LAUSR

Timber structures are an important part of the Architectural and Cultural Heritage. Therefore, any action concerning the conservation, repair, retrofit, and monitoring of the built heritage cannot prescind from understanding how timber structures behave from the material level to the whole structure. The selection of manuscripts included in this special issue aims at supplementing the existing knowledge on the topic. The articles cover a wide variety of aspects, from the material assessment and structural analysis to the design and evaluation of retrofit strategies. In order to promote the preservation of the cultural heritage by favoring minimal-impact restoration strategies, it is very important to know how the structures were originally supposed to behave. To this regard Tardini (2018) presents an interesting review on the evolution process undergone by design principles for timber elements, from heuristic rules and geometric proportions to scientific-based criteria. A particularly important role in this process to which contributed people of the caliber of Andrea Palladio, Galileo Galilei, and Claude-Louis Navier, just to name a few, was played by Pierre Bullet’s table as clearly evidenced in the article. A large portion of the timber-built heritage is composed of the roofs and diaphragms present in unreinforced masonry buildings that include an extremely wide range of typologies, differing from each other in many aspects such as the layout and arrangement of the components, the type of decking, framing system and carpentry joints. Faggiano et al. (2018) present an inventory of roof and floor structural typologies used in monumental heritage buildings by referring to the iconic case-study of the Royal Palace of Naples built in the 17 century. Ten hall rooms have been analyzed by the authors, focusing on six roof types and three floor types. Blaha et al. (2018) report a peculiar example of cultural contamination regarding timber roof structures in Czech Republic. The authors studied the unique case of a building in Prague where the original Gothic roof was replaced with an Italian Baroque roof (by architect Martino Allio in 1685). The comparison of the Gothic roof and the Italian Baroque roof to a typical Czech Baroque roof resulted in some very interesting findings. It appears evident that the possible scenarios when intervening on timber-built heritage are potentially countless. Therefore, in addition to being effective and reliable, assessment procedures and analysis models need to be characterized by simplicity and versatility. In the article by Bertolini Cestari and Marzi (2018), a multi-disciplinary analysis of the issues related to the conservation of heritage timber roof structures is presented. The authors’ considerations and remarks stem from the experience acquired during thirty years of working on research projects. Ten case-studies located in northern Italy (five of which are included on the UNESCO World Heritage List) are analyzed to support the authors’ point of view. Mosoarka and Keller (2018) present instead a new procedure for the assessment of historic timber roof structures. The methodology relies on a multi-disciplinary and transdisciplinary approach that, in addition to providing a cost-effective condition assessment, aims at regulating future interventions based on a priority list. Macchioni and Mannucci (2018) focused their attention on the “triangular truss” which is the most representative structural assemblage of historical roofs in Italy. The article, after a thorough description of the most common features of the Italian trusses, analyses in detail all the aspects of the assessment procedure, from the viewpoint of the wood technologist. The discussion is further developed by addressing some case studies. Sousa and Neves (2018) investigated the application of structural reliability concepts to existing timber structures. Traditional semiprobabilistic methods usually adopted for the design of new structures are compared with probabilistic methods. For a better understanding, the target reliability indexes, defined by the authors by balancing costs and hazards, are illustrated by using a case study. Reliable and effective assessment/intervention procedures can only stem from accurate knowledge of the mechanical behavior of the various components. To this extent, invaluable insight is certainly provided by experimental testing performed both onsite and in laboratory. Branco et al. (2018) performed onsite INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE 2018, VOL. 12, NO. 4, 505–506 https://doi.org/10.1080/15583058.2018.1453327