Nowadays, the Web represents the main way of providing computing services to a huge variety of users with different characteristics. Thus, accessibility and usability features become even more critical to a Web application's success. Researchers have been worried in providing mechanisms to serve as guidelines that Web systems should provide, in terms of usability and accessibility requirements. However, there not exists an instrument to provide a measure to help the specialists to verify how much these requirements are presented in a Web system. In this paper, we describe HEUA, a proposed questionnaire to assess the usability and accessibility of existing (or legacy) Web systems, to support measuring how much effort a Web system needs to be improved.