Increased emphasis on energy use in buildings has led many designers to believe that highly insulated walls are necessary for energy efficiency. While it is true that well designed walls can save energy and improve occupant comfort, high envelope insulation values do not translate into significant improvements in energy efficiency. Furthermore, such concerns as durability, maintainability, and long-term value, should be given their due in the selection process.
As wall insulation (R-Value) increases, the energy savings benefits level out. Beyond a relatively low insulation value in most climates, heating energy savings are outweighed by the extra costs of the insulation. This point varies, depending on building type and location, and on insulation cost.
Furthermore, although exterior walls play a significant, role in the overall energy performance of a building, they are but one of the elements in the building envelope. The mechanical, glazing and roof systems often have a greater impact of the energy used in the buildings.
In addition, recent studies of the thermal effect of mass exterior walls has shown that the location of the insulation in the exterior wall can have a significant impact. Interior insulation isolates the mass from the interior, reducing the ability of the thermal mass to moderate the indoor temperature. Integral insulation places thermal mass on both sides of the insulation, as does an insulated masonry cavity wall. This improves the thermal mass effect, reducing the energy used to heat and cool. Exterior insulation has the wall mass exposed to the interior, isolated from the exterior conditions by insulation. This last is the most thermally effective way to insulate the envelope of a thermal mass building.
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