Site built and off frame modulars require a similar foundation, but site built plans usually have more piling and support girders. Most of our foundations can be completed in a week. The planning, engineered piling plan, and layout usually a little longer.
Most of our foundations are built with 8" X 8" treated wood pilings. Girders can be treated 2" X 12" lumber or engineered laminated beams (LVL's). All connector are hot dipped galvanized bolts,nails, and straps.
Site built homes on piling require about same amount of time to build. Modulars homes can be set on an elavated foundation and completed in about 4 to 6 weeks. One of the major cost differences for a raised home is the decks and steps. They are higher and usually larger.