Building obsolescence

‘Building obsolescence’ is a term used to describe a building that has become outdated and unfit for purpose. An obsolete building has reached the end of its service life, which will often result in it being neglected or abandoned, resulting in a deterioration in physical condition. Given that buildings represent a significant economic asset for their owners, few buildings are allowed to decay and eventually collapse. Instead obsolete buildings are either demolished or repaired and upgraded for a new function and a new lease of life.

A building may be termed obsolete for one or more of the following reasons:

• Physical obsolescence. Buildings decay over time and without regular maintenance and repair, they will eventually reach a state of physical obsolescence. Given that not all building materials and components decay at the same rate, it is not unusual for the building to exhibit signs of obsolescence in a variety of areas, be it the building fabric or the internal environment. For example, the building fabric may decline at a faster rate than the structural frame, often resulting in the depreciation of the building’s economic value (based on physical appearance and predicted cost of repair and refurbishment). However, the underlying structure of the building may be sound, and it may be possible to upgrade the fabric several times before the structural frame becomes unfit for purpose, at which time the entire building will need to be replaced.
• Functional obsolescence. Technological advances and changes in demand can often render a building obsolete in terms of its function and usability from the perspective of the users. This can be mitigated to a certain extent by designing the building to be adaptable and flexible to different demands and changing technologies, although it is not an easy task to try and predict what we might demand of our buildings 10, 20 or 50 years hence. Photograph 11.1 shows a warehouse that was derelict and subsequently upgraded to luxury waterside apartments. The photograph helps to illustrate the sensitive introduction of new double glazed windows to improve thermal performance of the fabric, with the new steel window frame reflecting the industrial heritage of the building.
• Economic obsolescence. As a building becomes less useful to owners and tenants, there will be a loss in economic value. At some point the amount of investment required to maintain, repair and upgrade the building will become economically unviable based on future predictions of income. This is known as economic obsolescence. For example, with rising energy costs it may become economically unfeasible to sufficiently upgrade the thermal insulation of a building, with the cost of the work far outweighing any future economic savings. At this point it is likely that tenants will move to buildings that have better thermal performance and lower running costs, while owners will seek to dispose of their asset or redevelop the site.
• Sustainable obsolescence. As environmental legislation becomes ever more stringent and awareness of sustainable issues becomes more widespread, it has started to alter how we perceive our building stock. What was once a perfectly acceptable building may start to be perceived by owners and tenants as no longer sustainable, because it no longer satisfies new performance criteria (e.g. carbon reduction targets). When it is not physically possible, or economically viable, to upgrade the building to meet new environmentally sustainable guidelines and legislation, then the building will be deemed to have reached a state of sustainable obsolescence. This may result in tenants moving to buildings that better suit their organisation’s environmentally sustainable values, or alternatively it may lead to a programme of upgrading and retrofitting.

Research and recording

A full understanding of the building’s social and technical history is essential prior to carrying out any interventions. When dealing with any aspect of an existing building, there will undoubtedly be some challenges in accessing information about the building’s construction and use; however, information can be collected from a wide variety of sources, helping to provide some contextual data. Measured survey drawings, as‐built drawings, written descriptions, specifications and photographs will be useful. So too will local government records for planning and building regulation control and other documentary sources such as insurance records. In attempting to gather information about buildings, it is essential that the search is methodical and critical. All sources should be accurately recorded and an accurate record built up through constant cross‐checking of information. A good starting point is with the original date of the building, if this can be established quickly; for example, from a date stone in the fabric or through local records. Since the late 19th century, architects and builders have been required to submit copies of their plans and proposed construction details to the local authority building control department for approval. This body of information can provide an important source of material, the date of design, construction details, survey drawings, etc. Unlike planning records, permission to access the drawings will be required for security purposes. Information sources may comprise some or all of the following:

• Maps and plans
• Title deeds
• Newspapers and journals
• Town planning records
• Building control records
• Records held by local builders and consultants
• Local knowledge
• Specialist publications and books

Whether this exercise is conducted before, after or concurrently with an assessment of the building’s condition will depend upon circumstances relating to a particular building. The important point is that it must be done before any objectives, design work or building work is carried out.

