Ebook: COST C16 Improving the Quality of Existing Urban Building Envelopes

In front of you lies one of the four books produced within the scope of Action C16 “Improving the quality of existing urban building envelopes” which started as a COST UCE programme. The acronym ‘COST’ stands for European COoperation in the field of Scientific and Technical research, and falls under the Urban Civil Engineering Technical Committee (UCE). The main characteristic of COST is a ‘bottom-up approach’. The idea and subject of a COST Action comes from the European scientists themselves. Participation is open to all COST countries but only those countries that wish to participate in an Action do so. As a precursor to advanced multidisciplinary research, COST has a very important role in building the European Research area (ERA), anticipating and complementing the activities of the Framework Programmes, acting as a bridge between the scientific communities of emerging countries, increasing the mobility of researchers across Europe and fostering the establishment of large Framework Programme projects in many key scientific domains. It covers both basic and applied or technological research and also addresses issues of a pre-normative nature or of societal importance. The organisation of COST reflects its inter-governmental nature. Key decisions are taken at Ministerial conferences and also delegated to the Committee of Senior Officials (CSO), which is charged with the oversight and strategic development of COST.

The COST Action C16 “Improving the quality of existing urban building envelopes” is directed to multi-storey residential blocks from the period after World War II, especially those built during the period when the need for housing in Europe was at its greatest. That is why the COST Action C16 focussed on the period 1950 to 1980. We found it necessary to propose this Action after the completion of Action C5 “Urban heritage/building maintenance”.

According to studies carried out by Action COST C-5, the estimated value of the European Urban Heritage amounts to about 40 trillion Euro (1998 prices) for the housing stock alone. The same research indicated the differences between the countries of the EU as well as what they have in common. The age profile of the building stock of a country like the Netherlands differs from that of the UK. Of interest too, are the costs of maintenance, renovation and refurbishment of the building stock. For the EU as a whole, this amount is about 1 trillion Euros per year (1998 prices). At the same time the three ‘Building Decay Surveys’ issued by the Federal Government of Germany that were based on systematic, scientific building research projects, indicated that 80% of all building decay is found in urban building envelopes (roof, walls, foundation).

There are elements in the building stock that are common to the countries in Europe. These include:

– Most of the buildings were completed after 1950. For a country like the Netherlands this means 75% of the existing buildings.

– The maintenance costs are mainly incurred in urban building envelopes,

– The renovation of buildings and reconstruction to provide an improved or different range of use will influence the building envelope,

– The quality of the building envelope very often fails to meet current demands and will certainly not meet future demands.

An important conclusion deriving from the points mentioned above is that however important maintenance may be, it does not lead to the desired improvement in the quality of urban building envelopes. Improvement of the quality of urban building envelopes must be the real task. Such improvement requires the development of new and suitable strategies for local authorities, housing corporations and owners and also architects and civil engineers.

Until now integrated engineering aspects have been disregarded in this process. In many European countries new technologies have been developed, but these have either not yet been translated into practice, or have been only locally used to achieve a higher quality in urban buildings. This results in a limited impact on urban environments. Therefore it is essential to bring all kinds of local solutions together, to learn from these and to find a more general approach that can be used for building systems. Often problems and their solutions are approached in isolation. The wish to improve the quality of an individual building envelope usually leads to a local, project-based solution. Solving the specific problems of this renovation-project becomes the sole target. To reach maximum value for money, it is essential to integrate all the factors influencing urban building envelopes and look at them in a broader scope.

As a result of changes in the composition of the population, society continuously changes with respect to various factors including age-structure, family composition and the availability of energy. Changes lead to situations that are reflected in the commissioning of buildings, which is gradually shifting from new construction to the reuse and renovation of existing buildings that often requires the modification of their facades.

Even when buildings may still be functionally satisfactory, there may be external factors, such as the dullness of the image that they summon up or their poor technical quality, that require that attention should be paid to the shell of the building. There are many reasons why buildings may no longer be adequate. Failure to satisfy current demands may be expressed in lack of occupancy and further deterioration of the neighbourhood. This establishes a vicious circle, which can and must be broken. All too quickly discussions turn to demolition and new development, without prior investigation of the reasons for the situation. From an economic point of view, renovation and the reuse of buildings, which takes into consideration the technical and spatial functions and also the urban and architectural aspects, often appears to provide a better solution.

