1.1 Research framework
In the last decade, the topic of energy efficiency of the existing building is at the centre of the most recent Community and international recommendations: United Nations [1] and European Union have promoted many Directives - as EPBD Recast 2010/31/EC [2] and the Italian transposition in L.63/2013 [3] and DM 26th June 2015 [4]- with increasingly stringent performance requirements to stimulate deep renovations of existing buildings. Deep renovation means application of energy efficiency measures able to transform existing buildings into Net- Zero-Energy Buildings (nZEB) not only with standard technologies, such as insulating materials, insulated windows, advanced heating and cooling systems and modern lighting, but also using innovative technologies based on renewable energy sources [5].
Historic buildings represent more than 22.3% of European constructions dating before 1946 (in Italy the percentage is slightly higher - 30%) [6]. As basic assumption of this study, heritage buildings are a unique and unrepeatable cultural value testimony, expression of ancient constructive and material knowledge, to be preserved over time for our society (Code of Cultural Heritage 42/2004, article 3.1) [7]. Dealing with built heritage may lead to a paradox as the interventions aimed at achieving excellent performance values and cost savings could jeopardize the uniqueness of the existing construction. According to that, while regulations targets handle existing buildings, a ‘exemptions regime’ is provided for built heritage and the competent Authorities could decide in which cases law does not be applied if they “would unacceptably alter heritage building character or appearance” [2]. However, simultaneously, Governments are boosting buildings renovation through direct grants and tax incentives given as recognition of energy savings investments [9], also available for historic buildings owners, although they have to facing with the competent Authorities’ opinion.
At the same time, the 2012/27/EC Directive [10], transposed in Italy by DL 412/2014 [11], asks to the public Administrations to improve at least the 3% of the public dwellings each year to reach nZEB values; as proof of this trend, last Italian Ministry of Cultural Heritage campaigns with ENEA, “Heritage in energy rating class A" (tran. "Patrimonio in classe A”) (2017), fosters free energy check-up and encourages improvement actions on public heritage buildings [12].
The assessment of energy performance in a building provides the essential baseline for identifying the need for improvement measures [13]. It is evident that by conveying a message relating exclusively to the achievement of the best energy performance, the fundamental aspect related to protection is neglected, causing unsuitable interventions [14]. Even though heritage buildings should not to comply with minimum energy performance requirements as other existing buildings, retrofit strategies could be done to ‘improve’ the building performance as much as possible, without expecting to reach the top rating ‘adjusting’ the building components [8]. For what concerns historic buildings it is not possible to identify intervention strategies unique for each kind of building: there are objective difficulties to verifying performances due not only to their construction singularity, but also because their conservation state (thermal bridges, degradations, modifications of the ancient microclimatic system, etc.) [15]. Furthermore, buildings are dynamic systems that depend on the variability of external parameters, aspects such as ventilation, occupants rate, surface radiant temperatures and operating temperature should be considered in an energy evaluation [13].
As remarked by the international and national Guidelines and researches on this subject, this delicate context requires a careful evaluation of the impact of actions on the building 'metabolism'. The balancing between usability and protection, needs a procedure, structured on multiple criteria and adhering both to the principles of conservation and the efficiency objectives [16]. However, the same above mentioned researches, underlined the lack of an instrument able to guide both those who aim to plan retrofit interventions and those who must verify their feasibility. Any iterative process needs to be able to balance, in an equitable manner, the three areas of energy efficiency, environmental, sustainability and protection [8, 14, 15]. To this purpose, new and adequate assessment methods and tools are required.
1.2 Research Aim and Methodology
Starting from this framework, the research objectives are the following:
- Evaluation and implementation of Guidelines for improving energy efficiency in historic buildings;
- Development of a multidisciplinary and holistic methodology to assess and plan interventions in historic buildings: it should be the structure of a interactive platform, able to encourage the exploration of different retrofit scenarios advantages and possible effects on the building, checking their congruence with preservation and improvement criteria;
- Expanding knowledge about Mediterranean architecture, focusing on the southern European area.
This report sets out to discuss and highlight criticalities of existing retrofit methods (Section 1), to point out the actual findings of the research on-going – guidelines and case studies analysis - (Section 2 and 3), while a draft of the proposed methodology structure is presented (Section 4). Finally, next steps of the research and some suggestions will be exposed.
2. Assessment guidelines and methods overview
The existing gap between legislative barriers, regulatory exemptions and protection needs made the methodology to energy assess and improve the built heritage an open question [17]. One of the greatest challenge in this field is to define a guidance procedure, that could help stakeholders in selecting retrofit measures evaluating their pros and cons. Retrofit options need to be carefully weighed, to balance heritage criteria, users’ needs and efficiency objectives and consider different variables, case-by-case [14, 8].
During last years, a wide literature and many researches concerning the historic buildings have been carried out, to provide valuable instruments dedicated to energy retrofit planning and assessment. A review of existing studies has been done, as shown in the Table 1.