Residential rebuilding in post-Katrina New Orleans has increased our awareness of various ways to frame a house. Here are brief descriptions of currently available exterior building systems.
- Standard Wood Framing: Most home in Louisiana are wood framed with 2-by-4 lumber spaced 16 inches on center. Typical practices include using extra studs at corners to support wall-board and double top plates and uninsulated headers made from double 2-by-10 lumber over all windows and doors.
- Optimum Value Engineering (OVE) Wood Framing spaces and aligns floor, wall, and roof framing at 24 inches on center (2-foot modules) and uses framing techniques that eliminate lumber that isn’t necessary for load-bearing purposes. Examples include two-stud corner framing, single-top plates because of aligned framing and insulated headers sized for the load-bearing need. OVE reduces materials and labor. It also improves energy efficiency by displacing lumber with insulation, and it reduces construction waste. When using 2-by-6 lumber, advanced framing provides space for higher insulation levels (R-18 to R-21) and meets standard building codes. Some OVE framing techniques, however, could be excluded by local codes in high wind zones, or if it’s unfamiliar to local building officials.
- Structural Insulated Panel Systems, or SIPS, combine structural framing and insulation into one product. It consists of rigid foam insulation sandwiched between two exterior structural panels, or skins, adhered to the foam. The skins are most commonly oriented strand board panels, but they can be made of plywood, metal, a fiber cement, or other materials. SIPS are available in 4-by-8 feet or larger panels, up to 24 feet long and 4 to 12 inches thick. They can be cut on site, but are usually ordered from the factory as a package, ready to assemble with all window and door openings precut and channels through the foam core for wiring. SIPS have high-strength characteristics and can be designed to withstand winds up to 160 mph. They have excellent energy-efficiency performance because of the nearly uninterrupted R-15 (4.5 inch panel) to R-48 (12.25 inch panel) insulation and air-tight construction that results from using SIPS for both walls and roof or ceiling. With percent panels, installation time can be less than half that of wood framing, with little construction waste.
- Insulating Concrete Form, or ICF construction uses stacked blocks or panels of rigid insulating foam (or wood fiber composite) interlocked with internal connectors that are filled on site with poured concrete and steel rebar to create structural walls. The foam forms and plastic connectors stay in place as a permanent part of the wall assembly. This provides a continuous insulation and sound barrier, as well as a backing for drywall on the inside, and stucco, lap siding or brick on the outside. Typical insulation values of ICF walls are much higher than other masonry systems (R-17 to R-26, depending on material and thickness). Energy performance also benefits from the thermal mass and low air infiltration. ICF walls can be designed for high wind resistance and are highly resistant to water damage and decay, even from long-term flooding or wetness.
- Shotcrete Systems: Shotcrete is a process that uses a pressurized feeder or “gun” to “shoot” concrete onto a surface to form structural walls, floors, and roofs. The system offers design flexibility in forming shapes and can create finishes of various textures and colors without additional exterior cladding or interior drywall. The core surface can be made from a variety of materials, including rigid foam insulation.
- Insulated Sandwich Panel Systems, or ISPS, consist of prefabricated panels of rigid foam insulation sandwiched between two parallel sheets of galvanized steel wire mesh that are assembled, then sprayed with concrete on site. Wire within the foam is typically welded to both mesh sheets to create a strong, truss-like support system. Plumbing and wiring are run through cut or pre-formed channels in the foam core. Window and door openings are cut before the panels are coated with sprayed concrete (shotcreted) on both sides. Panels have R-values from 7 to 33, depending on thickness of the insulation foam.
- Steel Framing: Residential steel framing is made from sheet steel that is roll-formed into shapes used for framing (usually C shape) and galvanized to resist corrosion. It is laid out similar to wood framing, but the fastening process is different. A steel-framing crew needs some specialized training. Steel framing contains some recycled material and its construction waste is 100 percent recyclable. It is lightweight, precise and highly resistant to warping the insects. Steel is fire resistant, but can twist or bend in a house fire. Since steel is a conductor of heat, that “thermal bridging” greatly reduces the effectiveness of insulation within the wall cavity. It is much more effective to use rigid insulation sheathing outside the studs. Steel is sensitive to moisture and can corrode or rust, especially in coastal areas and if flooded with salt water.