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Design and Detailing for Deconstruction home | introduction | context | resource efficiency | design approach | principles | details |
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Top of chapter 5 |
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Insulation and airtightness features of buildings often require upgrading, but the reasons and timeframes for this are quite different from either the structural basis of a building, or the external or internal skins, and so we suggest that insulation is considered separately, and treated as a separate ‘layer’ in the construction wherever possible. It is important to ensure that insulation levels can be upgraded without damage or disruption to the structural forms of the building, and furthermore that the skins of the envelope can be repaired or replaced without disruption to the insulation and airtightness layer. Sprayed insulation, such as cellulose fibre or urea formaldehyde, is difficult to salvage during deconstruction, whereas blown insulation can be extracted although this involves the use of a suction machine and certain details have been fulfilled such as the avoidance of bonding resin. Both rigid and flexible slab or batt insulations can in theory be reused, but rigid slabs tend to be easily damaged while flexible batts offer greater potential for simple reuse, as long as it has not collected too much dust and detritus. Natural materials such as cellulose insulation and sheepswool offer the greatest potential for waste reduction since they are ultimately biodegradable and so represent a zero waste option in the long run. Appropriate storage of recovered insulation is vital to prevent degradation. The external skin of any building has a number of functions to fulfil, most of which involve protection from the elements, although aesthetics plays an important part. Strategically, it is worth assessing the differential weathering likely to be experienced across the outer surfaces of the building. For example, corners are often particularly vulnerable, as well as the lowest sections of cladding, where splashback can lead to discoloration and decay in organic cladding materials. If possible, these areas should be made separately removable for more frequent maintenance, repair or replacement. The weathering skin should be removable without damage and disruption to the insulation layer and the structure, though this is not always possible, depending on the overall construction type chosen. This ‘replaceability’ also has advantages when wishing to upgrade external appearances for aesthetic reasons only. It is tempting to specify bonded elements for a building skin, which combine insulation with cladding, for speed of construction, but this usually defeats attempts at deconstruction, as the elements cannot be recycled or re-used easily [22] [23] and wastage rates are increased when failure of one component leads to the unnecessary wastage of the other. The size of cladding elements should be kept small enough for easy manual replacement as well as deconstruction. Wear and tear on large elements can create excessive wastage, as the whole element has to be replaced rather than patched. Internal building finishes may be considered in a similar fashion. Differential wear and tear can be anticipated with good design, and careful detailing will enable worn or unwanted surfaces to be removed without disruption elsewhere. The rapidly changing aesthetics of finishes means that assemblies with removable finishes are particularily effective because they can be easily updated during a refit, without having to remove the entire assembly. Services must be carefully pre-planned to optimise opportunities for deconstruction,as they will inevitably be replaced several times during the lifetime of an average building. Typical services installations include:
Bearing in mind the ‘Layering” diagram shown earlier, it follows that services will last longer than some internal finishes, but should be separately accessible in a way that does not compromise the finishes, the insulated and airtight envelope or the structural integrity of the building. Strategic routing of the services should enable easy access and alteration and have minimum of interpenetration between other layers. Sometimes the simplest technique is to surface mount the services, though this should not compromise the potential to upgrade and maintain the internal finishes. A more common strategy is to provide a service void in certain areas, with simple access at critical points. In this way services are generally concealed and decoration and cleaning are easier on a day to day basis. The routing of services should be pre-planned in relation to all sectional and plan detailing. It is important to obtain accurate service route plans at the contract design stage and as built drawings from service engineers and contractors whenever possible as part of the contractors requirements. The use of nominated contractors can help in this regard on larger projects. All servicing fixings should be designed to be fully reversible, given the relatively short life span of servicing products and equipment. The use of suspended service trays for cabling and appropriately sized service ducts can ensure the separation of pipework and cabling to enable easy deconstruction. The use of passive environmental strategies such as thermal mass for cooling and passive solar gain for heating, as well as “breathing” walls for ventilation can significantly reduce the amount of mechanical servicing needed in a building, which in turn can ease deconstruction. 5.10 Key construction materials : re-use potential Steel, masonry, concrete and timber comprise the vast bulk of construction materials and all offer possibilities for reuse where fixings have been designed to facilitate this. Timber tends to be susceptible to poor practice and is not re-used as often as steel and masonry. Glass and plastics tend to have limited reuse potential, and are generally more suited to recycling. |
Flexible insulation bat
Bonded external
Un-treated timber
The weathering skin
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Steel is extensively |
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Re-using bricks |
