The roughening transition is studied by low-temperature analysis for the Widom model and axial-next-nearest-neighbor-Ising-model (ANNNI-model). Low temperature series expansions are given for the second moment of the interfacial width and surface density, which are two types of roughening order parameters. A sine-Gordon renormalization group description of the roughening transition and related critical behavior is discussed. Low temperature series expansions are also given for the surface tension between coexisting plus and minus ferromagnetic phases of both models. Confirmation of positive surface tension along the roughening line is made in both cases. This establishes internal consistency of our analysis.