The aim of the COST Action C16 is to improve techniques and methods used to adapt the envelopes of buildings constructed during the second half of the 20th century in the COST countries. These ‘non-traditional buildings’ were constructed from in situ poured concrete systems, large scale prefabricated systems and/or small concrete/mixed elements although in some countries brick or stone was still used. The demand for housing in the post-war period necessitated the rapid production of large numbers of dwellings. Qualitative aspects were less important. Furthermore dwellings of the types constructed at that time no longer fulfil contemporary or anticipated future demands for housing, with the possible exception only of those built during the last 5 years.

At this stage, it must be noted that two other ongoing Actions in the field of Urban Civil Engineering, also address issues related to buildings: COST Action C12 on “Improving buildings' structural quality by new technologies”; and COST Action C13 on “Glass and interactive building envelopes”.

The Technical Committee on Urban Civil Engineering considers that in addition to the tasks directly connected to the main objective of their Action, participants in the COST Action on “Improving the quality of existing urban building envelopes” should establish and maintain close contacts with the two above mentioned Actions. This will foster co-operation with these Actions and avoid potential overlaps.

About one year after the start of COST Action C16, it was put on a hold for more than 8 months, to permit the ‘renaissance’ of the COST programmes, while in the meantime COST C12 had almost ended and it was considered that the C13 Action had only a slight connection with the targets of COST C16. The CSO therefore agreed with the request of the Management Committee that the end of this Action should also be postponed by 8 months so that it would still last for the planned duration of four years.

SCIENTIFIC PROGRAMME

To date problems relating “Urban Building Envelopes” and their solutions are approached in isolation. The original design planners, architects and engineers work together to realise a building according the current state of knowledge, but this co-operation longer exists during the life-cycle of the building.

For far too long prolongation of the occupation by the use of maintenance was sole aim. If improvement did become an option only a few aspects were considered. At present the current state of knowledge is usually local, being concentrated in some of the housing co-operations, architectural and engineering companies. However much has been done to spread this information in order to initiate discussion about when and how existing buildings with their envelopes can be improved to fit them for the future.

The COST mechanism will foster international concentration on the integrated problems related to non-traditional dwellings. It will create a direction for improvement of urban building envelopes and also illustrate the state of the art in the various countries concerned.. What has already been learned in one country can now easily be shared or can be translated to fit the needs of other countries. His will make the implementation of new practices much easier.

The World Wide Web will be used to bring all the information on the major non-traditional housing systems in Europe together as well as the various techniques for the improvement of urban building envelopes. We are happy to announce that for the first time since the establishment COST, it has become possible not only to publish books but to place the information on the World Wide Web. See www.costc16.org. High schools and universities interested in the subject of the renovation of existing buildings can now have east access to this knowledge.

This study was based on the following scientific programme:

– Description and analysis of the types of system related to the factors influencing urban building envelopes;

– Analysis and comparison of the legislation and technical regulations relating to renovation in European countries;

– Analysis of how urban building envelopes have been changed to date in relation to relevant factors;

– A survey of existing engineering techniques that can be used, modified or developed to reach this goal;

– A synthesis of possible global approaches leading to guidelines on how to reach maximum value for money in relation to the desired quality and working conditions in the urban environment and also how this approach can be reached for other types of buildings.

THE SCHEME OF THE APPROACH OF ACTION C16

The original idea given in the technical annex of the Action was to start with a preliminary approach lasting six months. After that, three working groups would be set up on the themes of: the current envelopes, the needs and the techniques. A period of three years was allocated for this. The last six months of this period would have been used to integrate the result of the working groups and to prepare the final international symposium.

As stated above, one year after the start of the Action C16, together with other Actions, was placed on hold, because of the reorganisation of the COST organisation to create an umbrella organisation. At the beginning of 2004, on the basis of the contract between the European Science Foundation and the European Commission for the Support of COST, this reorganisation started with the establishment of the fully operative COST office in Brussels.

This delay caused to loss of some momentum. A second problem that had to be solved was that the members of C16 came from a variety disciplines and included structural engineers, architects and physicians. Although an interdisciplinary approach is one of the targets of a COST Action, this did give rise to problems in the working group on techniques. For example bearing structures demand a different specialisation from that required for secondary elements, such as facades and roofs. The management committee was wise in its decision to split the Techniques Working Group into a working group on structures and a working group on facades and roofs.

