The purpose of home insulation is to control the transfer of heat. Depending on the weather, the goal is to either keep the heat in or out of our homes. Although scientifically it is impossible to actually stop the transfer of heat (it will always find a way to move to a lower-temperature area), we can slow it down considerably.
By providing resistance to heat flow and slowing the transfer of heat, home insulation keeps the temperature inside the home at more moderate levels. This increases comfort and decreases energy usage.
So how does insulation resist heat flow?
To understand how insulation slows the rate of heat transfer, it is helpful to recognize the three different kinds of heat flow:
- Conduction is the way heat transfers between materials that are in direct contact with each other, molecule to molecule. When a cold metal spoon becomes hot to the touch after being placed into a cup of hot coffee, this is heat transfer by conduction.
- Convection refers to the movement of heat in a gas or liquid. The colder particles sink (due to increased density and the effect of gravity) therefore moving the warmer particles higher. Convection is why air in the attic is warmer than air in the basement.
- Radiation does not involve particles or need any contact between materials to transfer heat. Radiant heat travels in a straight line, heating anything in its path that is solid and able to absorb its energy. Heat from the sun or a light bulb are examples of radiant heat transfer.
Regardless of what type of heat flow is occurring, heat will always move from warmer to colder areas until the temperature is the same in each place. In the winter, heat flows from heated areas of the home into unheated spaces such as basements, garages, attics, and the outdoors. This is reversed in the hotter summer months when heat flows from these same spaces into the house. Heat will also move through interior ceilings, floors, and walls – any place there is a difference in temperature. Proper insulation slows this natural heat flow and allows HVAC systems to economically replace or remove the heat that was lost or gained.
Most home insulation slows conductive and convective heat flow. Radiant barriers and reflective insulation are also used. These work by reflecting radiant heat rather than absorbing it, reducing the cooling load in the warmer months.
The amount of thermal resistance a material has is expressed as its R-value. The higher the R-value, the better the insulation. Several factors can contribute to R-value:
- Type of insulation
- Installation method & location
- Moisture accumulation
Generally, adding more insulation will increase the R-value. If multiple layers are installed, add up the value of each layer to calculate the total R-value. One exception to this rule is when using loose-fill insulation. Due to this type of insulation compacting to a certain degree under its own weight, its R-value does not increase proportionately with thickness.
When installing, care should be taken to ensure insulation is not unnecessarily compressed as this decreases the stated R-value. Thermal bridging (heat flowing more easily through certain building materials such as studs and joists) should be taken into consideration as well as filling empty building cavities to reduce airflow and leakage. Each factor of proper home insulation works together to slow heat transfer, reduce energy usage, and keep the interior at a comfortable temperature.
Sound complicated? Give us a call and we will determine the best insulation to fit your needs. We have decades of experience with All Types of insulation best suited for Southern California.