Four buildings on the Fairfield Hills campus in Newtown are slated for demolition over the next decade, unless developers come forward with viable alternate plans.  The cost to tear down Plymouth Hall, Stamford Hall, Norwalk Hall and Cochran House is estimated at more than 10 million dollars.  The brick buildings are deteriorating and contain hazardous materials so they are not candidates for redevelopment.  Developers plan to use federal tax credits to build age-restricted housing in two other old buildings--Kent House and Shelton House.  Boston-based Winn Development also plans for some commercial uses in the structures.  The Planning and Zoning Commission still need to sign off on plans. Stratford House was redeveloped into the NewSylum Brewing Company.  One of the former psychiatric hospital's duplexes was converted into the headquarters of a non-profit.  The last building on the campus to be demolished was in 2016, to make way for the Community Center and Senior Center.