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What is Insulation?

Updated on February 14, 2012

Why is insulation important?

Keeping heat inside your house during winter and outside it in summer is what insulation is all about.

Suppose your furnace is in good repair and your doors and windows are weatherstripped and tight. If on a chilly day you can still feel a miniature Niagara of cold air falling down the walls and cascading across the floor, your house may be poorly insulated-or not insulated at all.

How much energy will you save by installing insulation from scratch or beefing up your existing insulation? That depends on bany variables: the amount of insulation your house already has, your ceiling height, the number and size of windows, the presence or absence of storm doors and windows, the efficiency of your heating system, orientation of the house to the sun, and, of course, the we ther conditions where you live. The exact amount of mone you'll save also depends on the cost of fuel in your area.

You can save more than one-third of your house's total heat loss by insulating walls and roof. In most cases, fuel savings pay back the cost of insulating in less than 5 years. Because insulation is a permanent improvement, your energy savings will continue through the years you own the house. And when you sell, the insulation will increase the market value of your house.

Where insulation belongs

Insulation belongs inside any barrier between a heated space and an unheated one. Applied to the structure of a house, this means that insulation should be in all exterior walls, in attics, under floors exposed to the outside, and on heated basement walls.

Spots in which insulation is often overlooked include the wall between living space and an unheated utility room, storage room, or garage; dormer walls and ceilings; exterior walls between levels in a split-level home; knee walls next to heated attic rooms; overhead collar beams in a heated attic; and floors over vented crawl spaces, over unheated spaces, and cantilevered out over exterior walls.

Insulation should form a complete envelope around all living areas of your house, leaving no openings except doors, windows, and necessary venting. For further conservation, you should insulate around heating ducts and pipes.

A Priority List

Here are some factors to consider when deciding which areas to insulate first:


Particularly in a one-story house, most heat leaves through the attic. By installing sufficient attic insulation where there is none, you can cut up to 30 percent of your fuel bill. If your attic is unfinished, insulation is relatively easy to install; put this at the top of your priority list.

If you have a finished attic, insulate as much of it as you can. Flat roofs and mansard roofs present special access problems; talk to a contractor if you're considering insulation for one of these.


Exterior walls with no wall surface on one side are easy to insulate, and this should be a priority task. But most walls are covered on both sides, and for those you must either remove the wall covering on one side, then install rigid-board insulation over it and recover, or hire a professional to blow in or foam in insulation through scores of holes drilled for access. Removing the wall coverings would be absurd unless you plan to remodel the house.

As for hiring a contractor to insulate finished walls, you'll have to weigh the savings against the cost. Tests done by the Energy Research and Development Agency show that blowing in insulation doesn't do a complete job, and foaming in insulation is often too expensive to pay for itself in a reasonable period. But get a few estimates to find out the exact cost. By insulating walls properly, you can save 16 to 20 percent of your heating costs.

Basement or Crawl Space

If reasonably accessible, this is a good area to insulate. Doing so can save 5 to 15 percent of your heating costs. It is generally easy to insulate under floors that have an unfinished basement or crawl space below.

If your basement is heated and its walls are concrete, insulating involves some carpentry work. To install batts or blankets, you must build out each concrete wall with wooden framing members to provide room for them. Rigid-board insulation is attached to wood nailing strips bolted to the wall. After installing insulation, you cover it with gypsum wallboard or another approved wall covering.

In deciding whether or not to insulate a concrete basement wall, you must again weigh your projected savings against the cost and work of doing the job. If you plan to finish the basement anyway, insulating would be a wise investment.

Pipes, Ducts and Water Heater

Insulating these is an easy, low-cost job that returns sizable energy savings.


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