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the limited vertical clearance provided be- neath the raised or relocated structure. Al- though it might be possible to move an ele- vated structure onto an already constructed foundation of driven piles, it would undoubt- edly be extremely difficult and expensive, as would building a new foundation to fit the under surface of an existing slab prior to moving the slab into place. Attachment of the old slab to a timber pile foundation would also present difficult problems. The usual practice, therefore, is to move the structure to the desired location and elevation, and construct the new foundation beneath it. Reinforced concrete or concrete block are the most commonly used construction materials. Other than the restrictions on materials dictated by the presence of the structure overhead, foundation design considerations would be no different than for new construc- tion. Although intended primarily for use in coastal high hazard areas, excellent informa- tion and recommendations on design of foundations for elevated structures is con- tained in the document Coastal Construction Manual published by the Federal Emergency Management Agency. 3 This document, pub- lished in February 1986, is the second edition of the publication originally entitled, Design and Construction Manual for Residential Buildings in Coastal Hil!h Hazard Areas (Coastal Construction Manual), published in January 1981. The publication suggests a number of foundation types and materials suitable for construction ofraised structures in coastal high hazard areas. Several of those suggested would lend themselves to construction in the restricted space beneath a raised or relocated structure. Among them are reinforced con- crete or reinforced masonry unit (concrete block) piers on spread footings, or on grade beams under concrete slabs; and reinforced concrete or reinforced masonry unit shear walls parallel to the likely direction of flow of flood waters or waves. In any case, design of the new founda- tion should consider wind and wave forces, and the potential for erosion and scour. Also, in coastal high hazard areas, careful attention should be given to the connections between the new foundation and the raised slab. The design should take into account the fact that the original slab was intended to be continuously supported on the underlying soiL Unsupported spans of floor slab should probably be limited to 10 feet or less, and piers should be spaced as required to insure integrity of the slab. COSTS INVOL VED 1. Elevating the structure. Costs include site preparation, excava- tion and tunneling, removal of unwanted slab areas, utility disconnections (and temporary flexible connections if required), jacking and leveling, utility reconnections, and site clean- up. Information from structural movers expe- rienced with the process indicates the basic cost of these procedures would be about $12.00 per square foot of foundation area for a 1,200 to 1,800 square foot one-story resi- dence. Costs per square foot would increase somewhat for either smaller or larger struc- tures, and for multi-story structures. There is a practical lower limit to the time required, and therefore the cost, for initial site prepara- tion, excavation and jacking, and for mobili- zation costs, all of which increase the cost per square foot for the smaller structures. Larger structures require more time and labor for the increased volume of material to be excavated. Within limits, up to 10 to 12 feet, the height the structure is to be elevated does not sig- nificantly affect the cost. Costs are affected, 6