Design and Detailing for Deconstruction

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5 Deconstruction Detailing Principles

5.1 Adaptability
5.2 Layering
5.3 Access
5.4 Connections
5.5 Durable components
5.6 Structure
5.7 Insulation & airtightness
5.8 Skins
5.9 Services
5.10 Key construction materials: re-use potential
5.11 Risk & safety issues
5.12 Existing building stock

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Key Principles

1. Design Buildings to be adaptable to different occupancy patterns in plan, in section and in structural terms.

2. Ensure that buildings are conceived as layered according to their anticipated lifespans.

3. Ensure all components can be readily accessed and removed for repair or replacement.

4. Adopt a fixing regime which allows all components to be easily and safely removed, and replaced through the use of simple fixings. Design connectors to enable components to be both independent and exchangeable.

5. Use only durable components which can be reused. Try to use monomeric components and avoid the use of adhesives, resins and coatings which compromise the potential for reuse and recycling.

6. Pay particular attention to the differential weathering and wearing of surfaces and allow for those areas to be maintained or replaced separately from other areas.

7. Carefully plan services and service routes so that they can be easily identified, accessed and upgraded or maintained as necessary without disruption to surfaces and other parts of the building.

5.1 Adaptabilty

Aiming to design buildings to be adaptable will tend to lengthen their service lives, and so minimise the energy and resources required over that period. Current practice for most buildings is based on a 60 year lifecycle. This is very short when one thinks of previous generations of buildings that have stood easily for 200 years or more.

An important consideration is layout. The image below shows the same tenement block arranged in three different ways, allowing for three different occupancy patterns, with the minimum of alteration required. Occupancy patterns change and such layouts make it cost effective to react to changing markets, considerably extending their useful life.

For such layouts to work, the planning of the building has to be carefully considered. Zones of similar function should be grouped and the structure kept simple, impinging as little as possible on the internal arrangements. Serviced areas such as bathrooms and kitchens need to be strategically positioned, or allowed for, in order to anticipate change, as well as connection options between rooms.

The golden rule is to anticipate change, and to design buildings that make such changes easy to achieve. The logic of this approach has been developed in the UK particularly by the emergence of “Lifetime Homes” [21] which address the changing needs of building occupants.

Even at individual room scale, design can anticipate and allow for future changes of use, as shown below through the size of room, and the location of doors and windows.

Buildings such as this tend to be built to standardised grids and fairly simple geometries. Adaptability is also a function of other aspects such as structural layout and layering of the construction, as discussed below.

5.2 Layering

Different parts of a building perform different functions and have different lifespans. Much of the waste arising from construction comes not from demolition of complete buildings, but from incremental processes: refurbishment, upgrading, fit-out changes to reflect organisational changes, wear and tear or weathering and components reaching the end of their service life.

These processes generate considerable and unnecessary waste either because the components were not really worn, or unwanted, or because the buildings are designed so that not only the component itself, but several adjacent and connected elements have to be removed.

Each “layer” of a building has a different life span (after Steward Brand, 1994) Source: Chris Morgan

Stewart Brand, in his book “How Buildings Learn” offers a helpful conceptual framework for dividing the parts of a building into these different lifespan elements. Each layer performs a different function, and can be expected to last a certain time before replacement. Those with faster replacement cycles are closer to the surface, more easily accessed, and able to be removed from more permanent components beneath without undue disruption or damage.

For the sake of faster site construction, pre-fabricated elements are sometimes used where main structure, insulation, and finished skins are bonded together in a single piece. Unless they are demountable, such assemblies are subject to the weakest link in the chain – the least durable element – failing, whereupon the entire piece may need replacement, often at a higher cost than the simpler repair or maintenance of just the outer cladding, for example.

5.3 Access

Lack of adequate access is one of the single biggest inhibitors of successful deconstruction. Access to elements for repair and removal may be considered in three ways.

1. Sequential access:
Sequential access this is discussed in the section above on layers. Access is strategically poorly devised if a more permanent element is in front of the one requiring attention or removal.

2. Physical access:
This means being able to reach a component and remove it safely and completely. Generally, the larger the construction element, the more room there is required for deconstruction and removal. Large elements which are too heavy to be lifted by workers, but to which access by a crane is impossible, are an example of physical access problems to avoid.

3. Access to fixings:
If the fixing to a component is behind it and not accessible, then much more work will be needed to remove it. Often, there is simply not enough room left for construction workers to be able to manoeuvre with appropriate tools in order to remove elements by unfixing them. Some components require a special tool to be dismantled, which needs to be nearby and marked, and a spare kept just in case. Some components have many fixings visible, where only one is needed to remove it, but is that particular fixing marked?

