Prefab vs built on site

The companies that sell prefab ADUs are vey good at marketing their products but many fail to tell the whole story. Several companies outside of California build ADUs that do not meet California's building code. The total construction time can be shorter than with an ADU built on site, but just by a few weeks., prefab companies make it sound like they will be working at your property for a few days, which is not true. A prefab ADU still needs a foundation and needs to be connected to the utilities. These are usually done while a built on site ADU is being built, with a prefab these are done before and after the ADU is delivered increasing their construction time at your property. Also, there is a cost that a prefab ADU will have and a built on site will never have, a crane. A crane is needed to position the ADU on your lot, this can cost anywhere from $15,000 to $25,000. Also, it may be impossible to install a prefav ADU at your house due to power lines or trees getting in the way of the crane and cranes can't drive on narrow or curvy streets either. A built on site ADU may be around thge same cost of a prefab and offers way more options.

Prefab companies usually only talk about the cost of the ADU per-se when giving a quote, they don't mention the foundation or the costs to connect the ADU to utilities, the fees the utility companies may charge or the cost of the crane needed to position the ADU on your lot. At the  end of the day, the cost of the whole project with all items included will be very similar between both ways but a built on-site ADU will meet California's building code for sure, will have many more options on size, shape, finishes, etc. A custom built ADU will be truly yours