Pressure treated plate is now fastened to the foundation with bolts or straps installed previously in the top coarse of block. The "P.T."plate is guaranteed not to rot, a common problem before pressure treated plates became code.
The joist size is dependent on the "span". (length of joist)
The joists are attached to the house with a "ledger" beam which is bolted to the frame on the foundation of the existing residence, if the project is an addition.