Restoration of the Army built heritage. Flat roofs rehabilitation and technology of Army buildings

Transcription

1 Restoration of the Army built heritage. Flat roofs rehabilitation and technology of Army buildings Bruno João Fernandes Poça Military Engineering Integrated Masters Supervisor: Dr. Jorge Manuel Caliço Lopes de Brito Co-Supervisor: Dr. Inês dos Santos Flores Barbosa Colen October 2015

2 1. Introduction A roof consists of a set of load-bearing and protective elements that intend to protect the interior of buildings from meteorological phenomena such as rain, heat, cold, wind and snow, sheltering the building's structure and ensuring high standards of living conditions [1]. In Portugal, according to data from the National Institute of Statistics (INE) the ratio of flat roofs to pitched roofs has been steadily increasing and between 2006 and 2011 the use of mixed and flat roofs represented 12.5% of those used in Portugal. Therefore, and given the increased importance of these structures, it is necessary to create a system that supports the repair of anomalous situations in roofs operation [2]. As flat roofs are practically horizontal, special care is needed when choosing and positioning materials, as well as when evaluating the behaviour of the assembly in situ. When anomalies that can affect the correct operation of a roof occur, diagnosis techniques are used to locate the origin of the anomaly so as to be able to evaluate the most adequate intervention technique and repair the structure. 2. Technology A flat roof is considered to be one in which its materials are positioned horizontally or close to it. In reality, according to the General Regulation for Urban Building (RGEU) the roof must have a minimum slope of 1%. In the specific case of social housing, the Technical Recommendations for Social Housing (RTHS) state that the minimum slope should be 2%. The upper limit of the slope for a roof to be considered flat is around 8%. This value changes depending on the country and existing legislation [3, 4]. The flat roof essentially consists of the following elements: a load-bearing structure, a shaping layer, thermal insulation, a waterproofing layer and a protective layer. It may also include a smoothing layer, a vapour barrier and a separation layer Functional requirements The functional requirements apply not only to the roof as a whole but also to its individual components. Generally, flat roofs comply with the general directives of the European Union for Technical Approval (UEAtc) and fall under the following quality categories: safety requirements, housing requirements, durability, construction and functionality requirements. The requirements for the waterproofing materials are part of the following categories: safety requirements, conservation, maintenance, repair and use requirements [6-11] Roof classification The main aspects to be considered, according to the authors [3, 5], when designing and executing flat roofs can be classified as: accessibility; waterproofing layer; the type of coating used in the waterproofing layer; the positioning of the thermal insulation relative to the waterproofing; the slope; the load-bearing structure. Dissertation for the Integrated Masters in Military Engineering 1

3 Classification of the accessibility Taking into account the type of use, flat roofs can be classified as accessible, non-accessible or special [3, 5]. Non-accessible roofs are those thawhoset access is restricted to maintenance or repair whilst accessible roofs allow people to circulate and remain on them. Accessible roofs may not only be accessed to people but also to vehicles, like in car parks. Examples of special roofs are industrial roofs, green roofs, etc Classification of the waterproofing layer The purpose of the waterproofing layer is to protect other elements from ultraviolet radiation as well as surface wear. Heavy protection, as well as satisfying these requirements also has enough weight to ensure that other elements are not dragged by the wind. The type of protection applied to the waterproofing layer (or the absence thereof) comprises three categories: roofs with no protection, light protection, and heavy protection [3, 5] Classification of the types of waterproofing layers Waterproofing layers can be classified as traditional or non-traditional [3]. Traditional waterproofing is the one most currently used and well known in construction. Non-traditional waterproofing, on the other hand, is more recent and its performance on site is not as well known Classification of the positioning of the thermal insulation layer The positioning of the thermal layer relative to the waterproofing layer can be classified as traditional or inverted [3]. The traditional system has its thermal insulation underneath the waterproofing layer. The waterproofing layer of this system suffers greater wear given that it is exposed to: differential temperature variations (both daily and seasonal); mechanical damage, especially during the construction process; degradation due to ultraviolet radiation; degradation caused by humidity present on the lower part of the waterproofing layer. In an inverted roof, the thermal insulation layer is located above the waterproofing layer, and it therefore protects the waterproofing layer from the above external factors, leading to greater durability. Figure 1 illustrates a temperature profile for each element of a traditional and an inverted roof. The waterproofing layer of the traditional roof is subject to considerably higher temperature than that of the inverted roof. Depending on the thickness of the thermal insulation, exposure to solar radiation, the season and the type of roof protection, the waterproofing layer of the inverted roof can have up to 50% lower temperatures than when compared to the traditional roof. Traditional Inverted Figure 1 - Temperature profiles of a traditional roof and an inverted roof ( Dissertation for the Integrated Masters in Military Engineering 2

