This paper presents an approach to integrate usability evaluations into Model-Driven Web development processes. Our main motivation is to define a generic usability evaluation process which can be instantiated into any concrete Web development process that follows a Model-Driven Development (MDD) approach. A preliminary version of a Web Usability Model was defined in order to support this usability evaluation process at several stages. This Web Usability Model decomposes the usability sub-characteristics (from the Software Quality Model proposed in the ISO/IEC 25000 SQuaRE standard) into other sub-characteristics and measurable attributes. Web metrics are intended to be associated to measurable attributes in order to quantify them. Our approach is intended to perform usability evaluations at several stages of a Web Development process. In this paper, we show how usability evaluations at final user interface (UI) can provide feedback about changes in order to improve usability issues at intermediate artifacts (Platform-Independent Models and Platform-Specific Models) or at transformations rules among these intermediate artifacts.