Icf Insulated Concrete Form

Benefits: Above-Grade Walls

ICFs can be used in place of wood framing for most above-grade situations, placed on slabs or basement or crawlspace walls. Possible benefits of ICFs over wood framing include:

Strength, namely resistance to high winds

Energy efficiency / Comfort

Thermal Mass Noise abatement Durability
Reduced number of subcontractors and construction steps

Extension of the building season

Strength - Wind Resistance

The walls of a properly-constructed ICF home are exceptionally resistant to loads imposed by high winds. ICF walls will resist penetrating forces such as flying debris during high winds better than wood-framed walls, as shown in a PCA video.2 In both coastal hurricane areas and other high wind areas, where building codes require an analysis of wind resistance, typical ICF wall systems exceed current code requirements. It should be noted that in both conventional wood frame and ICF construction, the roof connection and construction and protection of windows are often most critical in avoiding wind damage, as are appropriate anchors to the footings and foundation.

Strength - Seismic Resistance

ICF structures can be designed for all seismic zones. The industry is only now starting to consider shear wall testing of ICF wall systems. Shear wall testing is needed to quantify the methods of compliance of ICF home designs in earthquake-prone areas.

Appearance

From the outside, ICF homes look similar to wood framed homes since a number of finishes such as EIFS and vinyl siding can be used. Homeowners may like the thick walls that provide deep interior window sills for use as window seats or window display areas, similar to the effect of adobe construction.

Energy Efficiency

ICF walls provide higher R-values (between R-18 and R-35)3 and lower air infiltration rates than typical wood frame construction (typically R-12 to R-20). However, wood frame construction
can be built to have comparable R-values and air infiltration rates for an additional cost that
would not likely exceed the cost premium typical of ICFs. ICFs also provide higher R-values than typical concrete or block foundation wall construction, perhaps with similar air infiltration rates. Concrete and block foundations can be insulated after construction to reach R-values equivalent to ICFs, but perhaps not as affordably and with some additional time and difficulty.

Thermographic testing by the NAHB Research Center, Inc. of an ICF home showed that a solid ICF wall (clear wall with no windows or penetrations) had fewer cold spots than a similar wood- framed wall. However, selection and installation of many other elements of a house, such as windows, ceiling insulation levels, air sealing methods, and HVAC equipment, all have an
impact on the overall energy efficiency of the house. The use of an airtight wall system such as ICFs does not automatically eliminate leakage through or around windows. Infiltration reduction is most effective with systematic air sealing of the entire house. Testing of leakage rates and

thermographic testing has revealed the importance of sealing air leakage paths in all components of the exterior envelope.

A recent study, Energy Comparisons of Concrete Homes versus Wood Frame Homes4 has quantified energy savings that are possible with ICFs. In this study, the energy use of 26 pairs of similar houses in the same climates were compared. An average energy savings of 44% (range:
36-53%) for space heating and 32% (range: 15-48%) for space cooling was found. Average
combined heating and cooling energy savings was 42% (range: 34-50%) and combined heating and cooling cost savings averaged 21% (range: 17-25%). Annual cost savings (based on actual local fuel costs) averaged $250 (range: $201 - 298). Projected savings for a 2,000 square foot house in Minneapolis was $376.

Percentage energy savings for ICFs compared to wood frame varied little by climate. (Based on the savings reported in this study, a rough simple payback analysis was conducted by Energy Design Update magazine and found to range from five years for an "optimistic" projection to 16 years for a more conservative, but not extreme, estimate). In the study, energy consumption was adjusted to account for differences in house size, design, foundation type, number of occupants, thermostat settings, and HVAC equipment. Construction specifications (insulation levels, air sealing techniques, etc.) were not provided for the framed houses.

When combined in a wall system with concrete, steel, and framing around openings, an R-value unique to the particular manufacturer’s wall system results. This R-value can be measured directly or can be calculated. Typical Clear Wall R-values range from R-13.5 to R- 22.5 for major manufacturers ICF products. Table 3 presents R-values of some typical materials used in wood frame and ICF construction.

 
 Table 3. TYPICAL R-VALUES OF MATERIALS   
Material, thickness R-value per inch of material R-value for given
Thickness   
EPS foam, 4 inches* 3.8-4.2 15.2   
XPS foam, 4 inches 5.0 20.0   
Polyisocyanurate foam, 4 inches ~7.0 ~28.0   
Fiberglass insulation, 3.5 inches 3.71 13.0   
Plywood, 1/2 inch 1.25 0.62   
Wood studs, 3.5 inches 1.23 4.30   
Double pane, vinyl window ("2826") NA 2.17   
Drywall, 1/2 inch 0.90 0.45   
Concrete, 8 inches 0.0625 0.50 
* varies with density

When considering reported R-values by manufacturers, it is important to understand how those values were determined and whether they are "thermal-mass adjusted R-value." This adjusted R- value is generally what most ICF manufacturers report. For most situations, thermal mass, especially when encased in foam, may not have any measurable effect on actual thermal

performance. The use of foam may in fact cause a negative effect on thermal lag, actually adding to peak and total HVAC loads.

Thermal Mass

Concrete has a high thermal mass--the ability to store heat and release it at a later time. In climates with large daily temperature swings, the mass effect of concrete walls can have a favorable impact on energy use and comfort. The presence of the foam can, however, decrease or eliminate the advantages of high thermal mass as the heat absorption and re-radiation is delayed (because of the thermal resistance of the foam) to the point that the mass effect is negated.

Noise Abatement

Research shows that for solid walls, ICFs are much better at reducing lower-frequency noise than wood frame walls. However, the addition of windows quickly diminishes the overall sound performance of a wall assembly. When combined with careful selection and installation of other building elements such as windows, doors, and roofs, ICF construction can provide excellent sound attenuation.

Durability

Foams and concrete hold the potential for improved building durability over wood construction because they are more resistant to moisture and less attractive to termites and other pests. Although foam is subject to moisture retention problems, ICF walls are more rot-resistant and durable than wood-framed walls.

Reduced Number of Construction Steps

With ICF construction, builders can use their framing crews to install a foundation which eliminates the need for a foundation contractor. ICFs also eliminate the need for additional wall insulation or an infiltration barrier.

Extension of the Building Season

Contractors can pour concrete in very cold conditions because the insulated forms keep heat in. Many builders reported that the limiting factor in pouring concrete for ICF construction was that you couldn't get a concrete truck to deliver at extreme temperatures.