The typical Maltese traditional deffun roofs, with similar counterparts in many Mediterranean countries, are made up of layers of porous materials (in Malta, limestone, and lime-based overlying layers, with the final layer being made up of lime and crushed pottery to prevent water ingress). These roofs always had a slight slope, allowing rainwater to quickly run off and collect in the cistern which every house had.
These types of roofs are considered to be “breathable” in virtue of their ability to absorb and release a little of the incident moisture, even from heavy dew on a hot summer’s night, resulting in a cooling evaporative effect on drying. These types of materials have been commonly used in hot climates for hundreds of years, but this passive and sustainable technique has lost its popularity. With the prospect of hotter summers facing us in the future, and the drive for sustainability and reduction in energy consumption, there has been a revival internationally of the study of the so-called “cool roofs”, of which the local ones can be considered as a very good example.
A two-year MCST-funded Project EO4HBCS (Earth Observation for Historic Building Conservation and Sustainability) studied for the first time the thermal properties of Malta’s traditional roofs and compared their behaviour to the hybrid (for example traditional but with an overlying membrane) and modern roofs that are now widespread all over Malta and Gozo. The overall aim was to gather and analyse baseline geospatial, radiometric and in situ data from specifically chosen representative roof types, to compare their behaviour and, depending on the results, to promote the maintenance and even reinstatement of such traditional roofs on historic and traditional buildings. The innovative results of this project, which was led by researchers from the University of Malta: Prof. JoAnn Cassar, Head of the Department of Conservation and Built Heritage, and Prof. Charles Galdies from the Institute of Earth Systems, have been published in a scientific journal and communicated at a conference held at the Fraunhofer Institute for Building Physics – Fraunhofer IBP.
The thermal behaviour of these roofs has been studied in this project by using a combination of orbiting satellite, drones (UAVs) and in-situ (external and internal) sensors, as well as by using weather data gathered in close proximity to the roofs. Here, the aim was to identify their seasonal temperature and moisture gradients using simultaneously these three sampling methods. . This project also aimed at the potential identification of different roof types remotely (by UAV and/or satellite), in order to map out and quantify this resource and thus enable policy on these roof types to be formulated.
This study used a multisensor fusion approach for rooftop material characterisation, particularly, by satellite and collocated and cotemporal drone remote sensing. Radiometric analysis showed that very high-resolution data derived from KOMPSAT 3A satellite does in fact allow for the specific identification of traditional roofs – as distinct from the others - using the blue and red wavebands. This technologic synergy augurs well for a future, wider application aimed at the geospatial detection of traditional roofs at a national scale. This will be a tool of great practical use to heritage professionals as well as urban planners and regulators.
More importantly perhaps, results showed that the behaviour of the traditional roof type is indeed exceptional and different from the other roof types, and gives the best compromise between potential dispersion and insulation assessment in thermal performance characterization. More research and data analysis is needed to better understand these processes, but these first studies are pointing indeed to the traditional deffun roof being the “cooler” type.
In the longer term, this information will be used to develop recommendations and guidelines to safeguard buildings still having these traditional roofs and to develop a way forward to apply this research methodology in the wider Mediterranean. All of this is closely linked to potentially regaining the sustainable use and reuse of historic buildings, including reducing energy consumption and ensuing CO2 emissions, and possibly also affecting in a positive way the Urban Heat Island effect. This could be achieved also by a modern “modification” of the traditional roof type for use on more modern buildings –this research is still at planning stage.
Project EO4HBCS has been financed by the Malta Council for Science & Technology through the Space Research Fund 2019, CONTRACT NUMBER: SRF-2019-2S1. Project data merging and analyses were carried out by SISTEMA GmbH – the great input of Dr Stefano Natali and Alexandra Bojor is gratefully acknowledged. The project leaders wish to thank for their contribution to the project Heritage Malta, the Restoration Directorate, Architect Edward Said, Fernando Mifsud (Villa Frere) and Fabio Scicluna (Research Support Officer II), as well as Pilots Jason Gauci and Kevin Theuma (Institute of Aerospace Technologies, University of Malta) for their tangible support to this project. The project would also not have been carried out to a successful end and without the great support of Research Officer Ing. Elizabeth Muscat Azzopardi.
Anyone interested to learn more about this project can contact Prof. JoAnn Cassar or Prof. Galdies. Further information can also be found in the open-access paper A New Approach to Studying Traditional Roof Behaviour in a Changing Climate—A Case Study from the Mediterranean Island of Malta, Heritage 2021, 4, 3543–3571. A further paper has been presented at, and will be published in the proceedings of the fourth International Conference on Energy Efficiency in Historic Buildings (EEHB 2022) organised by the Fraunhofer Institute for Building Physics IBP.