How Does Insulation Work?

Warming up to domestic insulation

Heat always tries to move from a warmer place to a cooler one. That's why homes need air conditioning in the summer and furnaces in the winter. However, the energy produced by heaters or air conditioners can be wasted. That's where insulation comes in.

Home insulation slows the natural movement of heat, keeping your home cool when it's hot outside, and hot inside when it's frosty outdoors.

How heat moves

Heat transference is an expensive problem. About two-thirds of the average homes energy budget is spent on heating and cooling. Poor insulation and air leakage can needlessly increase energy costs and put greater demands on heating and cooling equipment.

There are three ways that heat moves from warm to cold spaces:

Radiation

Heat transferred through invisible electromagnetic light waves.

Conduction

Heat transferred through one object and into another.

Convection

Heat transferred into air or water through a material object.

The materials used in home insulation can drastically slow these three heat-transference processes.

Insulation materials

The efficiency of an insulation material is indicated by its R-value. The R-value is determined by the insulating material's thickness, density, and thermal resistance. The higher the R-value, the better the insulation is at keeping warm air in or out.

These are some of the insulating materials used today:

Fiberglass

Fiberglass insulation can be installed in batts (batt is short for batting; insulation batts are precut sections of insulation designed to fit between wall studs) or loose, in which case the fiberglass is installed using insulation blowing machines.

Polyurethane foam

Foam insulation, also commonly known as spray foam insulation, is a liquid foaming agent that is sprayed into wall cavities, where it expands as it dries.

Mineral wool

Mineral wool insulation is made from either fiberglass, basalt, or, more commonly, steel-mill slag.

Other types of home insulation include recycled plastic fiber, cement-based foam, and structural insulating panels.

Insulation in action

How much use you'll get out of your insulations R-value will depend on its age and the materials used in constructing your house. For example, insulation works better if it's not compressed. Heat will also flow around your insulation through wall studs and joists.

If your home was built using metal framing instead of wood, the heat transference will be greater, and your insulation less effective. If you're in the process of building such a home, insulative sheathing can be placed over the outside of the wall frame to combat thermal transference.

When you were a child, you probably heard your mother say dozens of times that most body heat is lost through your head, so always wear a hat in cold weather. This can also be true of houses.

Hot air not only seeks cooler places, it also rises, so having a good layer of high R-value insulation in your attic can provide great energy savings.

Installing insulation can be a messy task, so you may want to have it done by a professional. An exception would be attic insulation, where laying fiberglass batts on the attic floor between the joists is sometimes all that is necessary.

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