The wood structure that comes in contact with the concrete is extremely susceptible to mold and decay and needs to be protected with flashing. A self-adhering flashing product that has substantial thickness (25 mils or heavier) is the product of choice for this application.
Below the door is a critical area of concern and quite tricky. If there’s access to the door rough opening, the ideal flashing method would be to install a stainless-steel sill pan with an exterior lip. This will help prevent moisture from creeping between the subfloor and door threshold (Above). If stainless steel is not an option, cover any areas where the aluminum or galvanized flashing touches the concrete. This will prevent the concrete from eroding any non-stainless metal over time.
The most crucial element to the concrete stoop is the slope of the upper tread or landing. Sloping the landing slightly dramatically decreases the amount of moisture that reaches the wall intersection (Below). A stainless-steel piece of flashing with a kick-out bend finishes the detail. A PVC trim board beneath the door threshold can finish out the detail for a pleasing aesthetic and will also provide support for the threshold.
Joshua D. Blake, PE
Check out this story for instructions on how to pour a stoop.