THE METHODOLOGY

The methodology used for the work of the four working groups of the Action C16 “Improving the quality of existing urban building envelopes” differs.

The first book entitled ‘The state of the art’ is divided into two parts. The first part comprises a survey on the housing stock for each country. It contains data related to the building period, main typology and technologies. In the second part the topics covered describe the quality of the housing stock. The ‘state of the art’ depends on the time at which a survey takes place. That is why we consider it an advantage to also publish the two keynote lectures in this first book. These describe approaches to the modification of the multi storey family stock that is currently under investigation.

In the second book, ‘The needs’, the method used to obtain precise information was to develop a table that includes the needs, solutions and priorities for each country. It is evident that these needs and priorities will differ greatly from country to country, as illustrated for example by comparing Sweden to Malta. To determine these aspects, criteria such as land use, architectural aspects and building physics are used, as well as aspects relating to finance and management.

In the third book, ‘Structures’, a framework for possible solutions has been set up. It contains 20 case studies in which changes in bearing structures to fit for future purposes was the goal. Examples include descriptions of how to build extra floors onto existing buildings for both financial reasons and also to make the installation of elevators more profitable.. Another example illustrates the need for greater flexibility, and shows how a part of the bearing structure can be changed to provide this.

In the fourth book, ‘Facades and roofs’, which is based on the results of the working groups' The state of the art' and ‘Needs’, two documents have been developed, ‘Technical Improvement of housing Envelopes’ and ‘Country Criteria in the form of a matrix’. Relations between the most frequently used refurbishing solutions and their impact on sustainability have been worked out in depth. Sustainability is described in a set of performances such as, technical, economic, functional/social and environmental. Case studies illustrate these theories.

Together these books provide much information and can help countries and people to learn from each other. It is my wish that that you will all profit from their content.

Leo G.W. Verhoef (Chairman COST Action C16)

April 2007

This paper describes the rehabilitation project of the Utrillo Building located in La Rochelle, France. The present project has been launched within the national frame of Urban Renovation Plan. It does not consist only of the building rehabilitation, but it aims at a real urban renovation replacing the buildings in a new urban scenario. In the present paper we will focus mainly on the structural aspects of this rehabilitation project.

The ‘Geldershoofd’ building was originally designed as a modular construction. It is fit only for the function for which it was initially intended. Because of the limited strength of the foundation no extra load can be carried. A proposal for strengthening will be shown. Possible measures to stabilize a part of the building after creating bigger openings in the building, such as those used for the 'Hoge poorthuis' are also considered. Finally, the solution for extending floors to the outside of the original facade with the aid of the existing cantilevered concrete beams will be described. The cantilevered concrete beams alone are not strong enough to carry the new floor load.

This paper presents the structural adaptation of the residential buildings “Le Navi” in Florence. As well as tackling the typological, architectural and environmental obsolescence of the multi-storey blocks, the refurbishment programme also achieved compliance with current national seismic regulations. The intervention on the structures involved above all the introduction of tension rods for wind bracing, that improve and reinforce the structure in relation to seismic events.

In the post war construction until the fall of the wall in 1990, about 3 million residential units were built in the former GDR. 27,5 % was constructed using the WBS 70 large panel system. Over one third of the post war building stock is situated in large urban areas like Marzahn (Berlin). Marzahn was built from 1978 on-wards and created almost from scratch until it reached 62.000 housing units shortly after 1990. A redesign has been made for a large building block containing 580 dwellings, situated near the commercial center of Marzahn. The redesign consists of an urban relocation of functions and an adapted traffic plan, but also the complete interior redesign as well as a totally new façade. The interventions are designed as a catalog to be used in transformations of other WBS 70 building blocks.

The paper focuses on some possibilities for enlarging openings in the existing bearing walls in concrete or brick buildings. In the examples shown, enlarging of openings did not always lead to flexibility. Possibly the opening may have still been too small to reach a flexible solution for future tenants or owners. In the case of the example of a pilot project, an entire bearing wall was removed and replaced by a rigid steel frame. The question that arises is in such a case is whether too much support has been taken away. An alternative to this pilot project is described.

