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Photograph: CLERESTORY CROWN Great Hall roof dropped 2 in. in 1992 under a heavy snow load.
THOMAS H. HENRY FOR THE JOHNSON FOUNDATION
Photograph: SURGICAL DEMOLITION Crew extracts old Z-rafter following a 40-step sequence.
VINCI /HAMP ARCHITECTS
Photograph: ZIGZAGS Mock-up for trial runs to take out rafter without harming to finishes.
PHOTO BY VINCI /HAMP ARCHITECTS;
Illustration: Diagram: STEPPED Rafter removal sequence, color-coded and numbered to match roof section, was written in advance. It included 20 major steps, 20 substeps, each with selected tools, and a quality assurance checklist. Roof plan is elongated octagon.
Photograph: ADDS UP Epoxy-impregnated composite material is layered to form diaphragm.
PHOTO BY VINCI /HAMP ARCHITECTS
Photograph: TILE TIES They made fewer holes in roof.
PHOTO TOP BY VINCI /HAMP ARCHITECTS;
How many industries, technologies, tests, consultants, contractors and years does it take to keep high the deformed roof beams of a 3,000-sq-ft room? As many as needed, says the owner, when the room in question is the Great Hall--the crown jewel of Wisconsin's Wingspread, Frank Lloyd Wright's largest and last Prairie House.
``We used the unusual and stretched the boundaries of engineering'' because of the ultimate cost associated with disturbing the landmark, says R. Scott Weas, the agent for the owner-occupier, the Johnson Foundation, in Wind Point just outside Racine. ``Finite-element analysis is not normally used on a house,'' he adds, nor are sailboat composites and aircraft aluminum.
Declining to reveal costs, Weas will say that the foundation made ``a significant investment'' in the rescue to ensure a ``higher probability of success.''
Professional services alone ate up some 30% of the budget. The team, including an architect of record, two preservation architects, a structural engineer and specialists as needed, spent six months investigating. Then the general contractor joined in to help diagram 40 steps for the precision removal of a zigzag roof rafter, 11.5 ft end to end, so that the work would not ruin the historic plaster and wood interior as close as 1/8-in. away.
The now-14,000-sq-ft mansion, completed in 1939 for the Herbert F. Johnson family of Johnson Wax Co., has been used as an educational conference center since the early 1960s. In 1992, on the heels of retiling and reglazing,...