Analysis of condition

On site investigation and analysis should not be carried out until at least some of the information required has been found; this knowledge helps to focus the attention of the site survey and also aids the understanding of health and safety considerations. Designers need to be rigorous and systematic in their observation and recording of what they find. Photographs, video and thermal imaging can supplement this exercise. Photograph 11.2 provides an example of modest ‘opening up’ of an existing house to try and establish what was behind an existing wall.

The most common methods of data collection are:

• Measured survey. A detailed measured survey of a building and its immediate environs will enable accurate plans, elevations and sections to be produced. Undertaking this exercise also allows those conducting the survey to experience the building at close quarters and hence get a good feel for its character. The survey drawings may differ from historical data because of inaccuracies in original drawings, variations from the drawings during construction and/or because of unrecorded changes made to the building post‐construction.
• Condition survey. Analysis of a building’s physical condition is known as a condition survey and the resultant report is known as a condition report. Condition reports serve two purposes. First, they should provide an accurate and comprehensive description of the condition of the building fabric, structure and services. Second, they should act as an information source on which decisions can be made. Thus the report must be well structured, clearly written, and contain concise conclusions and recommendations.

• Post‐occupancy evaluation (POE). This term covers the monitoring of buildings to see how they are used over time, i.e. how they perform. This is an important consideration for commercial and public buildings that have to be managed to support business objectives. Evaluation and monitoring of an existing building are usually done for one or more of the following reasons, namely, to evaluate and monitor the:
  • Performance of the building against specified criteria (e.g. energy consumption and thermal comfort of the occupants)
  • Functionality of the building against its current (or proposed) use
  • Building users’ behaviour, with a view to improving working conditions, physical comfort and wellbeing
  • Maintenance and operating costs (heating, lighting, cleaning, security, etc.)

Concomitant with other data collection exercises, the purpose should be clearly defined and necessary approvals sought and granted before data collection begins. Similarly, methodologies for evaluation should be kept simple, have measurable outcomes, be properly resourced and have a realistic timeframe. Whatever method is used, the data recorded should be used to aid decision‐making. The outcome is likely to be one of the following:

• Do nothing
• Conserve (and or preserve) the building
• Retrofit to upgrade the functionality of the building
• Remodel the building to suit a new use
• Demolish and recycle

The ‘do nothing’ option may be taken due to financial and procatical limitations; however, putting off a decision to, for example, repair a part of a building usually results in more expensive repairs at a later date. The options of conserving, retrofitting, remodelling and demolition are discussed after we understand the underlying reasons.

Agents of decay

Over time, buildings are subjected to attack from a number of different sources. Sometimes these agents of decay act independently, although it is more common that they act in conjunction with one another. The rate of decay can be reduced through sensitive detailing and materials selection, competent construction and proactive management of the building during its life. Agents of decay may be classified as being biological, chemical, electromagnetic, human, mechanical and thermal.

Construction defects

Despite everyone’s best intentions, it is possible that some faults and defects will be found in the completed building. Some of these will be evident at the completion of the construction contract, but some may not reveal themselves until sometime in the future and are known as ‘latent defects’. Many years may pass before the defect becomes apparent, especially where it is hidden within the building fabric. Performance monitoring during and post‐construction can help to identify some of the defects before they pose a threat to the building fabric. Defects can usually be traced back to one or more of the following:

• An inability to apply technical knowledge
• Inappropriate detailing and specification
• Non‐compliance with regulations and codes
• Incomplete information
• Late information
• Late design changes
• Poor work
• Inadequate site supervision
• Inappropriate alterations rendering an otherwise good detail ineffective
• Insufficient maintenance

We can, for simplicity, divide defects into two categories: those concerning products and those associated with the process of design and construction.

