The City has said they have no details to support the $7.2 million estimate . In my opinion, that number is a ball park number and a NEW (not retrofit) City Hall can easily be built for $4 Million ( $465.sq.ft). A year ago (2/9/19), I submitted a $4M-$5M estimate to the City Council. (A 8,600 sqft building for under $5M at $581/sqft is doable.)
New construction is more predictable, standard details to codes are already developed, etc. The problem with NEW? Architects and owners get carried away building a “signature thing”, running costs up. If an architect targets a $465/sqft project (which includes 45% for design soft costs and contingency), then it’s done. The City hires them to design to that standard. Then, the City holds back another $1 million (“risk management control fund”). The City Council would vote on whether to dispense risk money from this fund ( e.g. retaining the original exterior walls are such a risk).
Tighter control on cost can be obtained by separating the demolition contract from the construction contract. This allows the construction bid to evaluate the site and limits “differing site conditions” as a reason to “claim“ after construction begins.
New construction can be much faster and less disruptive than retrofit. Contractors in San Francisco routinely gut the entire building, support the exterior walls in place and build the new structure inside out. Often, they open up the end of the building and drive loaders and bobcats in and out to demolish and build new.
Ted Hall P.E.