Construction and Demolition Case Study: Presidio of San Francisco

Site Visits

The following chronology of the deconstruction of Building 901 is based primarily on four site visits to this project by the staff of the California Integrated Waste Management Board. The observations and conclusions noted by staff are as follows:

April 4, 1996

Staff from CIWMB first visited the site of building 901 on April 4, 1996 to document the deconstruction and salvaging techniques used on the building. At this point, remediation for the removal of lead-based paint and asbestos had already occurred. Hazardous materials removal by qualified professionals is necessary prior to commencement of any demolition activities.

4/4/96:  Building 901.  Roofing material removed exposing rafters.	4/4/96: 6"x6" supporting posts throughout Bldg. 901.

This first visit revealed that deconstruction activities were already well underway. As shown in the adjacent illustration, some of the siding and the majority of the roofing material was already removed, revealing the roof joists. The majority of interior sheeting had also been removed.

Although the siding had been scraped to remove loose lead-based paint, the majority of exterior paint remained on the wood. In the past, demolition operators have questioned the logic of scraping and removing loose paint only to have far more paint loosened during disassembly of the structure. No resolution to this issue has yet been developed.

The siding on building consisted of tongue-and-groove (T&G) redwood. In order to reuse the painted siding, which is coated with lead based paint, the boards will have to be turned over, exposing the unpainted side, or the wood will have to be remilled, adding to the cost of the final product.

Other exposed sections of the building revealed that the roof rafters were 14 and 21', 2" x 6" lumber tied together to span the entire length to the ridge pole of the building.

The flooring was still intact during this visit, but the crew expected it would be difficult to remove because it was constructed of 2" x 8" T&G that was toe-nailed down. This makes it very difficult to remove the boards without splintering the wood. The floor was supported by 2" x 12" joists and the roof was supported by 6" x 6" posts throughout the structure as illustrated in the adjacent picture.

The crew was carefully recovering as much lumber as possible from this structure. The economics of this project have been modified somewhat by the fact that the entire job falls under federal prevailing wages as dictated by the Davis-Bacon Act. As a result, the laborers, by law, must be paid federal prevailing wages on site. This translates to about $25 - $35/hour which is above what is normally paid to salvagers on a non-federal deconstruction job.

The crew was given four weeks to dismantle the building. The work was progressing well and they anticipated completing the job in three weeks.

At this point in the deconstruction, wood was removed and stacked with similar dimension and type lumber. The wood that was denailed was stacked and looked ready for sale.

The windows were removed in their casings and were to be sold as whole units. Older wooden frame windows sell for $5 to $20 depending on the size and condition. There seems to be a fair demand in the San Francisco Bay area for this type of window, mostly from local artists, and cabinet makers, or for replacements in many of the older buildings in the area.

The exposed interior walls revealed the difficulty in removing the drywall. The abundance of nails and remaining adhesives indicated that this was a very labor-intensive job. These aspects of a job are not always obvious at first inspection.

The studs that were recovered were generally grade 1 and clear. The wood is also quite dense. This is an extremely high quality wood considering that most of the studs pulled so far are nonstructural. When there are knots in the wood, they are quite large, indicating that they came from old growth stock. These knotty elements would not pass today's grading standards for construction lumber. Some of the framing material pulled from the interior is redwood. This came out of one of the offices added to the building interior.

Phil Kreitner, of the Wood Resource Efficiency Network, indicated that he hoped to get about $1/board foot (bf) for the wood. This is comparable to prices for lumber found at a local home improvement center. In order to demand this premium price, the materials will need to be marketed as old growth stock, which is denser and stronger than today's lumber, or associated with the Presidio to inform the buying public that this material differs from normal lumber.

April 12, 1996

The deconstruction had progressed significantly from 8 days earlier. The building was stripped down to the bare framing material. The floor boards remained intact at this juncture of the project. Most of the wood that was removed was denailed and stacked according to size, type, and shape in neat piles on the surrounding lot.

4/12/96: Crew is in the process of removing rafters.	Alternate view with Golden Gate Bridge in background as a reference point.

The recovery of the clean lumber is quite labor intensive due to the inordinate amount of nails and fasteners that were used to adhere the redwood siding to the building. In addition to removing the wood without damaging it, a great deal of time must be spent removing these fasteners.

One advantage that this particular project presents is that the site of building 901 is serving as an ad-hoc lumber yard. The consortium will try to maximize this aspect of the job and sell as much material on site to the public which will reduce transportation costs. Any remaining lumber will be divided between San Francisco Community Recyclers, Beyond Waste, and Wood Resource Efficiency Network to be sold at a later date. The crew expected to have the building totally dismantled within another week.

April 24, 1996

Again, the project has progressed significantly since staff's last visit, in spite of rain that reduced the number or working days.

The building had been dismantled to a point where it no longer is visible from any distance. All the framing has been removed, denailed, and neatly stacked on the surrounding lot. The wood was sorted by size and type. The majority of structural wood consisted of douglas fir studs of grade one or structural select with some redwood studs coming from the walls of an interior office. A few grade two studs were found in the interior walls. The ceiling studs and exterior siding were redwood and some pine was recovered from the wall planks and a few studs.

4/24/96: Lot starts to look like a lumberyard.

The crew was removing the remaining portions of the flooring during this site visit. Of the original floor, approximately one-third of the floor joists remained and one-fourth of the T&G floor boards were still in place. The concrete walls that support the floor joists are about 6 inches wide, 2 feet tall, twelve feet apart, and run the length of the building.

As anticipated, removal of the floor boards was labor intensive because each board was toe-nailed in. To expedite removal without damaging the lumber, the crew ran electric reciprocating saws, powered by gas generators, between the boards and the floor joists to cut the nails. The boards were then lifted using a tool that looks like a horseshoe welded at a right angle to a pry bar (as seen in the adjoining photo). The flooring itself is 2" x 8" stock running in lengths of 12' to 24'. The crew was unsure of the type of wood that made up the flooring. It was guessed at the time, that the flooring may have been sugar pine or cedar, and was later determined to be Port Orford Cedar.

4/24/96: Crew cuts nails with electric saws and pries up floor boards.		Crew removes joists after T&G floor is pulled up.

The remaining third of the flooring was covered with mastic residue from the removal of asbestos tiles that covered the office area inside the building. To reuse the wood that made up this portion of the floor, the boards will have to be turned over, exposing the unfinished side, or remilled.

Phil Kreitner informed staff on this visit that an additional 4000 board feet (bf) of decking was sold on site for $1/bf.

The work completed thus far had taken 15 working days. The crew felt confident that the job would be completed close to the original estimate of four weeks.

May 10, 1996

CIWMB staff did not return to the Presidio until May 10. The final disassembly and salvaging of building 901 occurred some time between April 24 and May 10. The only evidence that a building existed was the vacant lot and stacks of lumber still remaining on site (illustrated in the adjoining photo).

5/10/96: Nothing but a vacant lot and a view of the Golden Gate Bridge.		The remaining lumber will be sold off site.

As the photo of the vacant lot above illustrates, the concrete walls supporting the building were broken up and removed. This portion of the project was performed by a separate contractor.

Approximately half the lumber recovered from building 901 was sold on site. The remaining lumber was divided between San Francisco Community Recyclers, Beyond Waste, and Wood Resource Efficiency Network to be used or sold at those sites.

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Last updated: October 21, 2007