Thermal insulation is defined as the reduction of heat transfer or as a method of preventing heat from escaping or entering an object. It helps in maintaining a certain temperature in a particular area.
Thermal insulation seeks to reduce the heat flow between two objects or areas of different temperatures. The property of a material to withstand heat flow is known as thermal resistivity (r). This is a reciprocal of thermal conductivity (k or which is the property of the material to conduct heat.
Measurement: Thermal resistivity is measured in m.K/W in SI units and multiplying this with the thickness of the material gives us the thermal resistance R in m2.K/W. Adding all the thermal resistances for a particular barrier i.e. wall, roof or floor and taking its reciprocal gives us the U value known as thermal transmittance.
Energy Terms
Energy terms are often confusing and sometimes not suited to the situation in which they are used.
Terms like “tested R-value,” “performance R-value”, and “K-value” need to be better understood in order to appreciate the advantages of Polystyrene. In the past there has been much speculation about the high R-values –often 50% or greater compared to conventional construction. A short review is then in order for the basic course in energy conservation.
Convection is the transfer of heat by the motion within a fluid or gas—like central air heating. Convection is the largest form of heat loss from a structure and can be addressed by airtight construction methods like ICF, which limit the amount of air that can get through the building envelope. “Tested R-values,” however, don’t consider the level of airflow through the wall, which is one reason why many claim R-values don’t accurately represent the insulating properties of an R-22 wall.
Incidentally, convection is also the most efficient way to heat a structure. Warm air rises off a heated floor; cool air falls to the floor to be warmed.
Conduction is the transmission of heat across matter. If you’ve ever burned yourself on the handle of a cast iron skillet, you probably know conduction is the strongest form of energy transfer and the most constant. An un-insulated concrete floor is constantly losing heat to the environment 24 hours a day through conduction, which is why some builders install an under slab thermal barrier.
While convection is the largest form of heat loss, walls, floors and ceilings will also conduct heat to and from the environment unless the conductivity, or K-value, of the materials is very low. K-value, represented in physics by the letter lamda, is the ability of a material to conduct heat. In order to build energy efficient structures, materials of a low thermal conductivity are desirable both above and below grade. The lower the K-value, the better the material is for insulation.
Expanded Polystyrene (EPS), which is used to make insulating concrete forms, has a K-value of 0.033. For comparison, fiberglass insulation has a K-value ten times higher (0.33), while wood has a K-Value of 0.76, and marble has a K-Value of 11.0.
Radiation: Convection is the transfer of heat by the motion within a fluid or gas—like central air heating. Convection is the largest form of heat loss from a structure and can be addressed by airtight construction methods Like Polystyrene, which limit the amount of air that can get through the building envelope.
Thermal Mass: Another consideration in calculating energy efficiency is the thermal mass of the structure. A thermal mass in the most general term refers to anything used to absorb and hold heat. Dense materials like stone, concrete, adobe or water work best. Since Polystyrene couples non-conductive foam with an energy-holding thermal mass, any energy that may bridge the polystyrene is absorbed and held by the concrete –perfect redundancy for the energy envelope.
Finally, the term U-Value is the total amount of energy transfer through convection, radiation and conduction. This is an architectural term used to describe the energy efficiency of a structure, calculated using a formula that considers the materials specified for the building envelope—floors, walls and ceilings.
Energy efficient structures keep warm air in, radiant energy out and do not conduct energy in or out of the energy envelope.
In summary, the R-Value is a number that has been poorly defined and is even more poorly understood in terms of performance. A structure with R-22 walls, SIP (structurally insulated panel) roof, and a foam insulated floor will outperform any other type of conventional structure with double the R-Value (R-40+) in energy efficiency, structural strength and return on investment in most any type of side-by-side comparison. Why? Because polystyrene is airtight, non-conductive, have good thermal mass.
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R-Value of the EPS will reduce conduction by about half.
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Thermal mass of the concrete will smooth out large swings in temperature.
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Air infiltration (convection loss) is reduced to near zero, saving 30% or more on heating/cooling costs.
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