Maintenance and repair

Deterioration cannot be prevented, but it can be retarded through a combination of good detailing, good building and regular inspections and maintenance. Recurrent maintenance costs are a financial drain on building owners, and the act of maintenance may also be disruptive to the building users. This sometimes leads to maintenance work being postponed, often with consequences for the building. Efforts to reduce the frequency and extent of maintenance through sensitive selection of good‐quality building products and sensitive detailing are likely to result in reduced life cycle costs for the building owner. However, there is still a requirement for regular inspection, cleaning and routine maintenance, which must be factored into the whole life costs of a building at the design stage.

Maintenance and repair should benefit the building, not hinder its aesthetic appeal of technical performance. The repair of buildings is often undertaken in an ad hoc manner, in stark contrast to the time and effort spent on the original building project. Inconsistency will usually devalue a property and may lead to unforeseen problems with the performance of the building fabric. It is essential that those carrying out maintenance and repairs understand the way in which the building was designed and assembled so that maintenance does not compromise performance. This means that those responsible for maintenance must have access to the as‐built drawings and associated documentation.

Listing

Listing aims to protect a building from demolition or insensitive alterations and repairs, helping to retain the architectural character and cultural importance of certain buildings. Buildings may be listed because of their age, architectural merit, rarity and their method of construction. Buildings may also be listed because of their cultural significance, for example, being the birthplace of an important person.

Buildings, ranging from industrial buildings to pubs and post‐war schools, may be surveyed and considered for listing once they are 30 years old. There is an additional rule which allows exceptional buildings between 10 and 30 years old to be considered for listing if they are threatened with demolition or alteration. The listing grades for England and Wales are explained further, with Scotland and Northern Ireland using the grades A, B and C:

• Grade I – exceptional. Covers buildings of national importance and some of international importance.
• Grade II * – unusual. Of significant regional importance and some of national importance.
• Grade II – still valuable. Of significant local importance, warranting effort to preserve them.

Listings and further information can be obtained from the local authority responsible for a particular geographical area. Once buildings are listed, alterations or demolition cannot be undertaken without first applying for and receiving listed building consent from the local authority planning department. Listing does not mean that buildings cannot be altered, but any proposed alterations will receive rigorous scrutiny to make sure they are sympathetic to the existing character of the building. Listings provide greater protection to buildings than a local authority declared conservation area does. In the majority of cases, listing will improve the financial value of a property.

Work to existing (historic) buildings

When working on an existing building, the design solutions will be influenced by the building’s existing character and context, each providing limitations and opportunities. For a listed building the main objective will be to conserve the building through stabilisation of the fabric and structure, and sensitive repair work will help to extend the serviceable life of the building. The manner in which this is achieved will depend upon the importance of the building and its intended use. Photograph 11.3 shows a window in a listed building, being repaired using traditional materials and techniques to retain the existing character of the building.

New uses for redundant buildings require a complete understanding of the building’s construction, structural system, material content and services provision, as well as an appreciation of the cultural and historical context in which the building is set. A checklist would need to cover the following issues:

• Access limitations
• Accoustic and thermal properties of the fabric (and potential for upgrading)
• Assessment of embodied energy
• Condition of the fabric
• Condition of the services
• Contaminants (e.g. presence of asbestos, lead paint, etc.)
• Economic factors and life cycle analysis
• Fire protection and escape (to current legislation)
• Health and safety factors
• Historical context of the building and its immediate surroundings
• Legislation, including site specific constraints
• Potential for reuse and recovery of materials (partial demolition)
• Reuse or demolish
• Scope for new use (and future reuse)
• Social context
• Stability of the structure and foundations (capacity for increased loading)

These factors need to be considered before the brief is finalised or design work commences. They should form an essential part of the critical condition survey and feasibility study.

