The concept of Design for Disassembly (DfD) has emerged in recent years but the application of it to buildings remains challenging.
Currently, many building materials are not reusable. Materials are often interconnected in ways that make them difficult to separate and reuse even if they are theoretically reusable. The long lifespan of buildings makes it difficult to predict which materials will have salvage value and what technologies will be available to extract materials at the end of the building’s life. Mainstream green building rating systems such as LEED includes incentives for steel scrap sales, but not for DfD.
However, the environmental benefit is certain. New construction, maintenance, and renovation of buildings account for 40% of the world’s material flows. Reuse is the most desirable environmental option because it is most effective in reducing the demand for virgin resources and reducing waste. By reuse or salvage, we mean the reuse of a previously used item (e.g. steel column) with minimal processing, as opposed to recycling where a used product is destroyed to manufacture a new similar or different product.
Improving the odds for material reuse starts when a building is designed, with the building’s full lifecycle in mind. It means designing for durability and adaptability, and designing a building so that it can be efficiently mined as a source of reused materials for new construction when it reaches the end of its useful life. Even if a small increase in materials may be needed at the forefront, DfD should always be a design consideration, while not necessarily the overriding consideration.
Pre-engineered steel buildings (PEB) are 100% re-usable and recyclable. The PEB structures can be easily dismantled to either relocate the building, repurpose for other buildings, or sold as steel scrap that can be 100% recycled.
Characteristics of pre-engineered steel buildings that support the Design for Disassembly principle:
1) Bolted Connections
Bolted, mechanically fastened structures and building materials are preferable to adhesives as they are easily separable into reusable components. On the other hand, composite materials are a difficulty unless the composite assembly has reuse value as an assembly.
2) Avoidance of Composite Systems
It may not be possible to disassemble certain types of composite construction. Detachable, bolted or clamped fasteners on precast elements are preferable e.g. precast decks.
3) Common Building Shapes
Common building shapes allow for regular and repeating patterns in building design, and the leverage of similar building systems and materials throughout the building. This also includes designing with regular spacing. On the other hand, non-standard, custom components for complex building shapes may have no use in any other buildings.
4) Simplicity
Building systems and interconnections that are easy to understand and visible, with a limited number of material types and component sizes, makes it easier to identify and adds value to the disassembly process. For example, PEB structures leverage on only three grades of steel material, making it easy for sorting and identification after dismantling. 345 mpa grade for built-up structures, 245 mpa grade for hot-rolled sections and 450 mpa grade for cold-form sections.
5) Limited Number of Components
Generally, it is easier to dismantle structures that are composed of a smaller number of large members rather than a larger number of small members. Larger members tend to resist damage better during the deconstruction process and can be removed more quickly from the structure.
6) Labelling and Product List
Labels showing product, steel grades, shape/size designations on structural members simplifies sorting and identification efforts and increases resale value. Product Lists with the key product specifications and quantity can be entered into a material bank database for reference in future.