4 Classification of the resistant structure The classification of the roof and its structure is based on how much it deforms, and can be considered flexible or rigid depending on how significant the deformation perpendicular to the roof is. Rigid structures can be further categorised as joint-free or discontinuous (in situations where they are executed using joints) Materials The most currently used waterproofing membranes used in flat roof are bituminous polymers, thermoplastic and elastomeric [12]. Polymer resins are also used not only in waterproofing but also for system repairs. Table 1 summarises the classification of waterproofing materials. Table 1- Classification of the waterproofing system [3, 13] Traditional materiais Application Class of materials Types of materials In situ Bituminous materials Products Direct distilled bitumen Oxidised or inflated bitumen Bitumen emulsions Bitumen paintings Modified bitumen products Pozzolan cement Pre-fabricated Saturated or impregnated reinforcing Bitumen membranes Bitumen screens Bitumen felts Felt reinforcing Screen reinforcing Leaf reinforcing Non-traditional materiais In situ Liquid or paste Polymer modified bitumen emulsions or solutions Water dispersible polymers Heated polymer modified bitumen Non-saturated fibre-glass reinforced polyester resins Flexible non-saturated polyester Polyurethane Mixture of polymeric and cement resins Bituminous polymers APP SBS PVC incompatible with bitumen Pre-fabricated Membranes Thermoplastic PVC compatible with bitumen CPE (chlorate polyethylene) FTO or TPO (flexible thermoplastic polyolefin) Butyl rubber (isopren-isobutilene) Elastomeric EPDM (ethylene-propylene-diene monomer) Chlorosulphonated polyethylene PIB (poli-isobutilene) Dissertation for the Integrated Masters in Military Engineering 3

5 3. Pathology According to various authors, pathology in construction consists of a number of errors of defects, leading to a potential decrease in safety, health, economy, environment or quality of life of the users of the building. Roof anomalies are mostly due to humidity or water infiltration. These are noticeable in the layers underneath the waterproofing layer, and can lead to damages that can be considerable, depending on the amount of repair necessary, and in extreme cases jeopardizing the use of the space. According to [14], the most frequent anomalies in flat roof are classified in Table 2. Table 2 - Classification of flat roof anomalies (Conceição, 2015) Classification of flat roof anomalies General Singularities A-G1 Surface wear A-S1 Inadequate expansion joint s design A-G2 Fracture/failure A-S2 Inadequate downspout s design A-G3 Detachment/peeling A-S3 Inadequate safety tube s design A-G4 Creasing/bulging A-S4 Inadequate lap joints design A-G5 Cracking A-S5 Inadequate gutter s design A-G6 Puncture A-S6 Defects in fastenings A-G7 Absence/inadequate layer s positioning A-S7 Defects in copings A-G8 Debris accumulation A-S8 Defects in tail-ends A-G9 Inadequate slope/ponding A-G10 Biological growth A-G11 Corrosion A-G12 Moisture stains of condensation/infiltration 4. Rehabilitation The rehabilitation process of this type of anomalies can be done either integrally or partially. Integral repair consists in removing all the affected elements, including the lateral ones. However, in cases where the anomaly in the waterproofing system is localised, the repair can also be localised. In these cases, the intervention and repair technique used are generally identical to those used if the anomaly is general. Another intervention solution to ensure the waterproofing of a flat roof is to apply a new constructive system without removing the existing layers. The choice of these alternatives, according to [15, 16], depends on various factors, the most important of which are: the age of the existing waterproofing system; the condition of the system and the roof's layers; compatibility of the materials to be in contact with each other; roof accessibility Classification of the rehabilitation techniques With the objective of re-establishing all of the functional requirements of the flat roof, Table 3 lists the rehabilitation techniques used. Dissertation for the Integrated Masters in Military Engineering 4

