Optimizing your home’s insulation is one of the best ways to reduce heating and cooling costs and dramatically raise the comfort level in your home. There are many options:
- fiberglass (batt and roll)
- concrete block insulation and insulating concrete blocks
- foam board or rigid foam
- insulating concrete forms
- loose fill and blow in
- reflective systems
- rigid fibrous or fiber insulation
- sprayed foam and foamed-in-place (open or closed cell)
- structural insulated panels (SIPS)
The most common forms of insulation used today in residential projects are blanket fiberglass (batt and roll) and spray foam.
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.
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. 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.
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.
No discussion of insulation would be complete without mention of infiltration, or the amount of air leakage in a home. Infiltration is measured in air changes per hour (ACH). Many homes in the US have an ACH of over 1.5. An ACH of 1.5 means the homes HVAC system must condition 1.5 times the entire volume of the homes air per hour. For example if its 20 degrees outside and you desire a 70 degree interior, your heating system must raise the temperature of 1.5 times the volume of your entire home 50 degrees every hour. This can result in very high heating bills.
The most common and widely available type of insulation — comes in the form of batts or rolls. It consists of flexible fibers, most commonly fiberglass. You also can find batts and rolls made from mineral (rock and slag) wool, plastic fibers, and natural fibers, such as cotton and sheep’s wool.
Batts and rolls are available in widths suited to standard spacing of wall studs, attic trusses or rafters, and floor joists. Continuous rolls can be hand-cut and trimmed to fit. They are available with or without facings. Manufacturers often attach a facing (such as kraft paper, foil-kraft paper, or vinyl) to act as a vapor barrier and/or air barrier. Batts with a special flame-resistant facing are available in various widths for basement walls and other places where the insulation will be left exposed. A facing also helps facilitate fastening during installation. However, unfaced batts are a better choice when adding insulation over existing insulation.
Standard fiberglass blankets and batts have a thermal resistance or R-value between R-2.9 and R-3.8 per inch of thickness. High-performance (medium-density and high-density) fiberglass blankets and batts have R-values between R-3.7 and R-4.3 per inch of thickness.
SPRAYED-FOAM AND FOAMED-IN-PLACE INSULATION
Liquid foam insulation materials can be sprayed, foamed-in-place, injected, or poured. Some installations can have twice the R-value per inch of traditional batt insulation, and can fill even the smallest cavities, creating an effective air barrier to reduce infiltration. This is not measured in the insulations R-value but makes a big difference in effectiveness. Spray foam fills many air leakage cracks and creates more effective thermal insulation than its R-value alone.
TYPES OF LIQUID FOAM INSULATION
Today, most foam materials use foaming agents that don’t use chlorofluorocarbons (CFCs) or hydrochlorofluorocarbons (HCFCs), which are harmful to the earth’s ozone layer.
Available liquid foam insulation materials include:
- Polyisocyanurate (polyiso)
Some less common types include Icynene foam and Tripolymer foam. Icynene foam can be either sprayed or injected, which makes it the most versatile. It also has good resistance to both air and water intrusion. Tripolymer foam—a water-soluble foam—is injected into wall cavities. It has excellent resistance to fire and air intrusion.
(courtesy of energy.gov)
BEFORE YOU INSULATE? Know your Home’s Thermal IQ
Homeowners may fall prey to sales pitches when choosing insulation. Insulation is just one part of making your home more energy efficient (cost savings) and comfortable. Before handing over your credit card, the Alexander Group recommends a home energy audit. Installing new insulation before you understand your home’s thermal IQ may be a waste of money – you may have hidden leakages and other systems like windows, doors, exhaust, ventilation or HVAC systems which may be under performing.