Building materials need not be used just the once and
then discarded at the end of a building's life. Reporting
on her recent wide-ranging study, Dr Paola Sassi
examines how to design with one eye on the future.
At the end of a building’s life, it can either be demolished or it can be dismantled and the elements and materials reused and recycled. The most environmentally beneficial use of waste is to reuse it, reuse being associated with higher reductions of embodied energy and emissions to air and water compared to recycling. However recent surveys undertaken by the Department of Environment, Transport and the Regions estimates a minimum of 53 million tonnes of construction and demolition waste being produced annually in the UK, of which 24 million tonnes of inert waste are recycled (recycled and downcycled) and only 3 million tonnes is reclaimed for reuse.
The low reuse and relatively low recycling rates reflect a number of barriers to recycling and reuse including the fact that most building elements are not currently designed for dismantling and the resulting excessive time requirements for dismantling coupled with low disposal costs make dismantling a prohibitively expensive process . Demolition contractors report that deconstruction can take two to ten times longer than demolition efforts putting deconstruction at a distinct economic disadvantage. However economics is not the only barrier to reuse and recycling. Current building codes and certification systems do not generally deal with reclaimed materials and elements and where the element’s performance is not a crucial issue, aesthetics and commercial desirability may be instead. Consequently even if a building material or element is capable of being dismantled from a technical and economic point of view, it still may not be reused or even recycled due to the lack of a market for uncertified products or those of lesser aesthetic appeal.
The study highlighted a number of problem areas, but also showed that there is potential for designing reusable and recyclable structures. The following aspects to consider emerged.
Building elements are interlinked as one layer of the building structure is supported on another. If the installation method of one element precludes its own reuse and recycling it is likely to also preclude the reuse or recycling of the linked elements. Wall and ceiling finishes are prime examples of this affecting the reusability and recyclability of their substrates. While mechanically fixed boarding materials (e.g. timber, plastic) can easily be removed allowing the fixings of the support structure to be accessed and ultimately enabling its dismantling, applied finishes (e.g. plaster, tiling) can make the access to the support structure fixings difficult and in some cases impossible and can also contaminate the substrate material precluding its recycling (e.g. plaster on blockwork).
The composite elements studied often proved easy to reuse, but impossible to recycle, confirming the guidelines produced for designing for recycling that recommend avoiding composite materials.
Materials – Different materials proved particularly suited to specific reprocessing techniques: metals being easily recycled, concrete most easily downcycled and timber easily reused.
Prefabricated elements often rated highly in terms of their reuse potential, but some rated quite low in terms of their recycling potential as the ability to be recycled is dependant on the design of the unit itself, which often included composite material that could not be recycled or downcycled.
Reuse of such products as roof membranes, structural elements or insulation material can be hindered by the lack of certification of the elements’ performance. Provision of information on the building products may partially eradicate the problem, but in certain cases testing will still be necessary adding to the cost of reusing the products. Recycling building elements circumvents the issue of product certification.
Aesthetic barriers can hinder the reuse of building elements. This clearly applies to visible elements and perhaps applies more to internal building elements than to external building elements. The ability to reapply a finish to a product to be reused could prove invaluable in terms of reusing such items as toilet cubicles that are dismantled with extreme ease, but are normally not reused due to their second-hand appearance in a building area where a second-hand look is not considered acceptable. In particular where elements are of standard sizes, such as doors the ability to reapply a finish would make what is an easily reclaimed standard sized item very marketable. Being able to reapply a finish would also address the issue of design fashion, enabling building elements to be upgraded to the current fashion requirements.
The reused potential of building products and elements is affected by the design flexibility afforded by the reclaimed item. Building elements made of small units such as bricks in brick walls or rubber tiles for floor finishes, allow for the units to rearranged to suit different designs. At the opposite end of the spectrum are building elements such as windows or prefabricated wall panels made of different types of units acting together as one, which if reused will dictate what the design will be. This limited flexibility constitutes a substantial barrier to their reuse.
Some areas of building design represent a particular challenge in terms of achieving easily reusable and recyclable buildings, while others already provide a good choice of recyclable products. However there is still a need to refine current designs to accelerate the dismantling process where it is already possible and enable it where it is currently impossible.
On the technical side, building finishes pose possibly the most serious technical and aesthetic problem, as the existing options that enable dismantling are not those traditionally used that appeal to the general public and the aesthetically acceptable options are often not dismantleable. As illustrated in Table 3 a commercial building designed for recycling and reuse may be in part visually indistinguishable from a traditional building designed for permanence, but a domestic building designed for recycling and would appear very unusual.
On a psychological level, a change of mindset is required not only in terms of aesthetics, but also in terms of adopting and promoting reuse and recycling as a truly economically viable and desirable option, not only by clients, but by all the construction industry.
Finally it is often the case that building products can be installed in a number of different ways that differently affect the product’s recyclability. It is therefore through careful specification as well as considered building products selection that a dismantleable and reusable or recyclable building solution can be produced. Perhaps a model specification such as those already in use in the UK (National Building Specification), but one with the purpose of defining and specifying dismantleable, reusable and recyclable buildings would provide the most effective support for designers wanting to ensure maximum reuse and recycling.