6 Rehabilitation technique Table 3 - Classification of the rehabilitation techniques General R.1 Cleaning of the exterior coating of the flat roof R.2 Application/repair/substitution of the waterproofing system R.3 Application/repair/substitution of the thermal insulation R.4 Application/repair/substitution of the separation layer R.5 Application/repair/substitution of the vapour barrier R.6 Application/substitution of the shaping layer R.7 Creation of circulation routes Singularities R.8 Application/repair/substitution of expansion joints R.9 Repair of joints and associated protective elements R.10 Application/repair/substitution of the drainage system R.11 Application/repair/substitution of fastening elements The rehabilitation techniques presented in Table 3 can be classified as curative repair techniques (RC), preventive repair techniques (RP) and/or as maintenance work (M). The definition of each type of repair technique is presented in Table 4 [17]. Table 4 - Types of repair techniques Curative repair (RC) R.1; R.2; R.3; R.4; R.5; R.6; R.8; R.9; R.10; R.11 Preventive repair (RP) R.2; R.3; R.4; R.5; R.7; R.8; R.9; R.10; R.11 Maintenance (M) R.1 The objective of curative repair techniques is to repair, eliminate or hide any given anomaly. Preventive repair techniques seek not only to restore operational characteristics but also to eliminate the cause of the anomaly. Maintenance work consists of a set of interventions that are meant to prevent and on a smaller scale correct anomalies for the element to function correctly and thus enable the flat roof to reach its estimated service life. To select the most appropriate repair technique, whilst taking into account the most economically viable, it is necessary to take into account the following factors: analyse the state of the anomaly; analyse the remaining service life of the other elements that are part of the flat roof; intervention costs according to the estimated value of the element to be repaired; urgency of the intervention; risks to the users; associated client requirements and conditions Cleaning of the exterior coating of the flat roof The cleaning of the exterior coating consists of a repair technique that is applied to the upper side of the roof, and is simultaneously a maintenance and curative repair technique. When using chemical products to eliminate biological colonisation, it is necessary to check that they do not affect the chemical stability of the waterproofing or thermal insulation systems. This repair technique is applied to all the roof and drainage system, and it can be done through brushing, blowers or jet washing. Dissertation for the Integrated Masters in Military Engineering 5

7 Application/repair/substitution of the waterproofing system This technique is considered to be curative and preventive. Before its application, it is necessary to know what caused the changes in the waterproofing system. In the case that the anomaly has spread throughout the roof, the repair technique implies the substitution of the entire system or the application of a new waterproofing system above the pre-existing one. If, however, the anomaly is located in a specific part of the roof, then the repair technique can be localised Application/repair/substitution of the thermal insulation The repair of the thermal insulation is recommended when there is condensation on the lower part of the slab, when the waterproofing system is exposed to thermal variations that reduce its service life, and when it is degraded or has no protection layer. The reinforcement of the thermal insulation can be done: underneath the slab, between the slab and the waterproofing membrane; above the waterproofing membrane Application/repair/substitution of the separation layer This repair technique can be curative and/or preventive. This layer aims to separate the waterproofing coating from the protective layer, contributing towards minimizing the results of negative mechanical actions, as well as enabling water that reaches this layer to be drained Application/repair/substitution of the water vapour barrier The function of the water vapour barrier is to stop water vapour from passing through and avoiding condensation on the interior side of the load-bearing structure. In an inverted roof this specific barrier is not necessary as the waterproofing also serves the purpose of the water vapour barrier Application/substitution of the shaping layer The shaping layer can consist of cellular concrete, Light Expanded Clay Aggregate (LECA) or lightweight concrete using granulated expanded polystyrene. The layer should be applied on dry, clean and smooth supports. When using lightweight concrete, it is crucial to use a screed over the lightweight concrete layer so as to regulate it Creation of circulation routes The creation of routes for circulation on non-accessible roofs is considered to be a preventive repair technique. In the case of a roof with self-protected membranes, the creation of circulation routes implies their reinforcement, as a distinct self-protected membrane of a different colour is used to signal passages. If the protective layer is of gravel or round gravel, the procedure involves placing slabs on the routes Application/repair/substitution of the expansion joints The repair of expansion joints is simultaneously a curative and preventive technique. The treatment of expansion joints should involve using compressible materials, which can absorb the stress caused by the movement of the joints. The waterproofing membranes should be positioned to ensure that they are not under tension if the expansion joints move. Dissertation for the Integrated Masters in Military Engineering 6

