To provide a method for producing a ground sill of a service entrance porch, which facilitates construction of the service entrance porch.

The method for producing the ground sill of the service entrance porch, is carried out by setting an almost U-shaped ground sill in front of an outdoor-side erect surface of a building foundation, and attaching a floor plate on the ground sill. According to the method, a form 12 structure is obtained by fitting internal frames 11 into an external frame 10. The rectangular external frame 10 is formed of side frames 8 and side plates 9 and set on a bottom plate 7. Each internal frame 11 is shaped like the inverted U in cross section, has a bent piece 18 at a lower edge of each of a pair of side surfaces 19, at least one air hole 21 in each of the other pair of side surfaces 20, and at least one projection 23 on an upper surface 22. Then, concrete 13 is placed into a space which is enclosed by the external frame 10 and each internal frame 11 of the form 12 and has a width almost equal to that of the bent piece.