Technical control activities in waterproofing systems of flat roofs

Transcription

1 Technical control activities in waterproofing systems of flat roofs Fábio Luís Arruda Fagundes Abstract Flat roof systems have associated with them several anomalies related to their waterproofing system which may end up causing leaks into the buildings, leading to a series of problems for the user of the building. Following that feeling of dissatisfaction by the user of the building, urges the adoption of measures aimed at improving the quality of construction. Among those measures are the technical control activities already widely discussed and applied in several countries. Those activities help to promote a higher level of quality of the built environment in general, through an analysis and control of the situations which may cause a decrease of the quality level from the design phase to the implementation phase, and eventually the maintenance phase. Technical control can also serve as a basis for entry into scene of insurers that will define insurance premiums based on the conclusions made by the technical control activities, allowing the user of the building to have an extra guarantee. This work aims to promote the technical control activity, especially the technical control activities of waterproofing systems of flat roofs. The work dealt with the various critical points waterproofing systems of flat roofs and created proposals for improving the reporting models already used for carrying out technical control checks. The present work also includes the application of those proposed models on two study cases. Keywords: Technical control, quality in construction, waterproofing systems, flat roofs, insurances. 1

2 Introduction Waterproofing systems of flat roofs have associated a certain image of distrust due to the series of anomalies related to them. Since those flat roof systems have a lot of components to consider, different types of utilization and specific singular points due the presence of different equipments or constructive details, anomalies can have multiple sources and can have their origin in different phases of the construction, especially in the design, implementation and maintenance phase. In order to face that distrust towards the solution of flat roofs, measures that can offer an extra guarantee to the quality of the constructive system are needed. In this scenario emerges the activity of technical control, which will allow a greater level of construction quality and also can serve as a basis for insurance companies to define insurance premiums, which will ensure a special guarantee for a certain period of time for the owner of the building. Technical control The concept Technical control is a tool that analyses the technical risk associated with the constructive solution, allowing the increase of the construction quality through the control of those risks and assisting the designer and/or the constructor decreasing the associated technical risk by suggesting less anomalyrelated solutions, or by recommending better known solutions. The analysis features a verification of the basic regulations to be applied to the constructive system, which will define the minimum quality level to be expected, and also will proceed to verify if the chosen solution have a sufficient level of knowledge by the local appliers in order to avoid creating a new risk. The final product of a technical control analysis should be a report in which specific activities taken as critical activities - are verified and records are made, and then at the end those records are evaluated and the level of technical risk defined. The technical risk level in this work follows an approach that has been applied in other works made in the recent years in our university which defines three levels for the technical risk: Normal, Aggravated and Very aggravated. 2

3 Building supervision versus technical control Contrary to the activity of building supervision, technical control activity performs a third-party analysis independent relatively to the other entities involved. Also building supervision analyzes the phase of implementation, while technical control, as said before, analyzes the design phase as well. In the phase of implementation (which both activities coincide), the activity of technical control should be less intensive than the building supervision; while building supervision should control most of the implementation aspects on a daily basis, technical control chooses specific days where activities taken as critical are to be performed and analyzes those activities on those chosen days. Technical control can also use the data resulting from the building supervision activity as an extra element to verify if there was a quality environment in the construction site. Technical control organisms and insurance companies Although the aim of technical control it s not only to serve as a basis for the determination of the insurance premiums, that s an unquestionable important goal; therefore the activity of technical control requires an independent and specialized organism to carry on the technical risk analysis. Technical control organisms and insurance companies are different entities and have different goals in the process of setting insurance premiums but at the end they will have complementary tasks. While the technical control organisms will evaluate and define the technical risk associated with the analyzed constructive system, the insurance company will pick up those risk evaluation reports and set the value of the insurance premiums. Different countries and different technical control organisms within a country may have different models of reports for the technical control analysis; this work will approach the Spanish model, which has been applied for some years in Spain and in the recent years in Portugal too. Current application in Portugal and in Europe In some countries in Europe it is required by law to have insurance relatively to the structural elements of the buildings; since those insurances are calculated based on the technical risk established by the technical control analysis, it makes the activity of technical control quite common on those countries. In Portugal it s not obligatory by law to have an insurance relatively to any parts of the building, so the activity of technical control it s only applied when the owner of the building requires an insurance as an extra guarantee. 3