Architectural character

Alterations and extensions, no matter how minor, will affect the building’s character. The application of new construction techniques to regional traditions of building, using locally available materials and labour, may be one (sustainable) approach to enhancing the character of a building. Responding to the existing building fabric and the spirit of the place is a good starting point for many designers and is often the preferred approach of town planning officers and the immediate neighbours. However, it is possible to introduce modern materials and methods to existing buildings and hence enhance their architectural character. Successful remodelling of buildings is usually achieved by employing one of two design strategies:

• Match existing. Use of materials and building techniques to match those used previously, a continuation of tradition through colour, texture, application, scale and design philosophy. Specialist publications and design guides are essential reference tools.
• Contrast existing. Use of materials and building techniques to contrast with those used previously. A break with tradition, through the use of new materials, contrasting textures, new techniques, different scale and new design philosophy.

Both are sympathetic approaches which are usually successful, the philosophy adopted depending upon the wishes of the client, town planners, designers, constructors, context and the resources available. Done well, the building will outlive its custodians and will probably be remodelled again in the future. Done badly, the value of the structure can be affected negatively, and future alterations and maintenance are likely to be more expensive than they should have been.

Upgrading thermal performance

Few of the existing 22 million homes in the UK operate close to the current energy standards expected and legislated for. This means that a large proportion of the domestic building stock is in need of a thermal upgrade. This is also the case in the non‐domestic sector, where the majority of existing buildings fail to meet current standards for thermal insulation. Upgrading (retrofitting) the thermal insulation of buildings requires a thorough understanding of the existing building fabric. Failure to appreciate that many interventions will change how the building ‘breathes’ and reacts to changes in temperature and use may lead to a deterioration of internal air quality, surface condensation and interstitial condensation, leading to deterioration of the fabric. Interventions must be considered in relation to the whole building and the detailing adjusted to suit the physical personality of the building. Sensitivity is required to ensure that the efforts to reduce energy consumption do not make the building’s environmental credentials worse. We also need to take a long‐term view, not a short‐term ‘quick fix’ and consider the environmental impact of potential upgrades. Some of these issues have already been explored in Barry’s Introduction to Construction of Buildings, Chapter 13. Typical interventions that can be carried out without major disruption to the building users include:

• Improving the thermal insulation of walls and roofs
• Replacing single glazed windows with double or triple glazed units
• Installing insulated, air tight, external door sets
• Improving the air tightness of buildings
• Installing heat recovery ventilation systems
• Installing solar collectors (solar thermal) and PV cells (electricity) on roofs
• Replacing boilers with high efficient condensing gas boilers
• Replacing lighting with low‐energy fittings

It may also be possible to reduce the thermal bridging in some buildings, although this can be technically challenging, highly disruptive and expensive, unless it is done as part of an extensive retrofitting exercise with users relocated during the work. The challenge for building owners is that the payback period on investing in retrofitting buildings is lengthy. Thus it is necessary to also look at the positive effect on user comfort and wellbeing, which is not easy to allocate a cost.

Upgrading accessibility, usability and comfort

Alterations to facilitate disabled access are a major challenge for many building owners. Changes in level and various widths of access may contribute to the character of a building, but these features can, and often do, create barriers to access. Providing equal access for all often requires structural alterations and careful detailing, which must be done sensitively if the character of the building is not to be unduly affected. Equally, the implementation of (non‐intrusive) fire detection and security equipment requires sensitivity to the building’s character.

Upgrading the usability of interior space and the overall comfort of the building users is another concern. Buildings must be seen in the context of the society and the people who interact with them; thus user feedback is crucial in formulating the design brief. Asking users how much control they wish to have over their internal environment can be instrumental in formulating design solutions. For example, the ability of users to have local control over light levels, heating and airflow may influence their perception and comfort of their internal space. These are important issues for the usability and comfort of building users as well as for the operation of the building.

Indoor air quality and condensation

With the drive to save energy has come the need to thermally insulate buildings to a high standard and to restrict the loss of heat caused by air leakage. The result is highly insulated, airtight buildings. Unfortunately, in meeting one set of requirements, in this case improving thermal performance, it is also possible to unwittingly create problems, such as interstitial condensation in the fabric. This should have been considered and designed out at the design stage for new buildings, but the issues are not so straightforward when upgrading and retrofitting existing buildings which may have been perfectly balanced for years.

