Insulation

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Photo of a man blowing insulation into a hole drilled into a wall.
Dennis Schroeder / NREL

Insulation in your home provides resistance to heat flow and lowers your heating and cooling costs. Properly insulating your home not only reduces heating and cooling costs, but also improves comfort.

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.

R-Values

An insulating material’s resistance to conductive heat flow is measured or rated in terms of its thermal resistance or R-value -- the higher the R-value, the greater the insulating effectiveness. The R-value depends on the type of insulation, its thickness, and its density. The R-value of some insulations also depends on temperature, aging, and moisture accumulation. When calculating the R-value of a multilayered installation, add the R-values of the individual layers.

Installing more insulation in your home increases the R-value and the resistance to heat flow. In general, increased insulation thickness will proportionally increase the R-value. However, as the installed thickness increases for loose-fill insulation, the settled density of the product increases due to compression of the insulation under its own weight. Because of this compression, loose-fill insulation R-value does not change proportionately with thickness. To determine how much insulation you need for your climate, consult a local insulation contractor.

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. The overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself because heat flows more readily through studs, joists, and other building materials, in a phenomenon known as thermal bridging. In addition, insulation that fills building cavities densely enough to reduce airflow can also reduce convective heat loss.

Unlike traditional insulation materials, radiant barriers are highly reflective materials that re-emit radiant heat rather than absorbing it, reducing cooling loads. As such, a radiant barrier has no inherent R-value.

Although it is possible to calculate an R-value for a specific radiant barrier or reflective insulation installation, the effectiveness of these systems lies in their ability to reduce heat gain by reflecting heat away from the living space.

The amount of insulation or R-value you'll need depends on your climate, type of heating and cooling system, and the part of the house you plan to insulate. To learn more, see our information on adding insulation to an existing house or insulating a new house. Also, remember that air sealing and moisture control are important to home energy efficiency, health, and comfort.

Map of the United States showing recommended R-values for different regions. Please contact consumer.webmaster@nrel.gov if you need assistance reading this map.

All of Alaska in Zone 7 except for the following Boroughs in Zone 8:

  • Bethel
  • Dellingham
  • Fairbanks N. Star
  • Nome
  • North Slope
  • Northwest Arctic
  • Southeast Fairbanks
  • Wade Hampton
  • Yukon-Koyukuk

Zone 1 includes Hawaii, Guam, Puerto Rico, and the Virgin Islands.

  Add Insulation to Attic    
Zone Uninsulated Attic Existing 3-4 Inches of Insulation Floor
1 R30 to R49 R25 to R30 R13
2 R30 to R60 R25 to R38 R13 to R19
3 R30 to R60 R25 to R38 R19 to R25
4 R38 to R60 R38 R25 to R30
5 R49 to R60 R38 to R49 R25 to R30

 

 

 

 

 

 

Wall Insulation:

Whenever exterior siding is removed on an uninsulated wood-frame wall:

  • Drill holes in the sheathing and blow insulation into the empty wall cavity before installing the new siding, and
  • Zones 3-4: Add R5 insulative wall sheathing beneath the new siding
  • Zones 5-8: Add R5 to R6 insulative wall sheathing beneath the new siding.

Whenever exterior siding is removed on an insulated wood-frame wall:

  • For Zones 4 to 8: Add R5 insulative sheathing before installing the new siding.

* These recommendations are cost-effective levels of insulation based on the best available information on local fuel and materials costs and weather conditions. Consequently, the levels may differ from current local
building codes.

Source: ENERGY STAR

Types of Insulation

To choose the best insulation for your home from the many types of insulation on the market, you’ll need to know where you want or need to install the insulation, and what R-value you want the installation to achieve. Other considerations may include indoor air quality impacts, life cycle costs, recycled content, embodied energy, and ease of installation, especially if you plan to do the installation yourself. Some insulation strategies require professional installation, while homeowners can easily handle others.

Insulation Materials

Insulation materials run the gamut from bulky fiber materials such as fiberglass, rock and slag wool, cellulose, and natural fibers to rigid foam boards to sleek foils. Bulky materials resist conductive and -- to a lesser degree -- convective heat flow in a building cavity. Rigid foam boards trap air or another gas to resist conductive heat flow. Highly reflective foils in radiant barriers and reflective insulation systems reflect radiant heat away from living spaces, making them particularly useful in cooling climates. Other less common materials such as cementitious and phenolic foams and vermiculite and perlite are also available.