x 6 girts rather than 2 x 4 girts which is a “standard wall-frame”. The sandwich wall allows space for insulation to be packed into the walls before the wall liner is applied. Once insulation and liner are installed on the interior walls and ceiling, insulated doors and thermal-glazed windows complete the insulation process and the workshop becomes a useful winter facility for repairing machinery. Because it is so economical to do so, many barns are built with a sandwich wall-frame workshop on one end of a larger implement storage structure at the time of construction.
Even if the intent is to have a building (or a portion of a building) insulated at a later date, it is wise to have the structure built with sandwich wall-frame when the building is erected. After the construction, it is much more difficult to get a good insulation job if the walls are built to standard wall-frame dimensions and cost is not that much greater for sandwich wall.