My porch was put on later in the homes life and poured on a block foundation. The house has a stone foundation so they are completely seperate. I also get about 1" of water standing against the house. At first it leaked down the stone foundation and into the cellar. I caulked against the aluminum siding with "Big Stretch" caulking which will expand and contract with the porch. This eliminated the water leaking down the back, and most of the water will run off the side of the porch. However, water sitting against aluminum siding isn't that big of a deal, but it can't be good on cedar. I'm planning to tear mine out one of these days, and I'd recommend the same to you. You might try some flashing of some sort caulked in to keep the water from standing right on the cedar in the mean time.