Polygon Offset

hello, i am creating a 3d world with buildings which cast shadows onto the ground with the use of the stencill buffer.
But the shadows has something like black artifacts and this is ugly.
i used polygon offset to eliminate them but nothing hapens or i dont know how.
Can anyone help me…??

what do you mean for black artifacts? please share at least a screenshot, we are not gurus or clairvoyants :wink: