Construction and Demolition Case Study: Presidio of San Francisco

Conclusions

Each deconstruction project will be unique and have to be evaluated for the materials that will be generated, the local markets, labor costs, time frames, and overall feasibility. However, this project has yielded some general conclusions that can be applied to any proposed project.

Cost/Benefit

This project clearly shows that hand deconstruction can be performed at rates competitive with mechanized demolition while recovering valuable material, preserving natural resources, and conserving available landfill space. Depending on the structure and situation, hand deconstruction and salvaging can be more economical. This particular building yielded a great deal of high quality, clear, old-growth wood, which is not readily available and will always be in demand. As such, the project was profitable even at prevailing federal wages. If this project had taken place on a non-federal site, or ownership had been deemed to a non-federal entity, the wages paid to the workers would probably be closer to private laborer wages. However, the cost/benefit analysis is somewhat skewed by the National Park Service supplement. It is also difficult to say whether the demolition contract give-back is an accurate estimate of the cost to demolish the structure. Furthermore, the amount sold and price obtained for the remaining lumber recovered from the building would ultimately dictate the final profit of the project regardless of the supplement provided by the National Park Service.

Worker Experience

The crew's ability to salvage material without destroying it in a timely fashion enabled the project to achieve a high recovery rate and in turn, maintain its cost effectiveness. If a project is being proposed that involves hand deconstruction and salvaging, it is imperative that professionals with salvaging experience be sought out. Experienced demolition operators are not always the best choice for salvage operations. If a project is to achieve a high rate of recovery, the operators chosen must have knowledge and/or experience in the non-destructive recovery of building materials, not just demolition experience.

Define Rate of Recovery

When proposing a job with the intent to reuse or recycle a high percentage of materials generated, a minimum rate of recovery should be specified and terms such as "recover" must be well defined. This project salvaged a high percentage of lumber for reuse. Of the 15 percent of the wood not recovered, a portion was being ground by wood processors. If terms are not defined in the contract, the grinding of wood waste can be defined as recycling and meet goals stated in the contract without meeting the intent of the project. Define terms such as recycle and reuse to ensure that intended goals are met and that there is a level playing field for contractors bidding the project.

Time Frames

Deconstruction or "soft demolition" techniques generally take longer than mechanized demolition operations. In order to salvage building materials, additional time is usually needed. This must be accounted for when planning a salvage operation in lieu of a mechanized demolition operation.

Storage Needs

Additional storage areas may be necessary if high percentages of materials will be recovered. In the case of building 901, the surrounding lot was fenced off and served as an ad-hoc lumber yard, which enabled the crew to sort and stack material according to size and type. This, in turn, fostered the on site sale of over half the lumber recovered from the building. Beyond generating immediate revenues and allowing the local community to purchase desirable materials, it reduced shipping costs.

Project Summary

There were two factors, specific to this project, had they been altered, could have influenced the overall profitability of the project. The first factor involves contract negotiations. The overall demolition contract was amended to include the deconstruction of Building 901. Since this aspect was added to the contract after the fact, it is reasonable to assume that the proponents of the deconstruction project were not negotiating from a position of strength. As such, they may not have been able to negotiate the most economically desirable contract. However, it is difficult to determine how great an influence this had on the final agreement. Regardless, it is safe to say that it is far better to incorporate all reuse and salvaging aspects of a project into the contract in the beginning rather than reopen the contract to negotiations later in the process.

The second site specific factor that may have influenced the overall economics of this project involved assessment of the value of the recovered materials. In general, the consortium was quite knowledgeable about local markets and the materials that they recovered. However, in retrospect, they did indicate that the Port Orford Cedar recovered from the flooring could have probably been sold at a higher price due to it scarcity. It is inconclusive how high a price the market would bear for a material such as this and it is probably best to file this aspect under lessons learned.

It should also be noted that remediation of asbestos and lead based paint occurred prior to deconstruction and was not part of the economic analysis. Any project being proposed should consider any additional costs associated with the remediation of hazardous materials. In general, the military will remediate materials that are hazardous and that have an exposure pathway from any structures prior to conveyance. However, this may not address all asbestos and lead based paint that may be exposed during a deconstruction or demolition operation. Only a site specific analysis could determine if costs for remediation of hazardous materials at a deconstruction project would differ significantly from remediation costs at a mechanized demolition project.

The site-specific issues discussed above, as well as the general issues discussed in the previous sections, may need to be considered when evaluating the economic benefits of choosing deconstruction and salvaging of a structure over mechanized demolition. However, if thoughtfully planned, a deconstruction project can yield significant income (as illustrated in the table), as well as save disposal costs, virgin resources, and valuable landfill space.

This case study would not have been possible without the information and ongoing assistance provided by representatives from the National Park Service, Beyond Waste, San Francisco Community Recyclers, and Wood Resource Efficiency Network.

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Last updated: November 01, 2007