If you will thatch sun porch to house it must have a foundation under it just like your home or in time it will pull away from your home, besides you must follow city codes or you could be taking it down only to put a foundation under it, check your building codes each place is different.

Or you can use a floating foundation deck system.

www.deckplans.com

Am trying to build a sundeck. A portion of the base in a concrete patio and the other side is dirt. I have solid concrete blocks to use as the base support, but is it necessary to use them or should i just dig hole in dirt and pour concrete, plus bolt the uprights to the patio?