Ireland's Climate Action Plan (2019) set ambitious targets for existing dwelling retrofits, including retrofitting 500,000 existing dwellings to a B2-Building Energy Rating (BER) or better by 2030, at an average rate of 50,000 dwellings per annum. Various policies have been established for the achievement of these targets, including establishing One-Stop-Shop (OSS) retrofit delivery models, which aim to remove retrofit barriers by offering full-service retrofitting for homeowners. The success of policies established for the achievement of Ireland's retrofit targets depends on many householders deciding to retrofit, and the alleviation of persistent demand and supply-side barriers. This research evaluated existing OSS services and other retrofit services in Ireland, from the perspectives of householders who have completed or partially completed their retrofit journey using these services, and retrofit industry stakeholders involved in, or with expert insights into, Ireland's retrofit industry. The research evaluated the householder retrofit journey in detail, including the drivers which motivated householders to progress through each stage of their retrofit journey, the barriers that prevented them from doing so, and householders' experiences of engaging with OSS and other retrofit services in Ireland. In addition, the research examined the key challenges facing the supply side in enabling widescale retrofit uptake in Ireland. To do so, in-depth interviews were conducted with 17 householders, as well as semi-structured interviews with 25 industry stakeholders. The performance of implemented retrofits, including the multiple benefits received through the works, was also examined through a pre- and post-retrofit dwelling monitoring study of five case study dwellings in the west of Ireland. The research confirmed the importance of understanding the complexity of the retrofit journey, and establishing policies which address barriers at particular retrofit journey stages to increase their effectiveness. Various areas of improvement for both OSS and other retrofit services in Ireland were revealed, including changes to the policy landscape. The research also revealed that householders receive multiple economic, social and environmental benefits through retrofitting, but place most value on the social benefits, and highlighted the unintended consequences that can occur due to poor quality works and householders' practices within the home. Industry challenges, particularly relating to upscaling and upskilling the industry, were highlighted as critical challenges to address. Potential ways to address these challenges were highlighted. This research, therefore, presents in-depth insights that can contribute to the design of retrofit policy, and serve to inform how OSS and other retrofit services in Ireland can be improved to drive extensive retrofitting in Ireland. Recommendations for policy, industry and further research are presented.