My wife and I have a 91 year old beach house in southern California. The kitchen was added on about 50 years ago and is supported by 4x6s on blocks. There were concrete step leading to the back yard from the kitchen. After all those years the infrequent rain had done it's damage causing the bottom of door frame and floor boards around the door to rot. Now due to the rot the floor is bowed and we cannot fully open the back door.

I'm planning on pouring a concrete foundation and so far I've replaced the rotted 4x6 but I havent replaced the door frame or floor boards yet because I do not know how to support the rear exterior wall of the house to do so.

I cannot support it by the roof rafters because they too have rotted and dont trust that they can support the weight at the ends.

Any advice is greatly appreciated!