Architectural Form and State of Conservation: A Case Study from Damage Maps Using Drone

The Sustainable Development Center of the University of Brasilia is one of the modernist buildings that make up the Darcy Ribeiro campus. The architectural project contains several recommendations for the execution of the flat roof waterproofing system, as well as details for rainwater runoff and drainage, which reveals a certain concern with watertightness. The research seeks to identify the relationship between the pathological manifestations recognized on the roof and the semicircular shape of the building, assessing the state of conservation through the use of damage maps as an analysis tool. The article is based on a field survey using aerophotogrammetry with a drone, the application of vector drawing software for graphic representation and discussion of the possible causes, agents and mechanisms of degradation at work. The results show the importance of mechanical protection for the good performance of the waterproofing system, as well as the need for correct sizing of expansion joints in order to absorb and relieve the stresses caused by hygrothermal variations. The methodology incorporated proved to be effective and economical in diagnosing and monitoring pathological manifestations, making it possible to plan maintenance actions that extend the useful life and preserve the intrinsic characteristics of building systems.

Keywords:

Subject: Engineering - Architecture, Building and Construction

1. Introduction

The Sustainable Development Center of the University of Brasília – CDS/UnB, located on the Darcy Ribeiro campus in Brasília and designed by Cláudio Queiroz in 1998, stands out as a notable building of modernist architecture. This academic building, with 1860 square meters spread over two floors, is presented in two offset semicircular blocks connected at the ends, forming a garden in the center. It is characterized by the use of exposed reinforced concrete, glazed panels, and brise-soleil, in addition to promoting natural ventilation through upper louvers made of fixed inclined glass [1,2].

The architectural project of the CDS details an efficient roofing system, designed to manage rainwater - from collection to drainage - in order to ensure the integrity and longevity of the building, in accordance with Brazilian standards NBR 9575 [3] and NBR 15575-5 [4]. This flat roof is made up of a solid concrete slab, a leveling layer with a minimum slope of 1% for drainage, drip edges in embedded galvanized sheet, a waterproofing layer of asphaltic membrane, and a mechanical protection layer of mortar.

In terms of management and drainage, the configuration of the roof directs the flow of rainwater to the ends of the mechanical protection, where it falls freely into a drainage channel located next to the first floor (Figure 1). However, this solution is integrated with other details and specifications in the architectural design in order to ensure the required watertightness and prevent damage and anomalies.

This applies to the construction detail of the drips, which are installed all around the perimeter of the roof - both on the inside and outside edges (Figure 2). Made of galvanized steel sheets (fragmented into rectilinear segments to adapt to the semicircular shape), they are inserted between the regularization layer of the concrete slab and the mechanical protection of the waterproofing, under the asphalt blanket, in order to guarantee their efficiency and prevent their attachment points on the slab from becoming possible points of water percolation and infiltration.

Another solution that appears are friezes (small indentations at the bottom edge of the slabs), as well as slopes on intermediate eaves and marquees. These perform the function of a second gutter and redirect the flow of rainwater in the event of galvanized sheeting malfunctioning or even splashes caused by the action of winds during rain events - thus protecting the frames of circular façades.

The floor gutters (with an independent structure and sloping towards the collection drains) are waterproofed to prevent trapped moisture from rainwater collection from compromising their integrity. On the other hand, the reuse of gray water for garden irrigation, after treatment in its own plant, has not been implemented - despite being planned and dimensioned in the project.

The waterproofing plan (Figure 3) presents recommendations for the execution of the roofing system, including the mechanical protection sheets defined based on the slope diagram (with the watershed at the center) and the expansion joints in positions coinciding with the structural joints. Another specification is the arrangement of asphalt membrane strips, overlapped in the transverse direction and following the curvature of the building, in order to prevent the return or percolation of water through the joints.

Thus, the constructive solution developed for the drainage system, which involves all the elements that make it up, in addition to intercepting and moving the rainwater away from the façades, was designed to dispense with the need for traditional drainage pipes and tubes which, in areas with intense tree planting (as is the case with the UnB building park) are constantly obstructed by vegetation [1,2].

