A first-cost comparison study released over a year ago by the Fire Safe Construction Advisory Council (FSCAC) concluded that compartmentalized concrete
A first-cost comparison study released over a year ago by the Fire Safe Construction Advisory Council (FSCAC) concluded that compartmentalized concrete construction is competitive with alternative methods that typically combine combustible materials and active fire suppression. Measured against wood- and steel-frame structures of identical configuration, FSCAC results indicated, additional costs incurred for the use of noncombustible concrete building materials were minimal, ranging from -3 to +5 percent. Moreover, the report maintained, long-term benefits of concrete construction, such as resistance to fire, mold, and water damage, can more than compensate for any first-cost premium. Possibly eliminating that negligible cost differential entirely, concrete industry professionals contend, are substantial savings due to longer spans and tighter construction schedules that precast affords.
Now, highlighting further economies offered by compartmentalized construction incorporating concrete-based methods is a follow-up study that compares energy use among the five building types in several Mid-Atlantic locations. To reflect the diversity of the multifamily dwelling marketplace, the studies’ residential building design consists of four stories; 25,000 sq.-ft. per floor; and, two interior layouts, including a one-bedroom and a mixed-bedroom plan. The five, fire-resistant construction types meet 2003 International Building Code (IBC) requirements, and building envelopes conform to the 2006 edition of the International Energy Conservation Code (IECC 2006), as follows:
- Conventional wood framing with a wood floor system using Type 5A or 5B construction;
- Light-gauge steel framing with a cast-in-place concrete floor system on a metal form deck;
- Load-bearing concrete masonry construction with a precast plank or a cast-in-place concrete floor system;
- Precast walls with a precast floor system;
- Insulated concrete form (ICF) walls or interior load-bearing CMU walls with a precast plank or a cast-in-place concrete floor system.
In Harrisburg, Pa., and Towson, Md., among other Mid-Atlantic sites, CTL Group performed a whole-building, hourly energy simulation to estimate annual energy consumption and operating expense. Energy costs for each city were derived from averages of the utilities serving the respective states. Each unit was equipped with a residential heating, ventilation and air conditioning system. In documenting the simulation, the report includes input parameters and results for the five building types.
In all cities, for both single- and mixed-bedroom schemes, ICF structures used the least amount of electricity and cost less to operate, the study finds. The next most energy-efficient building reportedly is the precast structure. Compared to the wood-framed building, ICF construction can save $2,800 to $7,300 annually in energy costs, depending on location and building type. The precast building can save $2,400 to $5,800 per year, the report concludes, compared to wood-framed structures of like configuration.
A glaring result of the study is the sizable impact on total energy consumption of equipment power density, i.e., plug loads comprising all electricity used for equipment and lighting. Plug or receptacle loads account for half the energy used in the residential units; thus, energy-efficient precast framing must be combined with conservative energy consumption to realize maximum savings. Accordingly, compartmentalized concrete construction constitutes an invaluable first step.
PRECAST VS. WOOD, STEEl
| Location | Exterior Wall Type (mixed BR) | Energy Use kWh | Electricity Cost with Plug Loads | Electricity Cost w/o Plug Loads | Cost Savings vs. Wood | Cost Savings w/ Plug Loads | Cost Savings w/o Plug Loads |
|---|---|---|---|---|---|---|---|
| Harrisburg, PA (Zone 5) | Precast | 568,300 | $59,300 | $30,694 | $2,800 | 5% | 9% |
| Harrisburg, PA (Zone 5) | Steel | 589,400 | $61,500 | $32,896 | $800 | 1% | 3% |
| Harrisburg, PA (Zone 5) | Wood | 597,700 | $62,400 | $33,763 | $0 | 0 | 0 |
| Towson, MD (Zone 4) | Precast | 578,600 | $56,300 | $29,608 | $2,500 | 5% | 9% |
| Towson, MD (Zone 4) | Steel | 625,300 | $60,800 | $34,152 | ($1,800) | -3% | -5% |
| Towson, MD (Zone 4) | Wood | 608,300 | $59,200 | $32,498 | $0 | 0 | 0 |
| Chart: Mid-Atlantic Precast Association | |||||||