The interventions in the ‘Planeten Flats’, which from both architectural and technical points of view was a monotonously repetitive, building, were so spectacular that in 1993 the renovation project was awarded the ‘National Renovation Prize’. In particular the architectural changes which resulted in a clear position of the entrance, the changes in the facade that divide the building into three distinct horizontal layers, and the spacious winter garden with a multi purpose function, give the building a pleasing integrated modern look. In themselves the techniques necessary to reach the architectural goals were not spectacular, but the many technical difficulties that had to be faced are worthy of description. These include different temperature movements in elements that are partially standing and partially suspended and the complicated method used to remove bearing walls and replace them by prefabricated concrete columns to bear the steel beams as supports for the bearing walls above.

This paper presents a number of structural building measures in the residential area Markbacken in Örebro, Sweden. The refurbishment programme was directed towards solving technical problems due to ageing materials and new demands for sustainability, especially for energy saving, and towards making the declining area more attractive on the housing market. The main challenges here, like in most of the post-war housing stock of Sweden, was to improve the accessibility for handicapped, to repair and enlarge balconies, and to add new ones, to adapt flat sizes to the local demands, and to improve the entrances to the buildings, at the same time preserving and carefully developing the architecture.

For the needs of the occupants, only a light weight attic within the frames of the existing structural outline has been designed. Considering that the construction of the attic will also involve terraces, these must not rest on the additionally constructed terraces but on their own cantilever structure resting on the newly designed beams in the transverse direction. The additionally constructed terraces cannot sustain any additional load from the attic.

For the needs of the occupants, enlargement of balkonies of the existing buildings in large panel structural system has been designed. The mass construction of balkonies on large panel systems initiates the need for design of stable structures. Their mass construction in seismically active regions increases the seismic risk, so that errors made in the design and construction might induce heavy consequences during strong earthquakes.

This paper discusses adaptations and alterations in existing buildings, extension and construction of additional floors, and repair of housing development in Malta. These issues become particularly relevant in the case of Malta as an Island State, in view of the limited availability of land for the construction of new residential buildings, and resources. The structural alterations and improvements carried out in existing buildings, and the construction of additional floors are presented with direct reference to typical load bearing masonry structures.

The bigger part of multi-storey apartment buildings in Denmark from the period 1960-80 were fitted with flat roofs covered with asphalt felt. The construction of these roofs and the quality of the asphalt felt used were in general not adequately tested prior to be used, and therefore the majority of them had to be renovated after a shorter period. In stead of just replacing the original roof with a new one, it is now a days rather common to ad an extra storey where that is possible according to local planning. The reason is as a rule based on economical benefits, but very often this extra storey also gives a lift in the architectural appearance of the building. This case has been chosen because the combination of the two seems to be fulfilled.

The case study deals with problems concerning bringing up existing buildings to present days standard of housing design – expressed more specific: the renewing of bathrooms and kitchens in the more traditional built part of the existing stock of multi-storey housing in Denmark. The solution in this case is a complete substitution of a part of the original building. The new part being a reinforced concrete construction made entirely of large prefabricated elements, including fully fit bathroom-units and closed by a curtain-wall. The case should be seen as an example more than the “final solution” – as a radical way to tackle problems in general, not being locked by standards of doing.

For the last two decades, intensive activities on reconstruction, repair as well as enlargement and building of other storeys on existing old residential buildings has been carried out.The reasons for such an extensive reconstruction and building of other storeys onto old residential structures is the increasing need of residential area, revitalization and repair of structures that are 30 to 50 years old as well as improvement of the quality of living of the occupants of those structures.

One of the possible solution for enlarging useable space for existing building is to add stories. Adding new stories involves additional loadings to old structure and to subsoil. Very often calculation and analysis of existing structure and overloading of soil leads to conclusion, that only very lightweight superstructure can be applied. One of such structure can be pre-fabricated steel frame-panel SUNDAY system^TM which includes pre-engineered wall panels, roof trusses, headers and joists in fabrication shop from light-gauge steel stud made on the rollform machine. The combination of only 2 shapes (C and U) in 2 sizes each, with addition of 4 kinds of screws and using different steel gauges for these shapes is able to totally fulfill structural requirements of any structure type specified by the designer for such use. The paper present the case study of application of light steel prefabrication technology for enlargement of existing building by two additional stories.