The concern for watertightness, however, continues to be the main feature of both the architectural concept of the Sustainable Development Center and the future interventions carried out in this building. Recently, the University of Brasília approved the installation of photovoltaic panels on the roof to generate clean electricity to be consumed by the department. And, to avoid perforating the mechanical protection during the fixing of the panels, the implemented solution was to fix the metal profiles’ brackets with nuts, washers, and bolts onto concrete blocks set with mortar on the mechanical protection layer. The proposed detail can be seen in Figure 4.

Among the systems that make up the envelope, the roof performs important functions in buildings and directly interferes with the durability of the elements that make it up [4]. Morgado et al. [5] define that a significant portion of the pathologies associated with flat roofs are due to deficient detailing in the design phase, errors in technical execution, inadequate or non-existent maintenance, and exposure to adverse conditions. Facades, functioning as a protective shell of buildings against environmental conditions, end up being, consequently, more exposed to these and, therefore, more susceptible to deterioration [6], especially the roofing.

In this sense, conducting regular building inspections is crucial for monitoring the state of conservation of the building, as well as planning necessary interventions to its good performance and that prolong its service life [7]. In recent years, the use of image acquisition technologies - especially drones - has enabled improvements in inspections and data collection, as well as contributing to decision-making.

Damage maps are graphical tools that aid in understanding the current state of deterioration of the building, as well as the choice of appropriate repair or intervention methods for each type of recognized damage. They represent the relationships between the agents that cause degradation of the construction elements and their respective causes over time, allowing the physical recording of the evolutionary state of conservation [8,9].

In this context, the objective of this article is to evaluate the state of conservation of the flat roof, its elements, and components, investigating the impact of the shape, construction procedures, agents, and active degradation mechanisms, through the conduct of building inspection and the elaboration of qualitative damage maps. The evaluation of the state of conservation contributes to the planning of strategies and actions for preventive and corrective maintenance, considering efficient solutions for the repair of pathologies, extending the service life of the construction systems, and preserving the architectural attributes of the building.

2. Materials and Methods

Conceptually, a damage map is a detailed graphical representation document that surveys all existing and identified damages in a building [9]. It is a tool of great importance during the maintenance and conservation actions of buildings because it visually and simply represents the synthesis of existing pathologies, leaving no room for different interpretations associated with the type of damage. The use of graphic symbols associated with pathologies clearly indicates what was seen during the inspection, provided there is good foundation and description in the captions [10].

There are few studies on pathology mapping from digital photogrammetry, whether of facades or roofs of buildings [6,9]. This is due to the difficulty of acquiring equipment and software, which still have a high cost, limiting the application of the methodology. However, the richness of details in the damage maps is only possible thanks to the use of digital technologies, especially aerial photogrammetry, which allows for inspections with high-resolution image capture from unmanned aerial vehicles (UAV or drone) quickly, safely, and accurately. The cost reduction associated with conducting building inspections should be taken into account [6,11].

The aero photogrammetry method using drones is frequently applied in the inspection of facades due to the difficulty of conducting a visual inspection with the naked eye, without the need for the assembly of support infrastructure, such as scaffolding, ladders, or swing stages. Photogrammetry allows the representation of the actual effective shape of the building’s facades or its roof, as in this case study, since the shape is constructed from photographs that portray the characteristics of the materials at the moment the image is taken [12].

In general, the inspection consists of taking several images of the plan under study, which will be digitally processed through software to construct an orthoimage – the union of the various photos into a single image, generally through the stereo matching method. Considering the dimensions of the building under study, this was the procedure applied for mapping the damages on the roof (Figure 5), which are the orthoimages obtained after processing in software.

Based on the explained process, the following is a case study with the application of the methodology for the production of damage maps from images acquired by aero photogrammetry with a drone applied to the flat roof of the CDS/UnB.

This qualitative study is outlined in the following stages: (i) building inspection and field survey through aerial photogrammetry using a drone; (ii) creation of damage maps in vector representation software; and (iii) assessment of anomalies through identification of the causes, agents, and mechanisms of degradation at work.