8 Repair of joints and associated protective elements The repair of specific points can at times be difficult because the waterproofing systems are of different materials and the space available to work in is often too small. Sometimes it is advantageous and more practical to repair all of the joints using a liquid polyurethane membrane. This solution has a high level of adherence to all types of materials such as bitumen, screed, metallic and wooden elements, and adapts easily to any type of geometry Application/repair/substitution of the drainage system This repair technique is considered to be curative and preventive. It is applied to problems associated to discharge elements, drains, gutters and drainage tubes. To avoid clogging of the drainage system, accessories should be placed at the entrance to stop larger debris entering the drainage tubes. Accessories such as drain nozzles and covers serve this purpose Application/repair/substitution of the fastening elements The technique used to repair fastening elements is both curative and preventive. The technique uses specific parts made of galvanised steel, stainless steel, tempered steel, aluminium or plastic, so as to set the thermal insulation and/or the waterproofing system to the structure. Depending on the way it is connected to the element, the mechanical setting can be designated as linear or localized. In the latter each screw has a distribution element of the tightening force, whilst with the former the fastening element tightens the membrane predominantly in one direction. 5. System validation and statistical treatment of the data The objective of this chapter is to validate the proposed classification system, through the comparison of the theoretical and practical anomalies - rehabilitation techniques matrices, and posterior calibration. The data obtained via the inspection plan were also statistically analysed in depth. The field work consisted of visual inspection of the roofs, supported by knowledge acquired from the consulted literature and from interviews of company staff, with no in situ laboratory trials having been made Validation of the correlation matrix This dissertation proposes a system that aids flat roofs rehabilitation through the use of a theoretical anomalies - repair techniques correlation matrix. With the data obtained from the field work, a comparison between the values obtained from the inspections and the theoretical matrix was made. This analysis enabled the data previously proposed for the inspection plan to be calibrated and ensured that the matrix has a higher degree of reliability. Table 7 illustrates the corrected anomalies - rehabilitation techniques correlation matrix. Green indicates that the theoretical value corresponds to the practical value, and yellow means that the theoretical value was revised upon analysing the practical results. In the intersection between each line (which represents an anomaly) and each column (which represents a rehabilitation technique), a number is introduced that represents the degree of correlation between the anomaly and the rehabilitation technique, according to the criteria defined by [17] and [18], consisting of: Dissertation for the Integrated Masters in Military Engineering 7

