One of the biggest mistakes I see when looking at other builders homes is that when the front concrete porches are poured they are poured right up against the siding. Which tells me that they are using the siding as flashing. The purpose of the flashing is to protect the floor joists from getting wet so they don’t rot out over time.
The proper way to protect your floor joists around the front porch area is to use aluminum flashing because aluminum will not rust or rot away.
If the siding on the home is used as flashing as I mentioned earlier, yes it may work for a few years, but what do you do when the siding needs to replaced. For example, cedar siding will rot out over time if it is has concrete poured up against it. Once it rots, no more flashing. If vinyl siding has concrete poured up against it, what happens when it cracks from being kicked or a chair leg bumps it.
When installing the flashing make sure the bottom of the flashing is 3″ to 4″ inches below the top of the foundation. The top of the flashing needs to be at least 6″ above the top of the finished concrete porch. Cut around door openings and foundation walls. See picture as example.
We use aluminum flashing on all our porches and you should to.