Joist hangers can help you mount each rafter to the house.
How to tie into roof for a covered porch.
The edge of the roof of the house and the frame to the porch should be seamless now.
I said all of that to say this.
I am no framer.
Use screws to secure the rafter to the sill plate.
The blocking is held low to hide the roof wall intersection and to provide a 1 inch air space at the top for a ventilation channel.
When a shed roof ties into an existing roof the new roof could be a simple lean to that covers a deck or porch or it could be the shed roof of a substantial addition.
The roof deck is 1x6 attached to the top of the rafters with 1 4 inch space between boards.
Each 2x4 joist should extend across the frame by going from the house edge to the porch edge.
Measure the sightline clearance height from the roof to the house not the other way around.
Make sure the 2x4 joists are turned so the boards narrow edge faces the floor of the porch.
Using lag bolts and a screwdriver fasten the base of the posts to the ground.
The porch roof may match the pitch of your home or have a more shallow roof pitch.
Those 2x s create the bottom of your new valley and your jack rafters on the porch roof will extend from that up to your new ridge board.
On a two story house you can usually tie the ledger into a band joist also called a rim joist located between the floors as shown below.
Install the 2x4 joists with some screws and brackets to the house edge.
You could cut the new ridge board into the existing roof and tie it into the house rafters or trusses but i am not sure that is necessary.
You can either remove the eave or just keep it.
The positioning of your rafters will depend on the pitch of the porch roof.
Measure the size of the beam that you are going to use.
Position the rafters on top of the sill plate.
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