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Lifting Concrete Floor Slabs Cuts Costs on Seniors Rehab

By Mark E. Dixon, Southwestern Editor

San Antonio, Texas -- Although usually used for new construction, lifting precast concrete slabs into place with jacks proved most cost-effective for conversion of a 76-year-old church into subsidized housing for the elderly.

The prospect Hill Baptist Church was transformed into the Prospect Hill Apartments for a total cost of $1.54 million, or about $49 per square foot, using Texstar Construction Corp.'s Lift Slab method.  The property has 55 units, all with rent subsidies under the Sec. 8 program, and 31,200 sq. ft. of floor space.

A registered historic landmark, the church was built in 1911 and suffered severe damage from fires in 1973 and 1980.  Rehabbing the building without altering the facade was the challenge for the developer, a joint venture between Ernest Breig and John Bratton and Liberty Homes of San Antonio.

Lifting the slabs into place did more than preserve the facades.  It made the project feasible, according to Breig.  "It was the difference between a project that was financially doable and one that wasn't," said Breig, who, with Bratton, operates an architectural firm in San Antonio.  Specifically, the Texstar system allowed the developers to do the following:

Slabs Poured Around Columns

In essence, workers first place the building's steel structural columns and then pour its basement floor.  Once that has set, the next floor is poured directly on top of the first.  The floors don't stick together because a curing and bondbreaking compound is applied between pourings.

At Prospect Hill, workers poured the basement floor and then pancaked four additional eight-inch slabs on top of it.  Hydraulic jacks on each of the 14 steel columns then lifted them into place a quarter inch at a time.  The roof went up first, then each of the three middle floors, from the top down.

"It took us about eight hours to lift the roof in place from the basement," recalled Breig.  "And when you think about it, that's a pretty good day's work."

To clear the walls, which were braced from the outside but still not perfectly straight, a five-inch gap was left around three of each slab's four sides.  On the fourth side, a three-foot gap was left -- the space required to "stress" the steel reinforcing rods inside each slab.

After each 136-ton slab was secured in place, these gaps were filled using conventional framing techniques.

The relative speed of this process saved more than $16,000 in interest charges during construction, according to Breig.

The technique also saved from $12,000 to $47,000 in hard construction costs, according to Ralph Geckler, president of Texstar Construction.  Geckler said his firm's price for pouring, lifting and securing the slabs was $5.15 per square foot.  Building with traditional framing could have cost anywhere from $5.50 to $6.50 per square foot at the time, Breig said.

The traditional way of pouring concrete floors in place is very labor intensive," he said.  "Basically, you're building a complete floor of wood, and then tearing it down."

Another $50,000 was saved because sprinklers were not required.  Concrete is considered a fireproof barrier, noted Breig.  Even steel is considered only fire resistant.

Finally, the eight-inch-thick slabs enabled Breig to get four floors of apartments into the 43-foot-high structure.  If he had built with wood, the combined flooring and support beams would have used 18 vertical inches per floor.  That's a total of six feet overall including the roof, as opposed to only 32 inches for the slabs.  Floors built of steel sheets and I-beams would have required 14 inches each, he said.

As it is, the ceilings in Breig's apartments are only eight feet high.  If the floors had been built of wood, the extra six feet would have required elimination of all of Prospect Hill's 15 fourth-floor apartments.

Also working in Breig's favor was the structure's listing on national and state historic registers.  At the time of its construction, it was the largest Baptist church in San Antonio.  That qualified the project for a 25 percent tax credit.

Multi-Housing News / May 1987

Mark E. Dixon