Synthetic polymer based roofing elements of the shingle or tile type are provided whereby adjacent roofing elements have projecting tabs or nibs that are adapted to engage against side edges of adjacent shingles or tiles when laid up in courses on a roof, and wherein there are relatively flexible stress relief zones in the shingle or tile adjacent the tab or nib projections, adapted to be deformed within their elastic limit when the shingles or tiles are subjected to stresses due to thermal expansion and contraction, with the stress relief zones also being adapted to return to their original non-deformed condition when such thermal expansion and contraction forces are relieved.