Necessity for rehabilitation of flat roofs, as well as residential deficit and high prices of flats caused massive annex of attics. In Belgrade in the period after World War II mass building of apartment houses with flat roofs had been extensively used. Flat roofs appeared functionally unsuitable in domestic climatic conditions. Because of improper technical solutions and building practice, flat roofs leaked, causing bad living conditions in flats underneath. As a sloped roof in our environment is traditional form functionally favorable for our climatic conditions, the solution was in annex of attics, representing a characteristic example how climatic conditions create the renewal of existing buildings and urban spaces. The most important benefits to the community are improvement of technical and living conditions in the whole building, especially on the original top floors, and efficient and cost-effective building of new dwellings, as well as improvement of buildings and settlement appearance. Through review of several examples realized in Belgrade, survey of some technique solutions for annex of attics will be given in the paper. Improvement of building appearance will be also discussed.

The renovation of the housing project from 1967 on the Siersteenlaan in Groningen demonstrates that in an integrated approach a wide range of objectives to improve existing buildings can be reached. In this project the goals were the improvement of the urban situation, the architectural appearance, the social control, diversification of dwelling types and a higher functional quality. The solution of the problems was specifically adapted to the existing ‘Rottinghuis’ building system. Large one- and two-floor apartments were created on the ground floor, and the accessibility of the remaining smaller apartments on the upper floors was improved by adding elevators. With diverse additions to the existing buildings different problems were solved. By making as little changes to the structure as possible, the intention to develop more diversification was reached at acceptable cost.

The worst housing problem ever faced by Cyprus appeared after the invasion of 1974 when 38% of its territory was occupied by Turkish military forces. At that time 36,2% of the housing stock was lost and therefore 200.000 refugees had to be settled in the rest of the island. Until 1986 the Government of Cyprus managed to house nearly 50.000 of these people in various refugee estates, according to an intensive housing program. Out of this number, approximately 30% have been settled in multi-story family houses. Today 20-25 years after that ¨housing boom¨, and due to the specific technical, environmental and seismic conditions in Cyprus, as well as the change of the quality of the available building materials, many of these multi-story buildings face a variety of problems. The solutions decided vary from complete demolition to plain painting.

Externally bonded reinforcement offers a strengthening method that enables to solve different frequently occurring problems for the structural frame of the multi story, multi family buildings. The technique can be useful when applying often used interventions such as the removal of supporting walls or supporting columns. It is a technique that can easily be applied to the concrete beams and columns as well as to the concrete floor slabs. This paper explains the basic principle of the technique and discusses two case studies to show the possibilities of the technique.

After 45 years of use without repairs, serious damage of elements of multi-flat apartment buildings is generally observed. In buildings exploited for about 25 years, the effects of corrosion of thin reinforced concrete elements (balconies, loggias, roofs above entrances to buildings and architectural details) are common. Errors in design, realization and maintenance represent a source of the damage.

The paper presents an actual technical state of these elements taking as an example balconies, loggias and the range of their rehabilitation as well as current ways of the surface protection of repaired elements. From the economic point of view it is profitable to connect the rehabilitation of thin reinforced concrete elements, complex repair of buildings and thermo renovation of external walls.

This report is engaged in the current situation of the housing site in eastern Germany. The focal focus is on the measures to reducing the enormous number of empty dwellings. A re-use method is discussed as one option to the present demolition of vacant buildings. Thereby dismantled concrete panels were applied to build new, more effective demand houses.

This paper illustrates the present activities of re-use concrete components from dismantled panel buildings. Considering as examples three little houses are giving an idea how the process of re-use works. The examples are optimized at owner's option. They are showing the architectonical and design engineering possibilities of large panel elements.

This paper gives an overview about typical measures during high-class modernisation of block buildings. The focus is on the construction needs of prefabricated concrete buildings. Three main points are characterized. The first is the creation of new wall openings. The second is engaged in the area of transformation of floor/roof slab elements into roof terraces and the last one describes a possibility to create a barrier-free opening for balconies.

In multi-storey large panel dwelling buildings, external walls were constructed from three layers: façade layer made from reinforced concrete, thermal insulation layer made from polystyrene or mineral wool and structural layer made from reinforced concrete. Connection between these three layers consisted of fasteners and pins made of steel bars. From the safety point of view, the most important structural elements in sandwich panels are steel hangers. The main defects observed in the external panels of existing buildings have been described as well as methods of improving the safety of connections between layers.