Structural Insulating Panels (SIP): Structural insulating panels (SIP) often consists of a foam board core sheathed on one or both sides with plywood, oriented strand board (OSB) or gypsum board (drywall.) The insulation is usually polystyrene or isocyanurate, but foam-straw composites are sometimes used too. Panels range in size, but are most common in 4 x 8 foot to 4 x 10 foot (1.2 x 2.4 meter to 1.2 x 3.04 meter).

Because of their structural strength, SIPs reduce the need for structural lumber, opportunities for air leaks, and installation errors common with stud frame (stick-built) construction. It is also faster to build SIP wall assembles than many other construction methods. Most comparison studies between stick-built and SIP house show significant energy saving with the SIPs. Because these panels also reduce sound transmission, some designers use them for interior partitions too.

SIP roof panels sometimes have a nailable layer only on one side. It's purpose is as a retrofit over an existing roof where additional insulation is desired but no attic exists under the roof deck. The insulated roof panels are also available with air channels just under the exterior sheathing for ventilated roof designs.

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Figure 63: Structural Insulating Panels

Insulating Concrete Forms (ICF): An ICF system consists of interlocking foam board and occasionally hollow-core foam blocks. The foam board forms are held vertical and parallel to each other by plastic or steel rods and ties. After adding the appropriate reinforcing steel rods (rebar) and poured concrete, the result is a very strong and insulated concrete wall. Such a building can be made from foundation to roofline. Some innovative builders make the roof of ICF as well.

Because of its flammability, any ICF exposed to the occupied space must be covered with an appropriate fire-resistant material. Most codes find half-inch (12.7mm) drywall acceptable. The exterior of the building can be finished with anything the designer finds desirable.

Other systems use the rigid insulation board in the center of the concrete wall. These are often referred to as "tilt-wall" construction. The walls are poured in a form on a flat deck and after curing are "tilted" upright into position by a crane. Because the insulation board is inside the wall it reduces problems relating to fire and insect infestation.

Insulation block systems are typically hollow core polystyrene blocks that interlock to create the ICF wall system. Steel reinforcing rods are often used inside the block cavities to strengthen the wall. One draw-back of stacked block ICFs is that the foam webbing around the concrete filled cores provides easy access for insects and ground water to enter the building. To minimize these problems, some manufacturers make insecticide treated forms and often promote a water proofing method for the foam blocks.

Concrete Block Insulation: Insulated concrete blocks take on many different shapes and compositions. The better concrete masonry units reduce the area of connecting webs as much as possible. The cores are filled with insulation-poured-in, blown-in, or foamed-in-except for those cells requiring structural steel reinforcing and concrete infill. This raises the average wall R-value.

Some block makers coat polystyrene beads with a thin film of concrete. The concrete serves to bond the polystyrene while providing limited structural integrity. Expanded polystyrene mixed with Portland cement, sand, and chemical additives are the most common group of ingredients. These make surface bonded wall assemblies with a wall R-value of R-1 per inch thickness. Polystyrene inserts placed in the block cores increase the unit thermal resistance to about R-2 per inch.

Hollow-core units made with a mix of concrete and wood chips are also available. They are installed by stacking the units without using mortar (dry-stacking). Structural stability comes from the concrete fill and appropriate rebar throughout for structural walls. One detracting point of this type is that the wood component is subject to the effects of moisture and insects.

Two varieties of solid, precast autoclaved concrete masonry units are now available in the U.S.: autoclaved aerated concrete (AAC), and autoclaved cellular concrete (ACC). This class of material has been commonly used in European construction since the late 1940s. Air makes up 80% (by volume) of the material. It has ten times the insulating value of conventional concrete. The R-1.1 per inch blocks are large, light, and have a flat surface that looks like a hard, fine sponge. Mastic or a thin mortar is used to construct a wall. The wall then often gets a layer of stucco as the finish. Autoclaved concrete is easily sawn, nailed, and shaped with ordinary tools. Since the material absorbs water readily, it requires protection from moisture.

Precast autoclaved cellular concrete uses fly ash instead of high-silica sand as its distinguishing component. Fly ash is a waste ash produced from burning coal in electric power plants. The fly ash is the material that differentiates ACC from AAC.

Specialized Devices: A wide variety of rigid insulation inserts are available to fill many critical locations in the insulated envelope of houses. Some examples are to use inserts as air chutes, insulation dams, concrete block fillers, and ice dam retarders. Expanding foams efficiently seal and weatherize homes. Devices as simple as cardboard can be used to provide an insulation dam to help keep loose-fill insulating material around attic ductwork.

Natural Fibers: Several natural fibers are being analyzed for their potential insulating properties. The most notable of these include cotton, wool, hemp, and straw.

Cotton thermal insulation is no longer produced in the United States, however you may still be able to find small quantities in some areas. Cotton based insulation consists of recycled cotton and plastic fibers that have been treated with the same flame retardant and insect/rodent repellent as cellulose insulation. It meets the same Class I standards for fire resistance as fiberglass insulation. Cotton insulation has similar thermal properties as fiberglass and cellulose insulation (R-3 or so per inch of thickness.) Some chemically sensitive consumers feel that this type of insulation is "healthier" to use than other types. However, field studies have proven that this is generally not the case, and other sources of indoor air pollution are of more concern than the type of insulation.

Wool and hemp insulation are relatively unknown in the U.S., but have been in use in other, less industrialized countries. Both products offer similar R-values to other fibrous insulation types (about R-3.5 per inch of thickness.)

Straw bale construction, popular 150 years ago on the Great Plains of the United States, is receiving renewed interest. Straw bales tested by the Oak Ridge National Laboratory yielded R-values of R-2.4 to R-3.0 per inch. But at least one straw bale expert claims R-2.4 per inch is more representative of typical straw bale construction due to the many gaps between the stacked bales.

Straw Panels: The process of fusing straw into boards without adhesives was developed in the 1930s. Panels are usually 2 to 4 inches (51-102 mm) thick and faced with heavyweight Kraft paper on each side. Although manufacturer's claims vary, R-values realistically range from about R-1.4 to R-2 per inch. They also make effective sound-absorbing panels for interior partitions. Some manufacturers have developed SIPs from multiple-layered, compressed-straw panels.

Many types of insulation products are rapidly becoming incorporated into conventional construction. They may provide a convenient or sometimes a healthier approach to increasing the energy efficiency of a building. However, it is important to note that because some materials have been on the market for only a short time they may not be widely available and performance and durability of some materials may not be well documented. Always carefully research material characteristics for suitability for your purposes.

Figure 64: Conversion Factors for English (Imperial) R-values to metric International System units (SI.)

R-Value Conversions

To get



Thermal Resistance (R)

RSI (m2 C/W)

R (ft2h° F/Btu)


Insulation R/unit thickness




Note: The standard unit of measurement in the United States has been the Imperial unit. To differentiate it from the metric system the term 'SI is used. For example, RSI refers to the R-value in International System (SI) or metric units.

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