As city populations around the world expand at unprecedented rates, a corps of urban thinkers is examining how to add density by building on top of existing buildings, rather than rebuilding cities from scratch. About 25 per cent of the existing buildings, which are mostly masonry structures, in London, England can support additional floors comprised of such lightweight wood products as laminated veneer lumber (LVL), Mike Kane told delegates during a seminar at the Toronto Wood Solutions Fair recently. Kane, a director of London-based KMK Architects Ltd., said tracts of long-established neighbourhoods largely made up of council (public) housing in London proposed to be demolished could be saved by adding wood storeys.