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Concrete paviors can |
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Example of re-used |
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There is a perceived risk among designers in the specification of re-used or recycled components and materials. In fact, the re-use of construction elements is not innovative; it has being going on for centuries, relying on the experience of the builder, designer and inspector rather than any set standards. Providing clear audit trails combined with expertise in inspection can help to clarify the provenance of materials and components as well as meet required standards. This process can often satisfy indemnity demands, as “due diligence” has been demonstrated. Additional visual inspection, or testing for certain materials or components known to be prone to decay, can be added to this to further minimise risk. Where there is no audit trail available for a material or component, it is important to engage the services of an expert inspector (as provided by Bioregional Reclaimed, for example). There is an urgent need for more training in this area. In terms of site practice, design and detailing for deconstruction aims to minimise the risk involved in dismantling buildings. Demolition contractors prefer to dismantle buildings mechanically using automated equipment that operates remotely as this minimises the risk to the operative. Dry-joint systems rather than infill jointing and applied finishes can ease risk, providing the operative is fully briefed on the process involved. Pre-planning is essential and involves the designer considering exactly how their design can be safely taken apart and ensuring that this is written into the contract prior to construction. The use of building logbooks which detail what has taken place in a building in terms of maintenance, replacement and alterations, is potentially an invaluable tool for deconstruction purposes. It has also been suggested by BRE that Material Recovery Notes (MRNs) (Hurley, 2003) should also be developed which can communicate information on key demolition/deconstruction products, and which can follow the product or assembly throughout its lifecycle. MRNs and logbooks can also minimise health risks by demonstrating the exact nature of any given assembly or product at any given time. If a “clean” approach to design for deconstruction is adopted, which favours mechanical fixing and finishes over the use of chemical joints and applied finishes, this will also help to reduce any potential cross-contamination of products and materials, which is one of the major perceived risks in reclamation. There is far more potential opportunity to detail for deconstruction that will take place during the maintenance and alteration of existing stock, given that the rate of replacement of the building stock through new build relatively small [25]. This does, however, place particular demands on the designer. When designing for existing buildings, the first action should be to carry out a detailed audit and evaluation of the buildings’ existing potential for deconstruction and re-use. Older buildings are often more “re-usable” than we think, with a significant amount of high-quality and durable components that can be identified in a reclamation audit for either reuse, reclamation or recycling. It is important to consider the amount of embodied energy tied up in each disposal option, and decide which option preserves the greatest amount of resource and embodied energy for the least energy cost. The historic value of any component should also be considered when evaluating the options. Construction waste can be further minimised by good site practice to ensure that the demolition process carefully segregates reclaimable materials and products. Good conservation practice which demands “reversibility” of detailing can help facilitate deconstruction of design interventions in older buildings. “Reversible” design can also help to preserve the inherent flexibility and adaptability that many older buildings exhibit, prior to the second world war. 19th century buildings often used relatively soft mortars for masonry as well as details facilitating the removal of key elements. Buildings constructed in the late 20th century and beyond, however, tend to use stronger mortars and other fixing and finishing techniques that make deconstruction more difficult. When detailing for alterations to existing buildings, the designer should strive to preserve any inherent deconstructability by ensuring that additions are “layered” on for easy removal. Fixing directly into masonry should be avoided, and the mortar joint used instead, to preserve the existing elements. Servicing should also be carefully designed to be “reversible”. There is not excellent guidance on this (Warm, P. and Oxley, R. 2002). There are certain additional risks involved when altering existing buildings in relation to design for deconstruction, that must be considered. While it may well be possible to design in a careful audit trail for products and assemblies in new buildings, it is not always possible to easily verify the provenance or integrity of existing structures, assemblies and components. “Reversible” design can mitigate against these problems by ensuring that any new intervention operates independently of the existing building where possible. |
Timber can be easily
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22 Combined bonded elements could be detailed for reuse as a single element, but this is unusual 23 External insulation systems often bond mineral finishes to the insulation behind, making both re-use and recycling very difficult. Paint finishes also inhibit recycling of aluminium, steel, and wood; mill finishes are preferable for metals where possible and internal woodwork should ideally be finished with wax or natural stains rather than paint. 24 Bioregional Reclaimed is a unique company that specialises not only in re-using steel but also in structurally assessing steel for re-use. 25 For example, Scottish social housing is only replaced
at 1% per year (Stevenson and Williams, 2000) back to top | contents | next chapter
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