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Benefit Cost Analysis Building Costs Table 1 delineates the construction costs associated with each building type, Costs are presented in terms of total building costs, per square foot costs, and average annual costs, The increased costs associated with flood proofing are highlighted, The detailed cost estimates from which these data were drawn are included in Appendix D, The total construction cost for the basic building is esti, mated at $562,812 or an average annual cost of $52,398 over a 20 year period, On a square foot basis these costs total $25,01 or $2,33 annually for the 20 years, For the wet flood proofed building, the two major addi- tional costs are for glazed concrete block partitions in lieu of metal studs and drywall ($14,400) and the pre, mium for installing a waterproofed pit and a hoistway type elevator and associated penthouse in lieu of a hydraulic elevator ($1 0,000), Such wet flood proofing adds $46,915 to the cost of the total structure, or $2,09 per square foot (when dispersed over the total square footage of the building), Since many of the flood proofing costs are incurred only for the ground floor construction, the taller and larger the building, the less flood proofing adds to the square foot cost of the building, For the building raised to one foot above the base flood on fill, the two major added costs are for the imported compacted fill material at $3.50 per cubic yard (a total of $12,530) and the addition of curved approach ramps with handrailings and retaining walls ($9,000), This method of compliance with the minimum rules and regu' lations of the National Flood Insurance Program adds $35,912 to the cost of the total structure, or $1,60 per square foot. For the partially raised building with watertight closures the primary added cost is for a 30 inch mat slab on fill in lieu of the 6 inch slab on grade ($33,750), The other relatively major cost is for a three inch layer of trowelled asphalt waterproofing below the mat slab ($11,250), The actual bulkheading adds only a $5,000 cost to the struc- ture, Overall cost is increased by $89,732 or $3,99 per square foot. When the building is elevated to 6 feet above the base flood on columns, certain cost items are added, but others are subtracted, The largest addilional cost is for the metal pan formed concrete suspended slab, includ, ing formwork, bracing, reinforcement, and finish ($41,250). Other major costs are for: extending the core area to the parking area at the ground level, including stairs and elevator extension ($20,000); installing a 18 waterproofed pit and hoistway type elevator with asso- ciated penthouse in lieu of a hydraulic elevator ($10,000); and providing more expensive foundations ($10,000), Costs which are deducted from the basic structure, on the other hand, are for the slab on grade ($12,000) and one set of entranceway stairs ($5,000), Overall, the cost olthe structure is increased by $87,923 or $3,91 per square foot. For each of the elevated struc- tures, the additional cost per square foot is also reduced when costs are dispersed over a larger building, even though the costs of elevation, when spread over the greater square footage of the large structure, would decrease, In terms of additional construction cost, therefore, raising on fill is not only the least costly method of flood proofing, it also complies with the minimum regulations for the proposed building at the Jersey Shore site, There are several reasons why raising on fill was the least costly flood proofing method in this instance, The site is in an urban renewal area in which debris is mixed with a primarily sandy soil. Since compacted fill provides a better soil condition, raising on fill reduces foundation costs, In addition, the structure is iow,rise; raising on columns is not as economical because the cost cannot be dispersed over a large building, In other locations, for example where open space and parking areas are at a premium, there might still be an economic incentive for elevation on columns that leaves the ground level avail- able for other uses, In Jersey Shore, where the density of development is low and land is available and relatively inexpensive, such incentives are not present. Equipping the building with watertight closures was more costly, primarily because waterproofing the foundation makes the building buoyant, requiring use of a heavier, thicker slab, Indeed, if watertight closures had been in- stalled on a building at grade rather than the building raised three feet on fill, the cost would have been vir- tually prohibitive wilh a greater than 30 inch slab being required to counteract the buoyancy, As the building size and weight increase the structure eventually supplies sufficient dead load to counteract buoyancy without added depth and expense in the floor slab, Again, the relatively small size of the proposed commercial struc- ture becomes a critical factor in determining the most economical method of complying with National Flood Insurance Regulations,