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Insulation, like ventilation, is often a source of problems that span a spectrum depending on whether too little or too much insulation is present in the walls and ceiling of a home. Too much insulation, inexpertly stuffed in walls and ceilings can reduce the R-value just as the presence of too little can. Insulation that is not properly backed with vapour barrier can be a breading-ground for mold and mildew. Typically every Home Inspection includes a detailed assessment of the overall insulation quality of a home. The effectiveness of an insulation material’s resistance to heat flow also depends on how and where the insulation is installed. For example, insulation that is compressed will not provide its full rated R-value. Fiberglass insulation should never be installed sideways as this affects the heat conduction negatively.
How Insulation Works
To understand how insulation works it helps to understand heat flow, which involves three basic mechanisms — conduction, convection, and radiation. Conduction is the way heat moves through materials, such as when a spoon placed in a hot cup of coffee conducts heat through its handle to your hand. Convection is the way heat circulates through liquids and gases, and is why lighter, warmer air rises, and cooler, denser air sinks in your home. Radiant heat travels in a straight line and heats anything solid in its path that absorbs its energy.
Most common insulation materials work by slowing conductive heat flow and–to a lesser extent–convective heat flow. Radiant barriers and reflective insulation systems work by reducing radiant heat gain. To be effective, the reflective surface must face an air space.
Regardless of the mechanism, heat flows from warmer to cooler until there is no longer a temperature difference. In your home, this means that in winter, heat flows directly from all heated living spaces to adjacent unheated attics, garages, basements, and even to the outdoors. Heat flow can also move indirectly through interior ceilings, walls, and floors–wherever there is a difference in temperature. During the cooling season, heat flows from the outdoors to the interior of a house.
To maintain comfort, the heat lost in the winter must be replaced by your heating system and the heat gained in the summer must be removed by your cooling system. Properly insulating your home will decrease this heat flow by providing an effective resistance to the flow of heat.
A recent study in California where 30 homes were inspected to determine the quality of workmanship used when installing fiberglass batts found every one of the 30 homes had poorly installed insulation. Fiberglass batts have to be cut to fit properly and when there is custom roofing framing involved poor fitting insulation seems to be the norm.