Claudette Reichel | 7/10/2009 1:09:06 AM
Below are brief descriptions of currently available building systems referred to in the following Checklist. Some of the major properties that relate to criteria of sustainability are mentioned. At the end of the Reference Guide is a generalized assessment of how each building system integrates and balances the five criteria for Gulf Region conditions.
Standard Framing. Most homes in the region are wood framed with 2x4 lumber spaced 16 inches on center. Typical practices include using extra studs at corners to support wallboard, double top plates, uninsulated headers made from double 2x10 lumber over all windows and doors, and other traditional methods.
OVE/Advanced Framing. Optimum Value Engineering spaces and aligns floor, wall and roof framing at 24 inches on center (2-foot modules) and uses framing techniques that eliminate lumber not necessary for load-bearing purposes. Examples include two-stud corner framing, single top plates because of the aligned framing and insulated headers sized for the load-bearing need. (Figure 1, OVE Advanced Framing)
OVE reduces materials and labor. It also improves energy efficiency by displacing lumber with insulation, and it reduces construction waste. When using 2x6 lumber, advanced framing provides space for higher insulation levels (R-19 to R-21) and meets standard building codes (but some OVE framing techniques could be excluded by some locally established codes, in high wind zones, or if it’s unfamiliar to local building officials).
SIPS. Structural insulated panel systems combine structural framing and insulation into one product. They consist of rigid foam insulation sandwiched between two exterior structural panels, or skins, adhered to the foam. The skins are most commonly oriented strand board (OSB) panels, but they can be plywood, metal, a fiber-cement or other materials. SIPS are available in 4x8 feet and larger panels, up to 24 feet long and 4-12 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 to160 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 airtight construction that can result when using SIPS for both walls and the roof or ceiling. With precut panels, installation time can be less than half that of stick framing, with little construction waste. (Figure 2, Structural Insulated Panel Systems)
Masonry Construction. Masonry-wall homes (built with steel-reinforced concrete blocks or bricks, cast-in-place concrete or pre-cast tilt-up concrete panels) are uncommon in Louisiana but common in Florida and other hot, humid climate areas. “Brick homes” are usually wood frame with a brick veneer, so they are not actually masonry construction. Masonry walls are sometimes combined with wood or steel framing for some parts of the building, depending upon the cost and availability of skilled labor.
Masonry walls are typically insulated on the inside with rigid foam insulation and have a stucco exterior finish. Since this is a barrier and “reservoir” or water-storage building system, both the interior and exterior should be vapor permeable. Masonry is insect- and fire-resistant.
AAC. Autoclaved aerated concrete is a pre-cast concrete that has been chemically expanded (with gas bubbles) and steam cured under pressure in an autoclave to form building blocks or panels. This gives AAC an insulating value of about R-1.25 per inch, far more than that of regular concrete. It is lightweight, workable with common woodworking tools and insect- and fire-resistant. AAC can form an insulating, thermal mass benefit and low air infiltration without the addition of insulation material. (Figure 3, Autoclaved Aerated Concrete)
ICF. Insulating concrete form construction uses stacked blocks or panels of rigid insulating foam (or wood fiber composite) interlocked with internal connectors that are filled 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. (Figure 4, Insulating Concrete Forms)
Shotcrete Systems. Shotcrete is a process in which concrete is projected or "shot" under pressure using a feeder or "gun" 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 a variety of materials, including rigid foam insulation.
ISPS. An insulated sandwich panel system consists of prefabricated panels of rigid foam insulation sandwiched between two parallel sheets of galvanized steel wire mesh that are assembled and then sprayed with concrete on-site. Wire within the foam is typically welded to both sheets of wire mesh 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 insulating foam. (Figure 5, Insulated Sandwich Panel System)
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 specialized training and skills.
Steel framing contains some recycled material and its construction waste is 100% recyclable. It is lightweight, precise and highly resistant to warping and insects. Steel is fire-resistant but can twist or bend in a house fire. Since steel is a conductor of heat, “thermal bridging” greatly reduces the effectiveness of insulation within the wall cavity. It is much more effective and necessary 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.