Thermal Energy Efficiency
Performance Statement: Houses built with Pinkform XtraTM exterior walls use 9% less energy(nationally averaged) in heating and cooling versus typical wood-framed construction. The energy savings are due to increased insulation (7%) and thermal mass of concrete (2%). These savings are based upon currently accepted thermal modeling techniques. Additional energy savings, over the 9% mentioned above, are to be expected due to reduced air infiltration (see Air Infiltration Statement). Energy studies of 27 existing homes built with this type of exterior wall (called ICF for short) concluded that ICF homes require an estimated 44% less energy to heat and 32% less energy to cool than comparable wood-framed homes. Work is underway to understand the differences between this study and accepted thermal modeling techniques.
What Does This Mean For You? Using Pinkform XtraTM exterior walls in your home may provide significant monthly savings in your heating and cooling bills. Some mortgage companies recognize that lower heating and cooling costs for the homeowner represent lower risk to them; therefore, you may experience a reduction in mortgage costs such as lower points up front, a lower interest rate, or an ability to borrow more money relative to your income. In addition, lower energy requirements may result in a downsizing of the HVAC cooling system for your home which means more upfront savings for you.
Explanation: Energy performance of walls is dependent upon many things; but, three of the most important factors are:
Thermal resistance is the resistance to heat flow through materials. Air infiltration is the movement of air through "air leaks" in the wall. Thermal mass is a material's ability to absorb and release heat. Thermal mass reduces interior temperature swings due to changes in exterior temperatures; thus, helping to warm the house during cool evenings and cool the house on warm summer days.
The measure for thermal resistance is R-value. The greater the R-value, the better the thermal performance. A typical wood-framed wall has an R-value of 14.4; whereas, the typical R-value benefit of a Pinkform XtraTM wall is 25.3 as the following chart illustrates (on average, thermal mass of 4" of concrete provides an energy savings equivalent to insulation with an R-value of 3.6):
Thermal Performance
Wood-framed Pinkform XtraTM
FG Insulation 13.0 20.0 Foam Insulation
Sheathing Ins 3.5 0.4 Concrete(4 inches)
Other* 1.3 3.6 Thermal Mass(concrete)**
Framing Adjustm't -3.4 1.3 Other*
R-value 14.4 25.3 Overall R-value Benefit
*Other: inside air film, 1/2" gypsum wallboard, outside air film
**Calculated national average R-value benefit
Source: Owens Corning Unpublished Calculations
The difference in thermal performance of the above walls accounts for the average 9% energy savings nationwide. Approximately 1/4 of the 9% savings results from the thermal mass properties of concrete. Locations with high day-to-night external temperature variations above and below the internal temperature of a home will experience greater energy savings due to thermal mass. Estimated energy savings due to Pinkform XtraTM for 233 locations in the U.S. are listed in Exhibit 1.
Energy savings tend to increase with the size of the home and type of climate (greater heating savings in colder climates; greater cooling savings in warmer climates).
In addition, due to the reduced energy usage, HVAC cooling equipment can be downsized as a result of using ICF construction for external walls.
Sources:
VanderWerf, Energy Consumptions Comparisons of Concrete Homes vs Wood-framed Homes. PCA. 1997
Van Geem, Guidelines For Using The CABO Model Energy Code With Insulated Concrete Forms. PCA. 10/97
Van Geem, Guidelines For Using ASHRAE 90.2-1993 With Insulated Concrete Forms. PCA. 10/97
PCA, "Residential Technology Brief-Concrete Homes Save Energy", No.1, IS300
Wilcox, Technical Analysis for Using Energy Codes for ICF Homes. PCA. 10/97
Owens Corning Unpublished Calculations, 6/98
Van Geem, Gajda, Wilcox, Sizing Air Conditioning and Heating Equipment for Residential Buildings with ICF Walls. PCA. 1998
Air Infiltration
Performance Statement: A house built with Pinkform XtraTM exterior walls can have up to 67% less air infiltration than a typical wood-framed home.
What Does This Mean For You? Less air infiltration in your home means a "tighter" home with less air leakage and fewer drafts. That means, a "tighter" home requires substantially less energy to heat and cool. In addition, a "tighter" home minimizes temperature differences between the floor and ceiling, room to room, and floor to floor-making temperatures more consistent and your home more comfortable, all year round.
Explanation: Air infiltration is measured in air changes per hour(ACH) determined by blower door tests. Wood-framed homes have numerous paths of air leakage due to their component construction. Drafts usually develop around interfaces between components such as electrical boxes, band joists, sheathing joints, etc. In fact, up to 33% of the energy loss in a typical wood-framed home is attributed to air infiltration as the below chart illustrates:
Source: PCA, "Residential Technology Brief-Concrete Homes Save Energy", No.1, IS300
Depending on how a wood-framed home is constructed, ACH ratings vary between 0.3 to 0.7 (ASHRAE 1993) with a typical home being 0.5. In comparison, Pinkform XtraTM construction eliminates many air infiltration sources due to its monolithic nature resulting in reduced ACH ratings of .12 to .35 ACH with a typical home being .17 ACH.
Note: It is recommended that any home with less than .35 ACH have mechanical ventilation such as, an air exchanger or air-to-air heat exchanger, to maintain satisfactory levels of indoor air quality.
Sources:
National Association of Home Builders Research Center, Insulating Concrete Forms For Residential Construction, U.S. Dept. Of Housing & Urban Development
VanderWerf, Feige, Chammas, and Lemay, Insulated Concrete Forms for Residential Design and Construction. McGraw Hill. 1997
PCA, "Residential Technology Brief-Concrete Homes Save Energy", No.1, IS300