## 3 Literature Review  
### Methodology  
This research followed a descriptive Literature Review (LR) through the steps shown in Figure 2. Once the scope was cleared, the following research question was formulated: _\"What experimental and mathematical methods are employed in the field of cultural heritage to study moisture induced stress and strain in wood objects and wood buildings?\"_. Then, the necessity of a LR was clarified. These three achieved goals, i.e., define the topic, define the necessity of a LR, and formulate the research question, are part of step 1, which is entitled **Literature review (LR) planning**. To address the LR objectives, a total of six steps were followed.  
**Literature review perform** (Step 2): To avoid bias in the results due to the author's experience, a clear methodology was defined. The material was obtained by searching keywords in three electronic databases: Scopus, Web of Science Core Collection, and Google Scholar. The selected keywords, with relative Boolean logic operators, were reported in step 3 in Figure 2. Their choice was driven by the attempt to obtain a thorough and complete overview, which started from a large number of papers not limited to the investigated field.  
**Primary study selection**: The primary studies are those skimmed through in step 4. Their selection comprised three sub-steps: (_i_) the primary and (_ii_) the secondary searches, as  
Figure 2: The six-step literature review methodology is followed to perform a descriptive literature review: step 1 is literature review planning, step 2 is literature review perform, step 3 is keywords search, step 4 is primary study selection, step 5 is data extraction, and step 6 is content analysis. Asterisk (*) in step 3 is used to finding words that start with the same letters, e.g., experiment* finds either experiments or experimental.  
well as (_iii_) the snowball tracking. The literature obtained after steps 2 and 3 was evaluated by reading the title, abstract, and conclusions (_i_). Then, a further step of evaluation was performed by reading the full text (_ii_). The number of selected studies was enhanced by using their bibliographies, i.e., snowball tracking [30]. The main inclusion criterion was relevance to the research question. At the end of that step, the set of final primary studies was obtained.  
**Data extraction:** The data relating to each primary study was extracted and synthesised. Collected data was organized in an Excel worksheet to provide some bibliometric information, including the title, authors, first author's country, author's keywords, and publication details (i.e., year of publication and type of publication). Finally, the content of the document has been carefully analysed and clustered by topic; thus, a skeleton structure of the paper was organized. The classification and processing of the data extracted allowed us to answer the research question and conduct qualitative and descriptive analyses.  
**Content analysis:** After the classification and summary of the research findings, in this step, they were reported in a critical and analytical way. Within the discussions and conclusions sections, we present results we discussed, highlighting advantages and drawbacks of experimental methods and mathematical modelling. As a final step of the content analysis, the paper analysed gaps and conceived possible future research directions.