Older homes were much smaller than they are now.  It is not uncommon for an older home (such as the 1955 house I live in) to be 900- 1200 square feet.  Over time demand for larger homes increased considerably and this was often achieved by building additions on the back of the house.

The building code does not tell a contractor how to connect an addition to the main house and if they are not properly connected, the addition can tear away with catastrophic consequences.   At that point the addition can lose vertical support and fall to the ground

In most cases a contractor will put in enough nails to make sure the  addition does not fall down after he jumps on it a few times and no consideration is given to future earthquake damage.  We have seen this many times.

Earthquake pushing home addition away from main house

                                                                             EARTHQUAKE SEPARATING AN ADDITION AWAY FROM MAIN HOUSE

Floor to Floor Connectors

Floor to floor connectors are special hardware made to keep an addition attached to the main floor.  Lag screws, machine screws, and nails are the most common types of connectors.  Assuming the two floors are butted up to each other Simpson SDS Heavy Duty Connectors  usually do the trick.  Be sure the screws go all the way though both floor joists if you screw them together.  They come in  1 1/2″ to 8″ lengths. Sometimes  custom made floor to floor  connectors must be designed on site. As far as the quantities go, the engineering principles discussed on this webpage will help you figure that out.  This connection is critical, make sure your contractor understands why it is so important.

 

                                                                                                                     SIMPSON HEAVY DUTY CONNECTOR

Floor to Floor Connectors

Floor to Floor Connectors attach the two floor together and make sure these two floors do not separate.  Hardware manufactures make them out of  bolts, large screws, and special hardware known as hold downs.  Alternatively, sometimes  custom made floor to floor  connectors must be designed on site as circumstances require.

Hardware used to prevent earthquakes from pushing addition off of main house

HARDWARE TO PREVENT EARTHQUAKES FROM PUSHING ADDITION AWAY FROM MAIN HOUSE