Problems tend to relate to insufficient airflow within the building, which may cause problems with the health of the occupants and also result in condensation on, and within, the building fabric. A common problem is related to the replacement of windows and doors in existing buildings to improve the thermal performance of the building. The poorly fitting windows and doors would have been allowing air infiltration, which reduces the thermal performance of the building through unwanted airflow, but also allows excessive moisture to leave the building through air changes. In replacing the windows and doors with new airtight units, the flow of air into and out of the building is significantly reduced. Similarly, the relatively innocent act of blocking up or removing a chimney can have a dramatic effect on airflow. The result is that the internal climate may become stale through insufficient airflow and excessive moisture in the air is unable to escape the building, resulting in condensation on cold surfaces and within the fabric.

Façade retention

Not all existing buildings have sufficient structural properties for the proposed new use, and a considerable amount of structural work may need to be undertaken to ensure that the structure is made good. In many cases, the foundations may need to be strengthened and underpinned and the structure reinforced. In some cases, the structural work is so extensive that the only part of the original structure retained is the façade. Façade retention involves retaining only the external building envelope or specific aspects of the external fabric. This may be all of the existing walls, or in some cases, it may be as little as one elevation of the building only. The internal structure and majority of the building fabric is demolished to make way for a new structure behind the retained (historic) façade. Removing the main structural and lateral support (walls and floors) from the façade will render it unstable. A temporary support system must be put in place to hold the façade firmly in place while the existing structure is removed and the new structure installed. The temporary support system must be able to provide the necessary lateral stability and resist wind loads. The support systems may be located:

• Outside the curtilage of the existing building – external support
• Inside the curtilage of the existing building (behind the façade) – internal support
• Both external and internal to the existing building – part internal and part external

Figures 11.1 and 11.2 provide examples of external, internal and part internal‐part external façade retention systems. Each support system is designed specifically to suit the façade that is being supported and the process used to construct the new building. As well as supporting the walls of the façade, it may also be necessary to support adjacent buildings that previously relied on the support from the original building.

Various methods of retaining the façade and constructing the new works are used (see Photograph 11.5). This is a specialist field, so a summary of the principal issues that must be addressed is provided as follows:

• Temporary support to the façade – throughout the works
• Must retain the façade, prevent unwanted movement, allow for differential movement and resist wind loads
• Permanently tying back the façade to the new structure
• Façade ties must restrain the façade and prevent outward movement away from the new structure
• The ties must not transmit any vertical loads from the existing structure to the façade
• Allowance for differential settlement between the new structure and the retained façade
• Ties to the new structure must be capable of accommodating such movement
• Ensure the new foundations do not impair the stability of the retained façade
• Underpinning may be necessary to ensure that settlement is controlled

Temporary support

Temporary support to the façade can be provided by steel tubular scaffolds constructed to hold the fabric firmly in place until the new structural frame is built (Figure 11.3). When the temporary support is in position, the demolition operations to the main structure can start. As the new structural frame is constructed, the façade can be tied to it. Where possible, the scaffolding façade ties are taken through the window openings to avoid the need for breaking through the façade or drilling into the masonry to fix resin or mechanical anchors. Drilling and other potentially damaging operations should be avoided where feasible, especially if the façade is of architectural merit and/or town planning restrictions apply.

Where the wall is clamped with a through tie, timber packing either side of the tie is used to provide a good contact with the surface. Surfaces of a façade are often irregular and the thickness of the remaining structure may vary. Timber packing, felt and other slightly resilient and compressible materials should be used to secure the façade surface and protect it by preventing direct contact with metal supports.

The lateral forces applied by the wind may mean that the scaffolding needs to be trussed out, with kentledge applied (load to hold the support down), or flying shores may be needed to transfer the loads (Figure 11.4). The design of the shoring system is dependent upon the position and number of walls and floors retained and the position of the new structure and its floors. The installation of shoring should be coordinated with the demolition and installation of the new frame. During the demolition operations, it is essential that the integrity of the remaining structure be maintained. Only when the final structure is erected and the façade fully tied to it, can the shoring be removed completely.