Planning and detailing for deconstruction should be checked in terms of access and ensuring that whole construction elements can be successfully removed from the building through identified access routes, especially where anticipated lifespans are shorter. This should be linked to the Health and Safety Plan.

Make sure prefabricated
panels can be re-used
and recycled at the end
of their lifespan
Source: Trada

Elements should be kept
small enough for easy
manual replacement
where possible.
Source: F. Stevenson

5.4 Connections

The design of connections is arguably the single most important aspect of designing for deconstruction. The type of connection used between construction elements will determine whether or not it can be successfully deconstructed (see table 2).

Connections come in three categories in terms of how they interface with components:

• direct connectors
  
• indirect connectors
• infilled connectors
  

Direct connectors usually interlock or overlap with components, which can make deconstruction difficult due to the assembly process. Indirect connectors are usually easier to deconstruct because they are interchangeable and independent from the components. Infilled connectors such as glued or welded connectors can be virtually impossible to deconstruct unless the filler is very soft, such as lime mortar.

Connectors should always be designed to enable components to be both independent and exchangeable. Equally, the geometry of the components’ edges in relation to the connection design will dictate whether or not components can be disassembled.

Plan section of a direct
connector for wooden
panels

Plan section of an
indirect connector for
wooden panels.

Table 2: Evaluation of connection alternatives for deconstruction

The best fixings are those which are themselves durable, and help to preserve the structural integrity and finish of the construction elements to be joined, during the process of deconstruction.

The use of notching, cutting and holing should be avoided where possible and the designation of “fixing free zones” can help maximise opportunities for re-use of lengths of material. Friction jointing is the least disruptive form of fixing and highly desirable for structural elements which may be re-used. Examples of friction joints include timber-on-timber sleeve joints, clamps and pre-formed sockets for receiving elements.

Two key criteria for designing connections which can be disassembled while maintaining the integrity of all elements are:

1. Avoid interpenetration of connectors with components
2. Adopt dry-jointing techniques in preference to chemical jointing

Try to minimise
interpenetration of
connectors with
components
Source: Trada

5.5 Durable Components

For the potential of deconstruction strategies to be realised, and for waste arising from construction to be reduced, it is important that the components that can be readily recovered without damage are durable enough to be repaired or reused with the minimum of work and cost.

Component lifecycles for buildings, such as windows, doors, panelling and roofing are calculated on the basis of 10 - 25 years. This is a relatively energy-intensive and short cycle when one realises that many Victorian buildings still have their existing components. “Patchable” construction detailing allows elements such as doors, windows, finishes to be easily maintained through partial rather than wholescale replacement.

Components should be designed to maximise the number of times they can be re-used. This requires careful consideration of the durability of the edges between the connector and component. The more robust the edges, the more likely the component and connector can be re-used again and again. Dry-joint techniques that avoid excessive pressure on either component or connector are likely to be the most successful, particularly if the fitting is simple.

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.

5.6 Structure

The structure of a building is designed to carry the primary live and dead loads, as well as resisting lateral forces such as wind. It is the most permanent feature of any building and should be designed to allow for the greatest number of possible occupancy scenarios so as to enable the structure of the building, at the very least, to be useful (and therefore kept out of the waste steam) for many generations to come. There a number of ways this can be achieved.

In the first instance there should be a sufficient floor to ceiling height to enable the widest possible range of anticipated uses. Suspended floor and ceiling structures can make up the difference as required.

The number of internal columns or walls, which could compromise the potential of the building to be used for different functions in the future, should be minimised. For this reason, frame structures with sufficient resistance to lateral force within the frame are to be preferred to panel or solid masonry buildings where bracing tends to be achieved by cross walls, which can reduce long term options for occupants. There are however many masonry and panel buildings which are well used where they are generous enough.

There are generally three primary types of building structure: Masonry, Frame and Panel. The relative advantages of each with regard to deconstruction issues is given in table 3.

Friction jointing is the
least disruptive
form of fixing
Source: Trada

Diagram of a patchable
door element showing
panels that can be
replaced

Diagram of a
non patchable door
element with single panel

Masonry structure
Source: N. Verow

Table 3: Evaluation of structural alternatives for deconstruction

Frame structure
Source: F. Stevenson

Pre-fabricated composite
panelling structure
Source: Trada

Large scale structural sections need complex dismantling equipment on site but offer the advantage of maximising possibilities for re-use especially when standardised. On domestic buildings it may be preferable to have a number of smaller standardised structural elements to perform the same task and allow for easy disassembly.

Footnotes:

21 see www.jrf.org.uk/housingandcare/lifetimehomes/

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