4 The entities that work on this field in Portugal (technical control organisms and insurance companies), are foreign companies that have established themselves in Portugal and apply the knowledge obtained in other countries. The Spanish report model The Spanish report model is a set of 23 reports (the total number can vary) that allows the technical control organism to analyze almost every possible aspect of a building in a standard report, form the design to the execution phase and also includes some analyzes to be done at the end of the construction works. On Table 1 are represented the 23 reports of the model according to Almeida (2011). Code Title D0 Risk definition - Technical risk analysis D01 Structural design review D02 Waterproofing design review D03 Secondary construction works design review D04 Installations design review D1.1 Special work units (foundations) D1.2 Special work units (prefabricated structures) D1.3 Special work units (Facades) D2 Non-traditional materials and systems D3 Waterproofing final report D3bis Waterproofing final report (II) D4 Pre-existing - New construction works over old building D5.1 Foundations execution D5.2 Structure implementation D5.3 Facade and roof implementation D5.4 Secondary construction works implementation D5.5 Installations implementation D6 Works closure D7 Incidences D8 Secondary construction works and installations closure D8bis Secondary construction works and installations closure (II) D9.n Damage repair D10.n Others Table 1 - Spanish report model From those 23 reports, only two of them deal directly with the waterproofing system of flat roofs: report D02: Waterproofing design review and report D3: Waterproofing final report. 4

5 Report D02 deals with the design phase; verifies if the regulation have been followed, if the designed roof system is correctly specified according to its future use and also checks if enough data regarding the maintenance of the flat roof system are being compiled in the Building s book. Also report D02 should analyze possible incompatibilities between the system components (chemical, thermic due the installation of membranes, etc) and if there is enough design data especially on singular points (such as movement joints, points where the roofing membrane face a wall, a doorstep, etc). Report D3 handles with the implementation phase; the most important verification of this report is to analyze if in fact, the design specifications are being correctly implemented in the construction site. Also tries to evaluate if the materials are being correctly handled and applied (certain types of membranes need to have a few cautions regarding its storing per example), but this task to be perfectly done would need a more active control of the building site, which is not the aim of technical control as already approached on the comparison between the building supervision activity versus the technical control. Another report from the Spanish model could be used in the ambit of waterproofing systems of flat roofs: the D3bis report. This report is used at the end of the insurance guarantee time (usually three years), in order to extend that time, or in cases of some kind of modification during that time. Since it is optional, no further reference will be made to this document in this work. Waterproofing systems of flat roofs Introducing the constructive system Flat roofs solutions have been gaining some room in nowadays constructions due the several advantages related to them, such as accompanying architectonic movements and the creation of an extra space in the buildings in which many uses can be considered. Also the technical improvements related to their components made in the recent past have granted to the flat roof systems a better performance facing the basic requirements specified in the regulation 305/2011 by the UE. Waterproofing systems of flat roofs are a fundamental component of the constructive system because they guarantee by themselves that no water from an outside source will go through the roof, if correctly done. To achieve that goal whit a good associated quality level a certain number of system components should be considered and correctly applied. Those system components and its characteristics may vary according with the type of utilization the flat roof will have. 5

6 System components The main flat roof system components, present in every type of flat roof independently of its use, are the roof slab, the support of the membrane (which may be the shape layer or the thermal insulation), the roofing membrane and its protection. Those components and their main functions are presented in Table 2. Component Roof slab Insulation Shape layer Roofing membrane Roofing membrane protection Function Provides the necessary mechanic resistance to the solicitations of the roof Lowers the exchanges of heat between the inside and outside; can serve as a support to the roofing membrane Provides the necessary slope to the flat roof system; can serve as a support to the roofing membrane Turns the flat roof waterproof Protects the roofing membrane from atmospheric and mechanic actions Table 2 - Main components of flat roof systems and their functions Besides those components referred above there are a few that should be considered such as the vapor control layer, regularization layer and a layer capable of spreading the tensions due to the mechanic actions on the roof separator. Also some types of materials contacting the roofing membrane can be chemically incompatible or in those cases where the application of the roofing membrane requires a source of heat which may damage the materials of the support, a layer to serve as a thermal barrier should be implemented. Other components could be considered depending on the use foreseen for the flat roof such as a heavy protection for the roofing membrane (which can vary from gravel to concrete), filter sheet and drainage membrane (this last two for roof gardens). Types of utilization for the flat roofs Different types of use will generate different solicitations to the flat roof system and that s an important aspect to consider while designing a flat roof or analyzing a design of a flat roof. In this work, in an approach similar to what have been in the past years in Portugal, four main types have been considered, plus another one that can occur as a variant. Table 3 resumes the types of utilization considered on this work. 6