The use of a drone (DJI^® Mavic Air 2S model) for the roof inspection was considered to reduce the safety risks associated with inspectors (since the building has no parapet). In addition, the technique allows obtaining high-definition images, whose processing allows greater accuracy in mapping pathological manifestations [13,14,15].

Such images were captured in two distinct periods, under different weather conditions: the first orthoimage, taken at the end of the rainy season, on February 16, 2023, was captured at a height of 56 meters relative to ground level (at a distance of 49 meters from the roof). The second orthoimage, taken at the beginning of the dry season, on May 15, 2023, was obtained at a height of 45 meters from the ground (approximately 38 meters from the roof). The choice of these periods is justified by the possibility of assessing the effects of humidity and temperature variation on the state of conservation of the building’s flat roof.

For the creation of the damage maps, the drawing software AutoCAD^® was chosen due to its ease of handling, interactive interface, and its widespread use by designers and professionals involved in conservation. Regarding the graphic representation of pathological manifestations, the standards developed by Carvalho [16] for damages in reinforced concrete structures were incorporated here, with certain adaptations, as indicated in Table 1.

It’s worth noting that the graphical representation adopted in the construction of the maps disregards any type of color scale associated with the severity level that each pathology represents. Thus, for methodological reasons, it was decided to use colors that best contrasted with the color of the concrete roof surface due to the use of a background image with the real textures of the building’s roof.

So as to facilitate the reading and understanding of each pathological manifestation affecting the flat roof system of the Sustainable Development Center – including its shape, size, and extent – it was decided to create two damage maps. This approach aimed to demonstrate the graphing of the main anomalies clearly recognized in the two orthoimages obtained with the drone, also allowing for the selective association of the data presented in each of the maps [10].

Finally, to complement the diagnosis, an inspection of the roof was conducted by the inspector, for the photographic recording of the existing pathologies, anchored in the visual identification method defined in the Brazilian standard for building inspection [7].

3. Results

Based on the defined methodology, damage maps were created that graphically represent the pathologies expressed in Table 1, in terms of area and extent of damages, identified on the building’s roof. These were produced from the graphical overlay of the obtained orthoimages, which occur, above all, in the layer of mechanical protection of the waterproofing.

Figure 6 shows the damage map constructed from an orthoimage captured with the drone at the end of the rainy period. It identifies the main stains affecting the roofing system, with emphasis on soiling stains from particle deposition and differential washing, as well as moisture stains resulting from the accumulation of rainwater due to problems in directing the flow.

The lighter-colored stains, from the center to the edges, across the entire extent of the roof, are those caused by the carrying of dirt, while the darker-colored stains, which deposit along the edges of the curves that shape the building, signal points of moisture retention.

The damage map in Figure 7, developed from an orthoimage captured with the drone at the beginning of the dry period, shows anomalies identified as cracks, spallings, and stains from biological attacks.

Among the cracks, transversal cracks from one edge to the other, longitudinal cracks next to the water divider (ridge), and cracks distributed along the edges of the mechanical protection, in both the inner and outer curves, stand out.

Spalling generally occurs alongside cracks and at the edges of the flat roof, in sections where hygrothermal variation causes tensions that break the mechanical protection layer. Biological attack occurs near existing trees and results from the decomposition of organic matter (leaves and small branches) that deposit on the surface of the mechanical protection, in a moist and shaded environment.

The association or overlay of the damage maps from Figure 4 and Figure 5 can also assist in diagnosing internal pathologies of the building, such as infiltration points and efflorescence stains, identified mainly in certain sections of the upper floor’s plaster ceiling and in the intermediate slabs connecting the blocks. These pathologies denote the rupture of the waterproofing membrane and water penetration through the cracks defined by the cracks, indicating more severe damage.

Table 2 gathers the main pathologies identified during the in loco inspection, as well as the relationship between the possible causes, agents, and mechanisms of degradation at work.

4. Discussion

The extent, shape, and dimensions of the soiling and moisture stains recognized in the damage map indicate that, in certain sections, the runoff and drainage of rainwater occur as anticipated in the project, as it is possible to identify, through the uniform stains, the path taken from the ridge towards the drip edges at the ends of the flat roof.

