Thermal Resistance Of Roofing Materials

For instance if you have a material with an r value of 12 attached to another material with an r value of 3 then both materials combined have an r value of 15.

Thermal resistance of roofing materials. If just metal sheets are used on the roof they often come up against difficulties in guaranteeing good walkability resistance. For example a characteristic of a heat sink. Most roofing membranes have high thermal conductance whatever gets into the membrane gets out just as fast. Absolute thermal resistance r in kelvins per watt k w is a property of a particular component.

An rsi 3 52 r20 per 152 mm batt compressed into a 140 mm cavity has a thermal resistance value of 3 34 r19. It is common sense for insulating material to retain heat well and the r value is a measure of how good a product or material is at doing so. Thermal resistance is a heat property and a measurement of a temperature difference by which an object or material resists a heat flow thermal resistance is the reciprocal of thermal conductance. The third factor that affects the energy efficiency of the roofing system is the thermal conductance of the roofing materials.

Specific thermal resistance or thermal resistivity r. Hour degf. Thermal resistance is the reciprocal of thermal conductivity. Low thermal conductivity value of 0 038 0 041 w m k compressive strength in the range of 40 80 kpa which is sufficient for exposed roofing applications weight is in the range of 100 200 kg m 3.

R value has the units of m2k w. Building insulation of course is what we are normally referring to when we say thermal insulating materials but in a commercial roof system the r values of other components such as underlayment cover boards and even some adhesives can often be included when calculating the total r value of the system. K btu inch sq ft. C or thermal conductance of these materials is the reciprocal of the r value.

The thermal resistance of unit area of a material is measured by the r value. To counteract this thermal insulation has been a part of roofing systems for many years. The r value is proportional to the thickness of the products or material. As we said before the r value measures the thermal resistance of a material.

C is known only when the k the thermal conductivity of a material is known. K is the heat transmitted through a 1 inch thickness of homogenous material per square foot per hour when there is 1 degree of temperature change.