7 Type of utilization Not accessible flat roof People accessible flat roof Vehicles accessible flat roof Roof garden Variants Characteristics Only maintenance works considered; protection to the atmospheric agents may be needed. The protection of the waterproofing membrane should avoid damage related to the actions originated by the presence of people. The protection of the waterproofing membrane should take into account the increment of the mechanic actions caused by the presence of cars. In this type of utilization, protection to the roots as well as a filter sheet and a drainage membrane should be applied to avoid damages related to the roots and to the excess of water that may accumulate in the soil. In this item it is considered those cases where the thermal insulation varies from its most traditional place in the flat roof. Important for rehabilitation cases. Table 3 - Types of utilization of flat roofs As mentioned in Table 3, different types of utilization will require different components with different characteristics, and also another kind of item to be analyzed by the technical control, because if the correct components aren t applied, anomalies may be generated which will make the quality level to drop. Roofing membranes The roofing membranes approached in this work are the ones more commonly used nowadays in Portugal: modified bitumen membranes (with APP and SBS polymer) and thermoplastic PVC membranes. The modified bitumen membranes are generally applied in a heat process in which the seams are heated to melt the asphalt together and create a seal. This process may require a heat barrier if the support of the membrane is affected by heat. Thermoplastic PVC membranes are generally applied on the roof without a continuous bonding to the support. The lap seams are melted with heat (most common), and a certain weight must be place on top of the membrane to avoid wind related anomalies. Also this type of membranes is usually chemically incompatible with a few kinds of thermal insulation (for example the most commonly used in flat roof systems: expanded and extruded polystyrene). 7

8 To summarize the text above in the technical control point of view, different solutions of roofing membranes will imply different verifications to be done regarding compatibilities and bonding characteristics. Roofing membranes in singular points Some zones of the flat roof require a special attention regarding the application of the roofing membrane. In this work four types of these points have been indentified and general solutions for those have been proposed according to different studies and recommendations. The four types of singular points are shown in Table 4, it their general aspects that should be considered. Singular point Flat roof to wall intersection General aspects There's a minimum height of 0,10 m that should be applied to the part of the membrane on the wall. It's important to separate the membrane on the wall from the membrane on the roof. Movement joint Rainwater drainage and evacuation points Flat roof to circular elements intersection The roof membrane should only go near the joint and another piece of membrane over it. A flexible material should be placed on the joint; that will serve as a support for the piece of membrane that covers the joint. The membrane applied on the drainage parts of the roof should be applied upward in the flat roof. Like the flat roof facing the wall there's a minimum height to be considered to the membrane applied on the element (different piece from the one applied on the roof surface). Table 4 - Singular points approached As it can be seen by the resume presented in Table 4, those singular points have a lot of aspects to be considered on the design phase and thereby its analysis by the technical control activity is very important. Anomalies in waterproofing systems of flat roofs The study of the anomalies that may occur on flat roofs presented in this work was based on a study done by Silva (2001). In this extended abstract, doesn t make sense to refer the anomalies and its causes but presenting some data related to where they usually occur and in which phase helps to understand the impact that the activity of technical control can have and in which parts of the flat roof. 8

9 In Figure 1 there s a graphic indicating in which phase those anomalies occurred on the study mentioned before. Phases of the anomalies 10% 44% 8% 38% Design Implementation Materials Utilization Figure 1 - Phases of the anomalies On Figure 2, the locations of those anomalies are presented (according to the same study). Locations of the anomalies 21% 13% 38% 28% Roof surface Peripheral zones Rainwater evacuation dispositives Other singular points Figure 2 Locations of the anomalies According to Figure 1, and as expected, the design and implementation phases have a massive importance for the quality of the constructive system and if the quality of those phases is assured only 18% of the detected anomalies would still occur. Figure 2 on its turn, shows that singular points have a big significance in the final quality of the flat roof. By joining the analysis made on those two figures, we could easily conclude that an efficient 9

10 technical control analysis would have great focus on the design phase, especially on the singular points; on the other hand in the implementation phase it s important to verify if what has been done is according to the design. Proposal to the Spanish model After the study made to the constructive system approached and to the currently used reports of the Spanish model, a proposal was made trying to improve the model; to each type of singular points was created an annex, checking if the general good concepts were being applied in the design phase. To the roof surface was also created an annex that would deal with the fixation system, the slope scheme, the type of utilization and others. On the main part of the report for the design phase was modified the point related to the singular points, requiring the existence of design details for all existing points; also the creation of the book of the building has been introduced. On the implementation report, not much has been modified since the technical control activities on that phase consist mostly in verifying if the design are being correctly implemented. Since those reports consist in a check-list format, even though they may have gotten a bit extended, they are still quickly completed. References Almeida, Nuno Gonçalo Cordeiro Marques de Modelo de Gestão Técnica de Edifícios Baseada no Desempenho e no Risco - Conceção, desenvolvimento e exemplo de aplicação a estruturas. Lisboa : IST, Silva, José Mendes da e Gonçalves, Pedro Patologias Frequentes em Coberturas Planas em Portugal. Lisboa : IST, Congresso Nacional da Construção. 10