Renovation projects play a critical role in upgrading the existing infrastructure and preserving the historical landmarks. Major challenges in the current renovation projects include lack of up-to-date facility geometric information and seamless integration of the proposed renovation with the existing parts of facilities, and the unforgiving requirement/ imperative to integrate technology upgrades without disturbing the historical fabric of the landmark. Availability of updated geometric information is important since it reflects the as-is geometric and spatial information. Building information modelling (BIM) and laser scanning have been used to overcome these challenges within the current practice. However, further process improvements, a working understanding of historical construction methodologies and a hands on investigation are required in these two technologies to establish repeatable processes as best practices for future projects. Challenges in using these technologies in the current practice have been analyzed in an iconic landmark renovation project. The case study was done on one of the largest gothic style cathedrals in North America which is currently undergoing a mechanical system renovation. The research team was involved in the mapping of the existing facilities, aligning the proposed systems with the existing systems and overcoming the spatial conflicts while implementing the proposed renovation. This paper highlights the challenges faced by the construction team as they worked on the ongoing renovation and the lessons learned from modelling and laser scanning of a legacy facility.