Flying shores may be used to brace the structure against wind loads. These can only be used where there is an adequate return (e.g. the opposite face of the building). Depending on the direction of the force, the loads are transferred across the truss, down the opposing scaffold and to the ground. Foundations to the scaffold are used to ensure that the loads are adequately transferred. The scaffolding and the shores may be designed to resist both compression and tension, so the foundations must be capable of resisting uplift and compression, acting as kentledge and a thrust block.

Deflection must be limited to preserve the integrity of the retained structure. Flying trusses are constructed with a camber to reduce the impact of sagging. Intermediate scaffold towers can be used to reduce sagging, although the supports may impede the work. Where there is sufficient room outside the structure, raking shores will be used to provide the main structural support to the façade. The construction of reinforced concrete lift shafts and service towers can be used to transfer the loads to permanent structures at an early phase in the construction process.

Hybrid and proprietary façade support systems

A variety of structural formwork or falsework systems can be used, in conjunction with steel tubular scaffolding, as a hybrid system. Alternatively the tubular, manufactured or patented systems can be used on their own to provide the required support (Photographs 11.6 and 11.7). The system illustrated in Figure 11.5 provides a schematic of the RMD support system; this can be used externally, as shown in the diagram, internally or as a part internal‐part external frame. The components fix together to provide a strong rigid frame. Often the areas between each lift of the supporting structure are used to house temporary site accommodation. In larger structures, multiple bays are used, which are fully braced to provide the required support (Photograph 11.6).

Fabricated support systems and use of new structure

It is also possible to limit the amount of temporary scaffolding and support systems by making use of the new structural frame (Figures 11.6 and 11.7). Although logistically complicated, in some buildings, it is possible to bore through ground floors to construct new foundations, puncture holes through upper floors and walls, and erect part of the new structural frame before removing the main supports of the existing structure. In order for such operations to be undertaken, a thorough structural survey is required, and careful planning of the demolition sequence is necessary. Figures 11.6 and 11.7 show the façade tied to part of the new structure.

All façade retention schemes are expensive, so rather than using a scaffolding system, some retention schemes make use of specifically designed and fabricated rolled steel beams and columns to provide support to the external face of the façade. Because the structure surrounding the exterior of the building is only temporary, each of the beams and columns can be recycled and reused, and therefore the system may not be as expensive as it first appears.

Planning

It is essential that a full structural and condition survey is undertaken, so that a detailed method statement can be prepared and the appropriate demolition techniques determined. The survey may be supplemented with details of as‐built drawings and structural calculations (if available). Special measures are required for the controlled removal of hazardous materials, such as asbestos and the segregation of materials to ensure maximum potential for recycling/reuse. Demolition operations must be carefully planned and each stage monitored so that the structure can be taken down without any risk to those working on the site and those in the local vicinity of the building.

Information that should be collected on a demolition survey includes:

• Existing services – live and unused services
• Natural and man‐made water courses
• Presence of asbestos and other hazardous materials
• Distribution of loads
• Building structure, form and condition
• Evidence of movement and weaknesses in the structure
• Identification of hazards
• Distribution and position of reinforcement – especially post‐tensioned beams
• Allowable loading of each floor (for demolition plant)
• Stability of the structure
• Survey of adjacent and adjoining structures
• Loads transferred through adjoining structures
• Loads transferred from adjoining structures
• Access to structure – allowable bearing strength of access routes

Prior to demolition, the following tasks should be undertaken:

• Conduct a site survey.
• Contact neighbours and relevant authorities (local authority, police) to discuss the options.
• Identify any structural hazards and reduce or eliminate associated risks.
• Select an appropriate demolition or disassembly technique.
• Identify demolition phases and operations.
• Identify communication and supervision procedures.
• Organise logistics and identify safe working areas and exclusion zones.
• Erect hoardings, screen covers, nets and covered walkways to provide protection to the public.
• Identify need for temporary structures and controlled operations to avoid unplanned structural collapse.
• Select material handling method.
• Identify procedure for decommission services and plant.
• Identify recycling/reuse of materials and components and disposal methods and processes.
• Ensure health and safety processes are not compromised during the process.

