Insulation: The Facts Part 1

The Old House Web

Topicscovered in Part 1: The role ofinsulation * Insulation priorities * What isR-value?

insulationItmakes good sense to turn lights and appliances off when they are not needed, butyou'll save even more on your energy costs if your reduce the amount of energy needed for heating andcooling.

Heating and cooling ("space conditioning") account for 50 to 70% ofthe energy used in the average American home. About 20% goes for heating water.On the other hand, lighting and appliances and everything else account for only10 to 30% of the energy used in most residences.

Unless your home was constructed with special attention to energy efficiency,adding insulation will probably reduce your utility bills. Much of the existinghousing stock in the United States is not insulated to the best level.

Olderhomes are likely to use more energy than newer homes, leading to very highheating and air-conditioning bills. Even if you own a new home, addinginsulation may save enough money in reduced utility bills to pay for itselfwithin a few years, continue to save you money for as long as you own the home,and increase the resale value of your house.

The crucial role of thermal insulation

Inadequate insulation and air leakage are leading causes of energy waste inmost homes. Insulation saves money and our nation's limited energy resources. Itcan also make your house more comfortable by helping to maintain a uniformtemperature throughout the house. Walls, ceilings, and floors will be warmer inthe winter and cooler in the summer. Insulation can also act as a sound absorberor barrier, keeping noise levels down.

It is possible to add insulation to almost any house. You may be able to dothe job yourself if the structural framing is accessible--for instance, inunfinished attics or under the floor over an unheated space. Or, you may preferto hire an insulation contractor. In either case, it is important to choose andinstall the insulation correctly.

The amount of energy you conserve will depend on several factors: your localclimate; the size, shape, and construction of your house; the living habits ofyour family; the type and efficiency of the heating and cooling systems; and thefuel you use. Once the energy savings have paid for the installation cost,energy conserved is money saved--and the annual savings will increase if utilityrates go up.

Insulation priorities

It is most important to:

  • Insulate your attic to the recommended level, including the attic door, or hatch cover.
  • Provide the recommended level of insulation under floors above unheated spaces, around walls in a heated basement or unventilated crawl space, and on the edges of slabs-on-grade.
  • Use the recommended levels of insulation for exterior walls for new house construction. When remodeling or re-siding your house, consider using the levels recommended for new construction in your existing walls.

What is R-value?

Heat flows naturally from a warmer to a cooler space. In the winter, thisheat flow moves directly from all heated living spaces to adjacent unheatedattics, garages, and basements, or to the outdoors; or indirectly throughinterior ceilings, walls, and floors--wherever there is a difference intemperature.

During the cooling season, heat flows from outdoors to the houseinterior. To maintain comfort, the heat lost in winter must be replaced by yourheating system and the heat gained in summer must be removed by your airconditioner. Insulating ceilings, walls, and floors decreases this heat flow byproviding an effective resistance to the flow of heat.

Insulation is rated in terms of thermal resistance, called R-value, whichindicates the resistance to heat flow. The higher the R-value, the greaterthe insulating effectiveness. The R-value of thermal insulation depends onthe type of material, its thickness, and density. In calculating the R-value ofa multi-layered installation, the R-values of the individual layers are added.Installing more insulation in your home increases R-value and the resistance toheat flow.

The effectiveness of an insulated wall or ceiling also depends on how andwhere the insulation is installed.

For example, insulation which is compressed will not give you its full rated R-value. Also, the overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself because some heat flows around the insulation through the studs and joists. That is, the overall R-value of a wall with insulation between wood studs is less than the R-value of the insulation itself because the wood provides a thermal short-circuit around the insulation.

The short-circuiting through metal framing is much greater than that through wood-framed walls; sometimes the metal wall's overall R-value can be as low as half the insulation's R-value. With careful design, this short-circuiting can be reduced.

To Part 2: Does your home need more insulation ->

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