I’m assuming this porch has steps. I’m also assuming that, once on the porch, one can enter the house via a door. In this case, how much higher is the main floor of the house from the top of the porch. To rephrase, do you step up to enter the house from thew porch? And if so, by how much (feet, inches, or whatever)?
In my project situation, the porch was actually a small (3’x 5’) landing with several steps, which I expanded using footings, and pressure-treated wood for the frame and decking. The finished product was about 8’x 12’, with a roof, and almost completely covered the existing landing, steps, and a portion of the walkway. I did not have to remove any part of the original porch, and unless you had say the house before the addition, you would not know what was underneath.
I’m in Pennsylvania, close to Philly. The climate is bad in winter, but not as bad as yours. Still, the porch has held up very well in the last 6 years.