MINIMUM CODE-MANDATED R-VALUE IN DIFFERENT CLIMATE ZONES
CITY
ZONE
WOOD FRAME
MASS WALL WITH MORE THAN HALF THE INSULATION ON THE OUTSIDE.
MASS WALL WITH MORE THAN HALF THE INSULATION ON THE INSIDE.
Burlington, VT
6
R-20
R-19
Louisville, KY
4
R-13
R-5
R-10
Las Vegas, NV
3
R-13
R-5
R-8
Miami, FL
1
R-13
R-3
R-4
Because of the thermal mass effect, the International Energy Conservation Code allows lower R-values for insulated concrete walls than for wood-framed walls. However as the table shows, the code recognizes that the thermal mass effect varies by climate and, to a lesser extent, by insulation placement.
Source:
http://energycode.pnl.gov/EnergyCodeReqs
Most window manufacturers have developed specialized products for ICF construction. As with any type of structure, careful sealing against air infiltration allows the mass of the walls an optimal performance.
In fact, ICF manufacturers point to the fact that the International Energy Conservation Code (IECC) specifies a lower minimum wall R-value for high-mass systems like insulated concrete.
But the thermal mass benefit of an insulated concrete wall--and the R-value discount offered by the IECC--will depend on exactly where the wall is built. The IECC recognizes 8 U.S. climate zones, with zone 1 being the warmest and zone 8 the coldest. As shown in Table 2, R-value discounts vary by zone, from a low of 1 to a high of 10.
In addition, not all hot climates are created equal. During the day, the mass of a concrete wall will soak up heat that otherwise would have gotten into the home; at night, when temperatures drop, any heat remaining in the wall will move back outside. The theory is that this process works best where there are very hot days and very cool nights, as in the Southwest desert.
Greg Kallio, a professor of mechanical engineering at California State University in Chico who specializes in heat transfer, recently tested this theory by modeling “the whole gamut” of wall systems, from stick-built to SIPs to insulated concrete, using industry standard energy analysis programs like EnergyPlus, as well as his own custom software. His conclusion? “The effectiveness of thermal mass is very dependent on diurnal temperature variation. You want nighttime temperatures that get at least 10 degrees cooler than the thermostat set point. If you keep the thermostat at 78, outside temperatures need to fall below 70 degrees at night to really take advantage of the thermal mass.”
While manufacturers don’t claim that thermal mass works as well Minneapolis as it does in Phoenix, they insist that it’s still an asset during cold northern winters. Nesset says this has been documented by computer simulations done at Oak Ridge National Laboratory. “A mass wall might be 3 times more effective in Phoenix than the baseline you would expect from the insulation alone, but in Minneapolis it will still be1.5 times more effective than the baseline.
10.2011
19
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68