Design for Deconstruction

Design for de-construction

Re-using and recycling building materials is a great approach to sustainable energy because it saves energy and resources as well as diverts materials from landfill. However it is difficult to re-use and recycle building materials without good planning for the deconstruction of the building.

Designing details for deconstruction at the start of a project enables one building, at the end of its useful lifespan, to be the resource for the next and helps "close the loop" for resource use. During the deconstruction of the building, materials of which the building was constructed from is released. These materials will become waste unless it can be extracted and be reused or recycled. Hence, to facilitate the process of extracting the material of the deconstructed building so that the materials can be reused and recycle, one must plan the deconstruction of the building with it's "after-life" in mind.

By designing the building with the concept of "Design for deconstruction", it can tighten the loop of materials use in buildings, assist the transition towards minimal virgin materials use, and proliferate the current paradigm of cradle-to-grave to a more ideal cradle-to-cradle approach.

The greatest barrier hindering the design for deconstruction and reuse/recycling of reclaimed materials and products as follows:
" The cost includes the additional time involved for the deconstruction;
" The difficulty of costing the re-used materials which will be used on different projects;
" The damage caused by poorly designed assemblies and connectors; and
" Limited flexibility of the reclaimed element.

There are many factors to consider in the design for deconstruction of a project. The following sections will discuss three important considerations to consider: materials, assemblies, and building systems. Other strategies will be briefly looked at.

Materials

Current problems in older buildings include:

  • the prevalence of materials that later became environmental hazards for workers and for disposal; and
  • segregating materials without damaging the materials so that they can be reused or recycled

Design Strategies

Things to consider in the design for deconstruction

  • Quality and durability of materials
  • Use materials worth or feasible to recover
  • Minimise number of different materials
  • Avoid composite of dissimilar material
  • Minimise toxic materials
  • List prohibited and preferred materials
  • Minimise material quantities
  • Eliminate the use of secondary coatings

It is important to consider components that are durable enough to be repaired or reused with minimum work and cost as well at to be readily recovered without damage. Components should be designed to maximize the number of times they can be reused.

Where a component or finish is not particularly durable and unlikely to be re-used, it is important that it can be easily recycled. This is easiest if the component is of a single material or can quickly be broken down into individual materials.

By using fewer materials, it simplifies deconstruction. Composite materials are more difficult to separate and hence more hard to recycle or reuse. If more material types are necessary, the interface between the materials should be carefully considered.

Commercially valuable components and materials, with potential for reuse and recycling, need to be identified in advance by means of a pre-demolition building audit. This will have a large influence on how the soft strip and demolition is conducted, for instance whether selectively and with great care, or with less concern for avoiding damage to components.

Segregation is essential to realize the maximum benefit from materials streams produced by deconstruction processes. Designers will be able to facilitate the potential for recycling materials used are capable of easy separation and segregation and further processing to create useful recycled materials. The materials should be carefully managed and stored to avoid contamination and prevent damage.

Buildings that facilitate reuse and recycling will use nonhazardous materials, bio-based materials, high quality and highly recyclable materials.

Two notable examples of recently constructed commercial buildings in North America that relied heavily on recovered materials and were also designed to facilitate future materials recovery are the Phillips Eco-Enterprise Center, Minneapolis, MN, and the C.K. Choi Building at the University of British Columbia, Vancouver, BC.

Assemblies

Lessons learned from the deconstruction of older buildings - well-known to practitioners
in the field - include:

  • the use of connectors that are inaccessible and cause damage in the process of separating materials;
  • the weakening and de-stabilization of a building during the deconstruction process; and
  • how the building assembly process may render materials un-reusable or un-recyclable via drilling, cutting, and use of binders, adhesives, and coatings - especially hazardous materials.

Design Strategies:

The assembly refers to how the pieces of the buildings fit together. Things to consider in the design for deconstruction:

  • Minimise number of components
  • Minimise number of fasteners
  • Use mechanical fasteners in lieu of sealants and adhesives
  • Simplify connections
  • Make connections visible/accessible
  • Separate building layers or systems
  • Distangle utilities or systems
  • Minimize the variety of connection types

By minimizing the number of components and fasteners so that there are fewer but stronger and larger can make the deconstruction of the building easier and can facilitate the reuse of the component. Reversible fasteners should be used so that the material can be easily reused. Irreversible fasteners such as glues and chemicals should be avoided since the may damage the material as they are to be removed. Bolts, screw and mechanical fasteners should be considered. These connections simplify the disassembly process.

Since different parts of the different assembly have different life expectancy, the design should consider the access to the various assemblies and sub-assemblies which need to be maintained, repaired or modified periodically. Connections should be simplified, readily accessible, and where possible exposed to serve as everyday clues as to the deconstruction process, or at least allow users to formulate questions about assembly and disassembly.

Table 1: Evaluation of connection alternatives for deconstruction

Type of Connection Advantages Disadvantages
Screw fixing - easily removable - limited re-use of both hole and screws
- cost
Bolt fixing - strong- can be re-used a number of times - can seize up, making removal difficult
- cost
Nail fixing - speed of construction
- cost
- difficult to remove
- removal usually destroys a key area of element
Friction - keeps construction element whole during removal - relatively undeveloped area
- poor choice of fixings
- structurally weaker
Mortar - can be made to variety of strengths - mostly cannot be re-used, unless clay
- strength of mix often overspecified making it difficult to separate bonded layers
Resin bonding - strong and efficient
- deal with awkward joints
- virtually impossible to separate bonded layers
- resin cannot be easily re-cycled or re-used
Adhesives - variety of strengths available to suit task - adhesive cannot be easily re-cycled or re-used, many are also impossible to separate
Riveted fixing - speed of construction - difficult to remove without destroying a key area of element

(Source: Design and Detailing for Deconstruction - SEDA Design Guide for Scotland)

Modularity and prefabrication can promote reuse and recycling at a larger scale. Modules and components should be dimensioned for reuse. Hence, it makes sense to modularize a particular assembly if it makes construction and deconstruction easier.

Building Systems

Current problems in older buildings include:

  • the entanglement of HVAC, electrical and plumbing systems within walls, floors and ceilings, that impedes the separation of building components;
  • matching the scale of the capabilities of a human laborer to the scale of building components; and
  • Dismantling or upgrading one system can affect another system

Design Strategies:

  • Consider building system relationships, efficiency and articulation
  • Consider independent (self-supporting) assemblies
  • Use standardized building elements and systems whenever possible
  • Specify components with sizes that are suitable for handling and transportation

Extricate systems make it easier to maintain individual systems and facilitates adaptation or deconstruction. Thus, the removal or modification of one system does not affect another. For example, the enclosure, structure, infill, substructure, mechanical and electrical systems can be separately install with no dependency to each other. Moreover, separating systems allow for more flexibility which adequately addresses the environmental impact of materials used, relative to desired permanence or changeability.

Other Strategies

Other deconstruction strategies include:

  • Maximize clarity and simplicity and minimize building complexity;
  • Minimize different types of materials;
  • Minimize number of components (fewer, larger elements);
  • Minimize number of fasteners (few, stronger fasteners);
  • Simplify connections;
  • Make connections visible/accessible;
  • Separate building layers or systems (Extricate systems);
  • Disentangle utilities from structure;
  • Use materials worth recovering;
  • Minimize toxic materials (ease of abatement);
  • Provide access to components/assemblies (windows, etc.);
  • Provided access or tie-offs for work at height; and
  • Accessible information which includes construction drawings & details, identification of materials and components and structural properties
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