We are in the early planning stages of adding a screen porch to a home we're moving to in the Boston area. The plan is for a 12'x15' room with a shed roof, with the long dimension running along half the back wall of the two-story house. The roof ledger would tie into the existing wall studs just below the 2nd floor windows.
I have a few questions. The first relates to foundation options. The finished floor of the first floor is only about a foot above grade. A sliding door on the rear wall of the house steps down 6" to a concrete step that's 4'6" square and 6" above a poured concrete patio that extends about 18' back from the house essentially on grade (everything back there is pretty flat). My first thought was to pour a slab with an integral footer underneath the side that will support the roof posts. The slab would provide both foundation and floor for the porch. However, I've been advised to keep the floor of the porch close to the same level as the finished floor of the house, which would mean at least a 12" thickness (and I assume more, since the slab would need to extend below grade?). Seems like a lot of concrete, and $$!
The other option would be framing a wooden foundation on concrete footers. However, I'm reading that the concrete should extend 6" above grade, which doesn't seem to leave much space for posts/beam/joists. Also, I'd be concerned about insects/rot if the framing is so close to grade.
Second question- I'd like to enclose the porch using screen door panels with the option to switch glazed/screen inserts. Does that classify the room as a "sunroom" instead of a porch? If so, it seems like energy code requires u-value of 0.50 or less, which seems unrealistic for the door panels (though I don't have any specs).