The renovation planning process is filled with uncertainties and subjective decisions. These make the decisions upon what and when to renovate a complex and ambiguous problem. Selection of renovation measures related to building envelope are often far from optimal as decisions are usually made based on visual inspections. These are manned and thus prone to subjective assessment and the knowhow of individual inspectors. Furthermore, objective criteria which could indicate non-structural failures are often missing. The objective based planning process allowing the estimation of the current damage status of the building envelope by only using non-destructive measurements is still in its infancy. The first step requires establishing reliable and objective based data collection. These could be efficiently collected by Unmanned Aerial Vehicles (UAV) with subsequent image recognition algorithms allowing the identification of imperfections and store the position and extent of such deviations into the building’s digital assessment database. Such tools do not exist. The aim of this study is to investigate the current objectivization possibilities in the domain of building inspections. The first part provides a literature review describing how an autonomous UAV survey of a building envelope may be planned and what computer vision techniques may be used for automatic damage recognition and classification. Subsequently, an objective detection model based on the YOLO-tiny (You Only Look Once) computer vision framework is employed in a case study investigating a building envelope of historical Tjolöholm castle in Sweden. This study contributes to developing a methodology for an objective based visual inspection process.

In past decades, several performance indicators have been developed allowing to objectively assess current status or predict failures of material, components and other factors like moisture safety. However, each performance indicator requires its unique sets of data, which are often difficult to obtain. It is therefore of interest whether a combination of several indicators is applicable in older buildings which often lack readily available documentation. The aim of this study is to identify data gaps preventing the use of indicators and to ascertain whether missing data can be filled by combining visual inspections and non-destructive testing. The first part of the paper summarizes known building envelope related indicators and arrange them into three groups: general, hygrothermal and service life performance indicators. The second part is a case study where the applicability of selected performance indicators is tested against an in-house database consisting information about 610 buildings in Gothenburg. It was found that the use of performance indicators is limited as the gaps in the available data are present for all types of performance indicators. The material composition of buildings envelope was identified as the most substantial gap. This limited the use of hygrothermal performance indicators in 58.5% of the buildings.