Environmental sustainability in buildings is an important part of preserving the environment and reducing climate change. The increasing amount of physical infrastructure systems in Malawi has not been accompanied by policy-makers clearly understanding perceptions and attitudinal behaviors of building designers to promote environmental sustainability. Some building designers in Malawi might not be practicing sustainability innovations adequately, requiring more research to understand their perceptions and behaviors. The purpose of this mixed methods sequential and explanatory study was to explore how building designers' behaviors relate to the implementation of sustainability innovations in Malawi. Ajzen's theory of planned behavior explaining how attitudinal behaviors relate to individual's actions, served as the conceptual framework. The central research question investigated perceptions and attitudinal behaviors building designers hold about sustainability, and how these behaviors connect with practicing sustainability innovations. Data collection used a Likert scale questionnaire to capture behavior items. A sample of 99 individuals working in building organizations completed the questionnaire. Multiple linear regression analysis showed attitude behavior influenced practicing sustainability more than the subjective and perceived control behaviors. Interviews with 24 participants supported the analytical finding. Government and policy-makers were the target audience. Knowledge about behaviors toward sustainability innovations enables government and policy-makers strategize and change stakeholders' mindset to increase sustainability practices thereby impacting societal change in the construction communities.