DfD Buildings: What is Design for Disassembly?

In the building field, DfD is a design strategy for materials, building components or whole systems where such components can be reused when a building is deconstructed.

Why use DfD?

Compared to traditional building design, DfD uses resources more efficiently.

Therefore, it generates fewer environmental impacts caused by extraction, processing and manufacture of resources.

Moreover, the embodied energy and CO2 emissions are significantly reduced by disassembling and recycling building elements.

Based on the ATHENA Life Cycle Assessment [LCA] model, Morrison Hershfield Engineering has concluded that reusing every cubic meter of precast double-T concrete benefits:7

• 1.23 GJ less energy
• 147 kg CO2 reduction
• 50% water reduction [compared to a new double T]

According to the EPA, CO2 is the primary greenhouse gas and its concentration has a direct relationship to global warming.

How does DfD Work?

According to Stewart Brand 6S theory, building is consisted of six S layers and each layer has different life span. As Figure 1 shows.

Figure 1: Stewart Brand’s 6 S’s from How Buildings Learn

A wood-framing structure may last 60 years, for example, whereas a residential roof (skin) lasts 20 years. That is to say, that at the roof’s end-of-life, the structure is still functional. Thereby, a roof designed for “DfD” should allow an easy separation of building structures from the roof when resurfacing the roof.

The service layer contains the building’s electrical wiring and HVAC system and plumbing, which feeds the building its energy, heat, ventilation, air conditioning and water. If such systems are joined together with the structure in a way that makes them problematic to detach, such an effort would shorten the lifespan of the structure because HVAC usually need to be replaced every 15 years while building structure can remain another 50 years.

It is not uncommon that replacing “Services Layer” may require demolishing the entire building.

Strategies

• Simple building structures provide consistent beam sizes and connection types, which can help make them easier to dismantle efficiently.
• Separate building systems make for easier deconstruction. Ideally, when one element in the systems is removed, other elements should remain intact to have a longer useful lifetime.
• Non-toxic, non-hazardous and durable materials ensure the feasibility of those materials for reuse for other purposes.
• Original building drawings and other documents such as materials labeling can be very invaluable when it comes to disassembly.

Restrictions

• DfD may result to higher initial design and construction costs due to the strict material selection and preparation considerations.
• Durability concerns of the salvaged materials, such as strength and stiffness of reused wood members need to be graded and tested.
• Reused materials can bring risk of contamination of other materials. For example, lead paints and asbestos found on recycled steels should be removed prior to reusing.

Case Study

NASA Sustainability Base is an innovative 50,000-square-foot office structure located at Mountain View, California. As Figure 2 shows.

Designed by architect William McDonough, the iconic crescent-shaped building was inspired by the wind tunnels of NASA Ames Campus and satellite.

Figure 2: The interior of NASA's Sustainability Base

In the process of building the NASA base, most of the materials were chosen to be recyclable or recycled. Additionally, fewer amounts of materials were used.

For example, lightweight insulated metal was used for the external frame in order to reduce the amount of steel used and recycled white oak flooring was used for the interior. Also, the structure was designed for disassembly, so it could easily be dismantled in the event of an earthquake.

The NASA Base is designed to be “Net Zero” energy positive building (Zero Net Energy Building), or a building that generates as much if not more energy than it consumes.

The cradle-to-cradle concept promotes regenerative design for nature and human benefits, which allows the surrounding environmental elements to blend into the building.

Figure 3 shows the building’s exoskeleton structure and orientation provides a column-free interior to ensure no artificial lighting is needed during working hours, which greatly cuts energy consumption, therefore reduces the CO2 emissions.

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References:
http://www.peterme.com/archives/00000323.html http://www.sabmagazine.com/blog/2009/10/27/design-for-disassembly/ http://www.sustainablebusiness.com/index.cfm/go/news.display/id/24940 http://www.examiner.com/article/nasa-s-sustainability-base