**1. Introduction**

 In Europe, 40% of the total energy use and 36% of CO2 emissions originate from the building sector. The aim of the European Union (EU) is to reduce its greenhouse gas (GHG) emissions by 80% by 2050. This is reflected in all the EU Directive ([1–3], pp. 1–56). Thus, the building stock plays a major role in achieving the 20-20-20 strategic targets. However, unless other avenues are explored to reduce the environmental footprint attributed to the existing building stock, the EU target may not be met. Due to climate change protection, energy consumption is required to be checked through greater efforts and concentration on existing buildings. According to ([4], pp. 1–87) building professionals need to provide more energy-efficient

refurbishment of existing buildings to bring them to modern sustainability standard. However, the possibility lies in adapting and retrofitting existing buildings to the optimum energy efficiency standard ([5], pp. 1–62). The concept of sustainable development could be applied to sustainability of Heritage buildings as any interventions to extend its lifespan without compromising its future and context. In conservation literature, different interventions are found and the term is used as a collective noun which encompasses any works to change, modify, repair or maintain the historic environment in good condition as well as preserve its historical and cultural value or significance. This is discussed in ([6], para 6.11) as "Interventions and Judgement" and as the "action that has a physical or spatial impact on a historic building or its setting."

 Generally, the terms used to describe interventions create overlap with other definitions and are often used as synonyms. Prudon [7] defined retrofitting as the act or process of making possible a compatible use for a property through repair, alterations, and additions while preserving the features which convey its historical, cultural and architectural values. More often, retrofitting could involve modernization and change in use (i.e. adaptive reuse). It is considered by [8] as the best way of preserving buildings. Meanwhile, ([9], pp. 155–157; [10], pp. 143–156) referred to retrofitting as similar to the term refurbishment, which does not only extend the life of a building, but also define a new purpose for it according to the demands of modern life. Thus, in this paper, retrofitting is used interchangeably with adaptive reuse.

## **2. Adaptive reuse of built architectural, cultural heritage**

Several scholars ([11], pp. 287–94; [12], pp. 543–56; [13], pp. 529–42) have acknowledged the growing trend in the move to building re-use and adaptation in the built environment. They suggested that some form of adaptation might be able to reduce the impacts of climate change on the built environment. Other authors ([14], pp. 88–103; [15], pp. 43–66) have posited that adaptation is an effective strategy for improving the sustainability of existing buildings along with its potential of giving extension of life to a building. The authors argued that by reusing existing buildings, lower energy consumption can be achieved thus making a considerable contribution to sustainability. With the advantage and possibilities of extension of life for buildings, adaptive reuse could also play a significant role in meeting the growing demand for regeneration of the built environment ([16], pp. 554–70).

According to Langston et al. ([17], pp. 1709–18) adaptive reuse has become an essential strategy to improve the environmental, financial and social performance of buildings. The environmental concern in adaptive reuse of buildings has been acknowledged by other researchers [18–20] in historic preservation. Therefore, it is seen as vital to sustainable development ([21], pp. 1709–1718) and considered applicable to the present climate change adaptation agenda. It is acknowledged that reusing existing facilities are related to sustainable development and in order to promote sustainability within the built environment, many buildings of cultural and historical significance are being rehabilitated. However, little attention is given to improving their operational energy performance. Several factors have since been advanced to be driving the adaptive reuse of buildings such as its value as a practical approach for delivering buildings for new uses, cost-effectiveness and rising energy costs. Latham ([18], p. 8) noted that adaptive reuse is cheaper than new development as it is a way of banking the built environment. Further, he argues that "transforming uneconomic buildings using green materials have the potential to enhance efficiency, comfort and life span of the building". Meanwhile, van't Hof cited in

([15], 43–66) opined that economic considerations have been the major driver behind adaptive reuse although other motives might have also been considered.