After demolition, the following tasks should be undertaken:

• Conduct a survey to determine the extent of any damage to neighbouring properties, and agree on measures to repair any damage.
• Clean up all dust and debris from surrounding areas on a regular basis.

It is often necessary to provide restraint to walls that are to remain after buildings have been demolished. Photograph 11.8 shows flying shores bridging the gap created when a terraced house was demolished. When party walls need support as existing buildings are removed, lateral restraint can be provided in the form of flying trusses made out of tubular scaffolding (Photograph 11.9). Raking shores are often used to provide lateral restraint to walls adjacent to demolition works.

Demolition activities are usually conducted in stages. First is the ‘soft strip’ (or ‘stripping out’) process, in which the most valuable materials, components and equipment are removed. This can be a lengthy and labour‐intensive process to allow the careful and safe extraction of items so that they are not unnecessarily damaged, thus maximising their reuse potential and hence their value. The type of materials, components and equipment extracted at this stage will be heavily influenced by their commercial value. The soft strip is followed by the main demolition stage, which usually starts at the top (roof covering) and finishes with the main structural elements and foundations.

Demolition methods

A wide range of approaches may be taken to the demolition of a building, ranging from controlled explosions to reduce an entire structure (i.e. a high‐rise block of flats) to a pile of debris within a few seconds, through to a sensitive and time‐consuming piece‐by‐piece process of disassembly by hand. The methods chosen are determined through evaluating the risks and value inherent with each method in relation to the specific context of the building and its immediate environment. Timber and steel‐framed buildings tend to lend themselves to dismantling. Many masonry buildings lend themselves to demolition by mechanical pushing by machine using a pusher arm and/or demolition using grapples and shears. Some of the more common methods for demolishing concrete elements include:

• Ball and crane. One of the oldest and most common methods for demolishing masonry and concrete buildings is a crane and a wrecking ball. The heavy ball is either dropped or swung into the structure, causing significant damage and gradual collapse of the building. Some additional work may be needed to cut reinforcing in concrete elements to facilitate demolition. Limitations with this method relate to the size of the building and the capacity of the crane and wrecking ball as well as safe working room. Constraints on working may relate to surrounding structures and overhead power lines. This method creates a significant amount of noise, dust and vibration, and there is always the risk of flying debris.
• Bursting by chemical and mechanical pressure. In situations where noise, vibration and dust need to be kept to a minimum it will be necessary to use bursting methods. Pressure is induced in the concrete by chemical reaction (insertion of expansive slurry) or mechanical means (application of hydraulic pressure). Holes are drilled into the concrete and force applied to the hole; the lateral forces build up over time, resulting in the concrete to split (crack). The smaller units are then removed by crane or by hand.
• Cutting by thermal and water lance, drills and saws. Thermal and water lances may be used to cut through steel and concrete. Diamond tipped saws and drills may also be utilised.
• Explosives. Often used for removing large quantities of concrete. Explosives are inserted into a series of boreholes and remotely detonated. The explosive charges are timed in a sequence to ensure the building collapses (implodes) in the desired manner with the minimum of damage to surrounding buildings from debris. Surrounding buildings may need to be protected from damage by vibration and air blast pressure. Roads will need to be closed around the site and inhabitants removed from nearby buildings prior to the controlled explosion(s). After the explosion there will be a need to clean up dust from surrounding areas and make good any damage.
• Pneumatic and hydraulic breakers. Machine mounted hammers are used to break up concrete floor decks, bridges and foundations. The hammer size will be determined by the strength of the concrete and the amount of steel reinforcement contained within the structure. Telescopic arms (booms) and remote control allows access to otherwise difficult to reach areas. Disadvantages include noise, vibration and dust generation.

