Historic buildings deal with climatic conditions differently to modern structures and ill-considered alterations to improve energy efficiency can cause irreparable damage to the architectural heritage. In transposing the EU Energy Performance of Buildings Directive into Irish law, protected structures were exempted from the new requirements. Nonetheless, many owners understandably wish to reduce energy consumption and increase comfort levels in their historic buildings. This paper looks at the steps taken in Ireland to provide guidance on best practice. The Department of the Environment, Heritage and Local Government, which legislates for heritage protection and building standards, recently published ‘Energy Efficiency in Traditional Buildings’ to provide practical advice on appropriate upgrading measures. The guidelines support conservation practitioners and decision-makers in meeting standards for retro-fitting while protecting the heritage.