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 Correct insulation is a key element for a more comfortable and energy efficient home. It is important to have a continuous boundary of insulation between the conditioned, indoor spaces and the unconditioned, outdoor spaces.
This boundary is referred to as the "building envelope" and consists of the walls, floor, and ceiling or roof. Low insulation levels and gaps or voids in the insulation materials can provide paths through which heat and air can easily flow into or out of the residence. Care must be taken to shape the insulation material around piping and electrical work without compressing it. Building codes typically require a minimum insulation level for each component of the building envelope. These levels vary from state to state depending on climate conditions. In most climates, it is both easy and cost effective to increase these insulation levels beyond the minimum code requirements. Insulation materials available include batt-type, loose fill, rigid foam panels, and spray-type. Insulation materials are rated according to their ability to resist heat flow. This thermal resistance rating is commonly known as an "R-value". The higher the R-value of a material, the better its ability to resist heat flow. The reciprocal of the R-value is the U-value, which characterizes the rate of heat loss. If moist air gets inside the building envelope and condenses on cold surfaces, it can cause damage to the insulation and building structure. In cold climates it is recommended to keep the insulation and envelope cavities dry by applying a vapour retarder or low permeability paint to the warm side of the envelope. BENEFITS * Improved comfort. Increased insulation reduces conductive heat losses and gains resulting in warmer interior surfaces in the winter and cooler interior surfaces in the summer. Approximately 40 percent of our physical comfort in homes is due to radiant heat exchange between our bodies and the surrounding interior surfaces. Increased insulation reduces this radiant heat exchange and minimizes temperature differences between rooms, thus maintaining a more consistent level of comfort throughout a house. * Improved indoor air quality. When insulation levels are increased and materials properly installed, there are fewer gaps and voids through which unconditioned air can leak into a house. This helps avoid dirt, dust, and other impurities that can negatively affect indoor air quality. A tight building envelope is a critical component to ensure good indoor air quality. * Increased construction quality. Building codes establish the legal minimum construction standards. Energy Efficient Homes are constructed to significantly exceed these codes. Figure 2 shows that to increase insulation levels, builders must install an insulation material with a higher R-value or increase the thickness of the building envelope component. In either case, the result is better quality construction. This is particularly true in cases where special care is taken during installation to insure no gaps or voids are left in the insulation. * Reduced obsolescence. Based on recent trends for improved efficiency, building envelopes with increased insulation levels are expected to become industry practice. Since it is both difficult and costly to increase insulation after a house is built, it is best to increase insulation levels during the original construction. Energy efficient Homes constructed to exceed minimum building codes requirements are, therefore, expected to be less vulnerable to obsolescence. * Lower utility bills. More than 40 percent of the energy consumed in a typical household goes to heating and cooling. Increased insulation reduces this energy consumption which lower energy consumption results in lower utility bills. * Improved resale position. Increased insulation levels can provide the many impressive benefits listed above resulting in a more comfortable, higher quality home with better indoor air quality and lower utility bills. These benefits can translate into higher resale value. R-VALUES FOR VARIOUS INSULATION MATERIALS Insulation materials are often characterised by their R value. In countries like Australia, which use metric measures, the units of R are m²K/W. An R=2 insulation material passes 0.5 watts per square metre with a 1 degree temperature difference. In countries using imperial measure, R is based on imperial units and a 50mm rock wool batt would have an R of around 40. The air film against a surface has a significant effect and must be included in the calculation. For example when calculating the nett R of a weatherboard external wall the total R value is:
0.04 + 0.12 + 0.14 + + 0.077 + 0.14 = 0.517
0.04 + 0.27 + 0.14 = 0.45
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