New government programs are encouraging people to make their home more energy efficient and green. Insulation is an important part of an energy efficient home, but more is not always better. Adding it in previously uninsulated and under-insulated spaces can waste money and may damage your home. Understanding the potential problems will help you avoid costly mistakes.
When adding insulation, use the same type as the existing material. If this is not practical, then add new material that is similar in weight and density to the existing material. This is because heavier or denser material may compress the existing material. Compressed insulation does not have its full R value, so the combined R value could be less than the R value for each type. For example, installing loose fill cellulose over loose fill fiberglass will often compress the fiberglass because cellulose is heavier and denser than the fiberglass.
Adding insulation in attics, crawl spaces, and walls changes the conditions within those areas. For example, adding it to an attic should reduce the attic temperature in the winter because less heat from the home flows into the attic. Water vapor that moves from the home into the attic can condense into liquid water if the reduced attic temperature falls below the temperature at which water vapor condenses. Liquid water can damage the home and provide moisture for mold growth. This same problem can occur in crawl spaces and in wall cavities.
Take care not to cover any attic or crawl space ventilation openings when adding insulation. Covering ventilation openings may change the air flow and temperature in an area. These changes can allow water vapor to condense into liquid water.
Changes to air flow and temperature in the attic can contribute to ice dams. Ice dams form when snow melts on a roof over a warm attic. The water flows down to the cooler eaves where it freezes and forms ice. If this cycle of melting and freezing occurs, the liquid water can’t flow off the roof because of the ice dam. The water can flow under the roof covering and into the home.
Some batt insulation has a paper backing on one side. This is the vapor retarder. Do not install a vapor retarder over existing insulation. Moisture can collect on the vapor retarder and condense into damaging liquid water.
Some homes built during and before the 1930’s still have live knob and tube electrical wiring. This wiring consists of two insulated wires supported on porcelain spacers and uses porcelain tubes where the wires pass through wood. Do not cover these wires. Any covering can cause the wires to overheat and cause a fire.
Adding insulation in an attic can increase the weight on the home’s structural supports beyond the design capacity. This situation is unusual, but it can happen with older homes and when using heavier material such as loose fill cellulose.
More insulation is usually better for improving a home’s energy efficiency. If you are going to add it, take some wise precautions to understand the potential problems and to avoid unintended and damaging consequences.