9 0 - no correlation: there is no correlation between the anomaly and the repair technique; 1 - small correlation: appropriate repair technique, considering applicability limitations, in repairing the anomaly or eliminating the cause(s) of the anomaly; 2 - large correlation: the most appropriate repair technique to eliminate the anomaly or its cause(s). Table 5 - Corrected anomalies - rehabilitation techniques correlation matrix after the proposed system was calibrated based on the obtained sample Anomalies correlation matrix - rehabilitation techniques A / R R.1 R.2 R.3 R.4 R.5 R.6 R.7 R.8 R.9 R.10 R.11 A-G A-G A-G A-G A-G A-G A-G A-G A-G A-G A-G A-G A-S A-S A-S A-S A-S A-S A-S A-S The sample consists of 105 inspected flat roofs, in which 608 anomalies were identified. For each anomaly, one or more rehabilitation technique was associated, leading to a total of 385 techniques and an average of 1.58 rehabilitation techniques per anomaly. An average value of 1 means that the corrective measures were only related to the repair of the anomaly and did not eliminate its cause. Figure 2 shows that almost the whole sample requires intervention of the type R.1 (cleaning of the exterior coating of the flat roof) and R.2 (application/repair/substitution of the waterproofing system). The need for repair technique R.1 is justified due to the lack of a maintenance plan, be it periodic or regular. Its absence leads to a progressive accumulation of debris and vegetation that compromises, in the short term, the correct operation of the roof. The high use of the repair technique R.2 illustrates the small number of roofs on which the waterproofing is in optimal conditions R.1 R.2 R.3 R.4 R.5 R.6 R.7 R.8 R.9 R.10 R.11 Figure 2 - The absolute frequency of the rehabilitation techniques proposed for the sample Dissertation for the Integrated Masters in Military Engineering 8

10 Figure 3 shows that anomalies A-G8 (debris accumulation), A-G10 (biological colonisation) and A-G1 (superficial wear) are the most common ones, accounting for more than half of the sample. The frequent occurrence of A-G8 was to be expected considering the fast proliferation of biocolonization on roof claddings. The occurrence of both anomaly A-G8 and A-G8 is mainly due to the absence of maintenance plans. On the other hand, anomalies such as A-S3 (inadequate down piping design) and A-S6 (deficient fastening) were far less common. A-G1 A-G2 A-G3 A-G4 A-G5 A-G6 A-G7 A-G8 A-G9 A-G10 A-G11 A-G12 A-S1 A-S2 A-S3 A-S4 A-S5 A-S6 A-S7 A-S8 4% 7% 0% 10% 20% 30% 40% 50% 60% 70% 80% Figure 3 - Relative frequency of each anomaly on the 105 inspected roofs Figure 4 indicates the relative frequency of the adopted rehabilitation techniques as a function of the materials used for waterproofing. Liquid membranes resort less to the R.1 technique (cleaning of the exterior coating of the flat roof) than other waterproofing materials. This result is mainly due to this material not creating favourable conditions for vegetation to grow, meaning there is less need for intervention to remove it. 12% 12% 11% 13% 19% 22% 22% 25% 23% 29% 30% 33% 36% 46% 48% 50% 62% 74% 100% 80% 60% 40% 20% 0% PVC membranes Bitumen membranes Liquid membrane 100% 98% 94% 91% 91% 82% 71% 60% 49% 36% 36% 43% 29% 27% 24% 29% 36% 14% 18% 9% 9% 14% 10% 1% R.1 R.2 R.3 R.4 R.5 R.6 R.7 R.8 R.9 R.10 R.11 1% Figure 4 - Relative frequency of the rehabilitation techniques applied to the different waterproofing materials PVC membranes had 20% less use of technique R.2 (application/repair/substitution of the waterproofing system) than other systems. It also needed around half of the frequency of technique R.9 (repair of joins and protective elements) when compared to bituminous membranes. Dissertation for the Integrated Masters in Military Engineering 9

