The building code does not have any guidelines mentioning attachment an addition to the main house.  Home addition earthquake damage occurs when the connection between the old floor and the floor of the new addition come apart.  The individual contractor chooses how this connection is made. In most cases a contractor will put in enough nails to make sure the  addition does not fall down from gravity and at the same time give earthquake resistance zero consideration.   For this reason the building inspectors pass anything that looks reasonably effective in keeping the addition from falling down. On this web page you will learn how important it is to connect the addition to the main house.

Which Hardware Is Used To Prevent Home Addition Earthquake Damage?

Additions attach to the main house in a couple of ways.   For this reason a few types of hardware are used to attach an addition to the main house.  All of this hardware can be found in the Simpson StrongTie Catalog. 

The most common one is the Simpson SDS Heavy Duty Connectors.  This hardware screws two joists together when the contractor set the addition floor joist next to the original floor joist.  Look for bolts, screws, or nails when evaluating the contractor’s work.  If the connection looks weak, strengthen it with these SDS Heavy Duty Connectors.     To make sure the connection is as strong as possible make sure the screws go all the way though both floor joists if you screw them together.

Earthquake pushing home addition away from main house

                                        EARTHQUAKE PUSHING HOME ADDITION AWAY FROM MAIN HOUSE

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