On the other hand, the configurations of the moisture stains, with dark coloring, irregular shape, and concentrated along the edges of the blocks, point to deficiencies in runoff and moisture retention which, if not corrected, can lead to water percolation and infiltration problems. Observing the configuration of the stains, it is noted that the runoff of rainwater begins to follow the semicircular shape of the building, moving according to the irregularities of the surface.

The damage map also indicates that the transversal cracks at the ends of the mechanical protection follow a certain frequency and rhythm, since the spacing, length, and thickness are more or less uniform. Being located between the straight segments that form the curvature of the building, always at the change of direction of the panels, their occurrence is related not only to the effects of hygrothermal variation but also to the different movements due to geometry, which tend to open or expand in a non-linear way structures with circular/semicircular shape. Another possible cause is the differential expansion between the mechanical protection mortar and the galvanized drip sheet along the perimeter of the roof, whose tensions can lead to spalling.

In instances where transversal cracks extend from one edge to the other, strategically situated roughly at the midpoint of the span delineated by the building’s structural expansion joints, their specific arrangement, thickness, and occurrence provide insights into the operational behavior of the structure. This phenomenon appears to be an effort to effectively divide the roof into smaller, more manageable panels. The purpose behind this segmentation is likely aimed at mitigating stress and enhancing the overall stability and integrity of the roofing system, thereby accommodating natural movements and adjustments within the building’s framework.

The mechanical protection layer contains only four expansion joints, which align with the building’s structural expansion joints. This configuration leads to tension from hygrothermal variations, causing shifts in the mechanical protection layer and damage to the waterproofing membrane. The presence of moisture stains on the gypsum ceiling below indicates where the membrane has broken in some sections.

Other cracks are also identified in the sections corresponding to the water dividers and close to the structural expansion joints of the building. The presence of dark stains signals water percolation through the cracks, making the roofing system susceptible to moisture and the deleterious action of fluids. This finding reinforces the need for proper sizing of expansion joints, both in the slab and in the mechanical protection layer, to combine the tensions from structural movement due to hygrothermal variation, thus reducing the risk of cracking.

Despite its potential benefits, this approach remains uncommon in waterproofing projects. This is primarily because the Brazilian standard ABNT NBR 9575:2010, while advising the incorporation of expansion joints within the mechanical protection layer, falls short of detailing the specific dimensions that should be implemented. As a result, the absence of clear sizing guidelines within this standard leads to hesitation and variability in the application of such critical structural elements in waterproofing endeavors, underscoring the need for more precise directives to enhance the effectiveness and reliability of these projects.

Knowledge about the pathologies that compromise the state of conservation of the flat roof and consequently endanger its integrity has come to be considered and incorporated, especially when analyzing future interventions in this building. This is the case with the detailing proposed for the installation of photovoltaic panels, recently approved and executed by the university, which sought to avoid perforations on the waterproofed surface to prevent problems with water percolation and infiltration. The solution reveals that the concern for watertightness continues to be a central feature of the architectural design of the Sustainable Development Center, as well as the conservation and maintenance actions of this building.

Finally, the methodological procedures adopted for field survey and elaboration of damage maps, given the safety, accuracy, ease, and speed they represent, can be easily applied for the periodic assessment of the conservation state of flat roofs of other buildings. Moreover, monitoring pathologies can assist in planning corrective or preventive maintenance actions that extend the building’s useful life. The most costly administrative resource will depend only on the acquisition of roof images with the drone, a service that is already outsourced and offered by various companies in the market, but can also be performed by the university itself, through the acquisition of equipment and training of its technical professionals.

5. Conclusions

The design of buildings with a circular/semicircular plan demands special attention regarding watertightness, given the influence of the architectural shape on the direction of rainwater, in addition to the tensions and structural efforts inherent to its geometry.

The elaboration of damage maps of the building’s roof, using aero photogrammetry with drones in vector drawing software, allows for greater agility in monitoring anomalies, enabling high-definition visualization of pathologies and the performance of preventive or corrective maintenance interventions quickly, precisely, and assertively, in order to preserve the intrinsic characteristics of the building.