11 6. Conclusions Contrary to pitched roofs, the use of flat roofs in Portugal has been growing, and 12.5% of buildings built during 2006 and 2s011 have flat roof. The quality and performance of the materials that form a flat roof is only ensured if the correct procedures for construction are followed, and the manufacturer's recommendations, found in chapters 2 and 4, should be complied with. Otherwise anomalies may appear much earlier than is expected in the roofs service life, negatively affecting its operation. The waterproofing membrane of a traditional roof is subjected to higher temperatures than that of an inverted roof. Depending on the thickness of the thermal insulation, exposure to solar radiation, the season and the type of protection, the waterproofing coating of an inverted roof may register temperatures up to 50% less than those of the traditional roof. The repair of an anomaly on a roof should be made by specialised personnel, and prior to this the roof should be inspected so that the most appropriate measures to be implemented are chosen, avoiding unnecessary interventions and expenses. The implementation of this work, as well as that of System for inspecting and diagnosing flat roofs. Restoration of the Army built heritage (Conceição, 2015), consist of innovative tools to aid understanding, inspecting, diagnosing and repairing flat roofs. The main anomalies detected via the inspections are related with debris accumulation (A-G8), biological colonisation (A-G10) and superficial wear (A-G1), accounting for more than 50% of the anomalies. The least common anomalies were the lack of or inadequate design of down piping (A-S3) and the lack of or inadequate design of fastenings (A-S6). The majority of the inspected roofs did not show any sign of having a maintenance plan. This is reinforced by the use of technique R.1 (cleaning of the exterior coating of the roof) present in 93% of the sample, given that the objective of this technique is to correct anomalies such as A-G8 (debris accumulation) and/or A-G10 (biological colonisation). References [1] Gomes, R. Flat roof. Technical information buildings. LNEC, Lisbon, 1968 [2] Census 2011: Definitive results - Portugal. National Statistics Institute (INE), Lisbon, 2012, ISBN (in Portuguese) [3] Lopes, J. G. Flat roof waterproofing coatings. Technical information buildings, ITE 34, Lisbon, 2010 (in Portuguese) [4] Decree-law n.º 38382, 7 August 1951, General Regulation for Urban Building (RGEU). National press - Coin house. Lisbon, 1988 (in Portuguese) [5] Cahier n. º 2662 du CSTB - Guide technique UEAtc pour l agrément des systèmes isolants supports d étanchéité des toitures plates et inclinées, UEAtc. Paris, Juin 1993 (in French) [6] ETAG Guideline for European technical approval of systems of mechanically fastened flexible roof waterproofing membranes. Edition March 2000 Amended November 2012 Dissertation for the Integrated Masters in Military Engineering 10

12 [7] pren Flexible sheets for waterproofing reinforced bitumen sheets for waterproofing. Definitions and characteristics, CEN 2001 [8] pren Flexible sheets for waterproofing. Plastic and rubber sheets for waterproofing. Definitions and characteristics, CEN 2001 [9] Cahier n. º 1812 du CSTB - Directives générales UEAtc pour l agrément des revêtements d étanchéité de toitures, UEAtc. Paris, Novembre 1981(in French) [10] Cahier n. º 2502 du CSTB - Guide technique particulier UEAtc pour l agrément des revêtements d étanchéité de toitures monocouches, UEAtc. Paris, Juin 1991(in French) [11] Cahier n. º 2510 du CSTB - Guide technique complémentaire UEAtc pour l agrément des revêtements d étanchéité de toitures fixés mécaniquement, UEAtc. Paris Juillet - Août 1991 (in French) [12] Gonçalves, M.; Lopes, G.; Brito, J. de; Lopes, M. Characteristics of membrane waterproofing flat roof. Universidade do Minho, Civil Engineering, n. 2, pp , 2005 (in Portuguese) [13] Ginga, D. Flat roof waterproofing systems. Materials, systems and anomalies. Military Engineering Integrated Masters, Instituto Superior Técnico, Lisbon, 2008 (in Portuguese) [14] Conceição, J. System for inspecting and diagnosing flat roof. Restoration of the Army built heritage. Military Engineering Integrated Masters, Instituto Superior Técnico, Lisbon, 2015 (in Portuguese) [15] Paiva, J.; Aguiar, J.; Pinho A. Technical guide for housing rehabilitation. 1st edition. Lisbon, 2006, ISBN (in Portuguese) [16] Figueiredo, J. Survey anomalies in waterproofing flat roof systems. Civil Engineering Integrated Masters, Instituto Superior de Engenharia de Lisbon, 2012 (in Portuguese) [17] Silvestre, J. D. Support system inspection and diagnosis of abnormalities in adhesive tiles. Construction Engineering Integrated Masters, Instituto Superior Técnico, Lisbon, 2005 (in Portuguese) [18] Brito, J. de Development of a management system for concrete buildings. PhD thesis in Civil Engineering, Instituto Superior Técnico, Lisbon, 1992 (in Portuguese) Dissertation for the Integrated Masters in Military Engineering 11