attaching ridge beam to existing house
As Scuba noted, a ridge BEAM is a structural element specifically designed to carry roof weight (typically half the roof load). A ridge beam must be designed by a qualified professional, and because the supports are critical, part of the design of the ridge beam is a set of details of the connection between the ridge beam supports and the ridge beam itself. If you have a ridge beam, you must support it correctlly, meaning the roof load must be carried down through the framing to the foundation.
If you have a ridge board, as Scuba noted, you have a non-stgructural element, which is held up by the rafters. If you don't know which you have, I recommend you seek professional assistance in developing a framing plan.