The case study of the Sustainable Development Center at the University of Brasília highlights the importance of the mechanical protection layer for the good performance of the waterproofing system, reducing pathologies that compromise the structural integrity of the flat roof and the interior of the building. However, its effectiveness will depend on the correct sizing of expansion joints and the characteristics of the applied material, as it is the constructive element most exposed to environmental conditions.

Lastly, through the analysis by overlaying different damage maps, monitoring is facilitated to ease the understanding of associations and cause-and-effect relationships between different damages caused by pathologies over the aging of the building.

Funding

This research received no external funding.

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author/s.

Acknowledgments

Thanks to the Brazilian National Council of Technological and Scientific Development - CNPq and the Coordination for the Improvement of Higher Education Personnel - PROAP/CAPES for financial support. To the Laboratory of Sustainability Applied to Architecture and Urbanism - LaSUS/UnB, for providing drones to obtain images of the roof. To the Infrastructure Secretariat - INFRA/UnB and the Oscar Niemeyer Planning Center - CEPLAN/UnB for technical support and documentary data.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results. This article is a revised and expanded version of a paper entitled ‘Architectural form and state of conservation: a case study from damage maps using drone’, which was presented at XX International Conference on Building Pathology and Constructions Repair – CINPAR 2024, Fortaleza, Brazil.

References

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Figure 1. Schematic section of the CDS/UnB: rainwater flow from the roof (highlighting the drip edges). Source: Oscar Niemeyer Planning Center - CEPLAN/UnB (adapted by the authors).

Figure 2. As built detailing of the CDS/UnB drip edges, made of galvanized steelsheets [1,2].

Figure 3. Executive roof waterproofing project and drainage diagram [1].

Figure 4. Fixing the photovoltaic panels to the roof: (a) Construction detail (Authors, 2024); (b) Execution photo [1]. .

Figure 5. Illustration of taking a single aerial photo with the use of a drone for the representation of the roof plan of the CDS/UnB [1].

Figure 6. Damage map of the roof of the Sustainable Development Center: highlighting soiling and moisture stains [1].

Figure 7. Damage map of the roof of the Sustainable Development Center: highlighting cracks, spallings, and stains from biological attack [1].

Table 1. Graphic representation standards of pathologies [1], adapted from Carvalho [16].

Phatological manifestation	Graphic representation	Simbology
Crack	Linear representation
Spalling	Hatching formed from geometric repetition, in concentric polygons of varied sizes, outlining the area of the pathological manifestation
Biological attack	Hatching formed by point symbols
Soiling and moisture stain	Hatching formed by point symbols

Table 2. Summary Table: Pathological Manifestations and Cause-Effect Relationships [1].

Pathological manifestation	Commentary	Photo
Soiling and moisture stains	Resulting from the carrying of dust particles and/or pollution adhered to the surface by the action of rainwater or the punctual retention of moisture due to drainage deficiencies and technical execution errors, which result in the presence of mold fungi and dark stains across the entire extent of the roof, especially in the final portion of the curves that shape the building.
Transversal cracks from one end to another	Hygrothermal variation combined with a limited number of expansion joints leads to significant structural movement stresses, causing transversal cracks in the mechanical protection mortar, which span from one end of the building to the other. This occurs in an attempt to subdivide the mechanical protection layers of the roof.
Rhythmic transversal cracks (inner curve and outer curve)	Throughout the building’s perimeter, at the ends of the mechanical protection, transversal cracks with regular length, thickness, and spacing are identified along the internal and external curves, especially at the changes in direction of the surface. The presence of dark stains near these cracks indicates susceptibility to infiltration.
Spallings	The stresses arising from structural expansion due to hygrothermal variation reach such intensity in some sections that they are capable of causing displacement of the mechanical protection layer and rupture of the waterproofing membrane, as indicated by the infiltration and moisture stains found in the gypsum ceiling (roof) of the upper floor.
Biological attack	Due to its location in a region of intense tree coverage, some leaves that settle on the mechanical protection layer in shaded areas and with localized moisture retention end up promoting biological colonization and the development of molds, mosses, and vegetation.

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