Recycling demolition waste

A high proportion of demolition waste can be recycled and/or reused. Material recovery from the demolition makes environmental and economic sense, and the amount of material being recovered and reused is steadily increasing due to environmental concerns and the cost of taking materials to licensed waste sites. Examples of materials that can be recovered and recycled include:

• Aggregates (sub‐bases to roads and foundations)
• Concrete (including products extracted in their original form (e.g. blocks and slabs)
• Glass
• Gypsum
• Masonry (bricks and blocks)
• Metals (aluminium, copper, lead, steel, tin, zinc)
• Mineral waste (tarmacadam and road planings)
• Paper‐based products
• Paving slabs and flags
• Plastics
• Soil (top soil and excavation spoil)
• Stone and granite sets
• Timber

The design and construction of buildings should consider the whole life cycle of the building, which includes demolition (disassembly) and materials recovery. This requires clear decisions to be taken at the design and detailing phases about the materials to be used, the manner in which they are assembled and how they are fixed to neighbouring components. Method statements should clearly describe the assembly and disassembly strategy to aid future materials recovery and reuse without unnecessary damage to components.

Salvaged materials

Materials recovery from redundant buildings has occurred throughout history, with materials being reclaimed and reused in a new structure. Stone and timber were reused in vernacular architecture, while more recently steel and concrete have been recovered and reused.

Architectural salvage, taking materials such as roof slates, bricks and internal fittings from redundant buildings for use on new projects, such as repair and conservation work, is a well‐established business. The cost of the material might be higher than that for an equivalent new product, because of the cost of recovery, cleaning/reconditioning, transport and storage associated with the salvage operations. Reuse of materials and components in situ may be possible for some projects, which may help to reduce the cost and associated transportation. There is also a price premium for buying a scarce resource that will have a weathered quality that is difficult, if not impossible, to replicate with new products. However, the use of weathered materials may be instrumental in obtaining planning permission for some projects located in or adjacent to conservation areas, and so these materials can provide considerable value to building projects.

Quality of reclaimed materials is difficult to assess without visiting the salvage yard and making a thorough visual inspection of the materials for sale, and even then there is likely to be some waste of material on the site. For example, the reuse of roof slates will be dependent upon the integrity of the nail hole, and many slates will need additional work before they are suitable for reuse. In some cases, the slates will be unsuitable for reuse because of their poor quality. For work on refurbishment and conservation projects, the use of reclaimed materials is a desirable option. However, the increased cost premium for using weathered materials with a reduced service life may not be a realistic option for some projects. Another option is to use building products that have been made entirely from, or mostly from, recycled materials.

New products from recycled materials

A relatively recent development is for manufacturers to use materials recovered from redundant buildings, as well as household and industrial waste. Over recent years, there has been a steady increase in the number of manufacturers offering new materials and building products that are manufactured partly or wholly from recycled materials. These are known as recycled content building products (RCBPs), innovative products that offer greater choice to designers and builders keen to explore a more environmentally friendly approach to construction. Many of these products are also capable of being recycled at a future date, thus further helping to reduce waste. A few examples are listed here:

• Glass. Recycled and used in the manufacture of some mineral thermal insulation products and as expanded glass granules in fibre‐free thermal insulation
• Rubber car tyres. Used in the manufacture of artificial stone and masonry products (see Photograph 1.2)
• Salvaged paper. Used in the manufacture of plasterboards and thermal insulation
• Plastics (including PET plastic drinks bottles). Used for cable channels and sorted plastics recycled and used for foil materials and boards

The issue of material choice and specification was discussed in Chapter 1, where the perception of risk associated with new products and techniques was discussed. The perception of risk associated with the use of new products is likely to be higher than that for the established and familiar products, which have a track record. Many of the recycled content products have different properties to the existing products they aim to replace. For example, inspection chamber covers and road kerbs made of recycled content plastics have different structural and thermal properties to the more familiar iron and concrete products, and this will need to be considered in the design and specification stage. The majority of products also being manufactured from recycled materials are produced by relatively new manufacturers, offering products that may have little in the way of a track record in use. Thus the perception of risk is likely to be high until the products have been used (by others) and are known to perform as expected. This should not, however, stop designers, specifiers and builders from doing their own research and making informed decisions.