Insulation is one of the most effective ways to improve a building’s energy efficiency and lower its heating costs. Insulation prevents heat from moving upwards or downwards through the walls, roof and other surfaces.
There are a wide variety of insulation materials ranging from bulky fiber materials to sleek foils. Each has its own thermal resistance rating.
U-Value
The U-Value is a standard measurement of heat transfer through a building element, such as an external wall, window or floor. It’s calculated from the thermal resistances of the layers which make up that element, plus an internal and external surface (Ri and Ro respectively) and their associated thermal conductivity (lambda ‘l’).
A low U-Value indicates good performance as an insulator and can help reduce energy consumption. The lower the U-Value, the less heat is lost through conduction and convection, and the more the insulation resists radiation. However, workmanship and installation standards can strongly influence a structure’s overall thermal transmittance, as gaps or cold bridges will reduce the effectiveness of insulation materials.
It’s important to note that U-Value calculations don’t take other modes of energy loss into account – air leakage, for example. This is why it’s important to ensure that your insulation is installed correctly and well-fitted, with no gaps or draughts.
The calculation of a U-Value is relatively straightforward, with a material’s thickness (d) and its thermal conductivity or ‘l’ value being taken into consideration. However, in reality, it can get more complicated when multiple layers are present, or when ventilation cavities or inclined elements are involved. In addition, it is often necessary to consider the effect of the environmental temperature on a material’s thermal properties.
R-Value
As energy efficiency is becoming more of a concern, builders and homeowners are looking into the specific attributes and performance of the materials used in their homes. R-Value is one such measurement that is often given a lot of attention when determining the best types of insulation for different applications. R-Value measures the thermal resistance of a material, which is the inverse of thermal conductance.
The higher the R-Value, the greater the insulating properties of a material. However, the exact R-Value will vary depending on the thickness and type of insulation, and other factors can also affect its effectiveness. For example, if a layer of insulation is compressed, its R-Value will decrease because the thicker materials provide less protection against heat flow.
Furthermore, R-Value does not measure other components of a building that restrict the transfer of heat, such as studs or windows. As such, even if a wall is properly insulated with the recommended R-Value, it may still lose heat through air leakage.
When it comes to evaluating the R-Value of insulation, a more holistic approach is necessary. Incorporating realistic fuel escalation rates and replacing appliances on 15-year cycles will help to account for the cost of a home’s energy consumption, allowing for more accurate R-Value recommendations. This will ensure that the homeowner’s home stays well insulated and saves on energy costs.
Air Leakage
The airflow into and out of a home or commercial building is caused by pressure differences between internal and external environments. This airflow can cause moisture to leak into the walls and thermal envelope. Moisture accumulation can damage insulation and introduce pollutants into living spaces.
The good news is that controlling air leakage can lower energy bills and improve occupant comfort. ENERGY STAR estimates that as much as 20 percent of heated and cooled homes’ energy usage is wasted due to air leakage through the building envelope.
A professional home energy audit with an infrared camera and a blower door test can identify air leaks. The test forces a high volume of air into the home, which highlights areas where expensive air leakage exists. These areas can include attic access hatches, wall and floor joists, windows and doors. Sealing these gaps with caulking, expanding spray foam or house flashing can reduce energy costs and promote occupant health.
The duct system can also be a major source of air leakage. Leaking ducts can result in significant loss of conditioned air and reduce the efficiency of forced air systems. This problem is easily corrected by repairing and sealing the ducts, replacing the ductwork with more efficient insulated ductwork or installing new ductwork altogether. Air sealing is a critical component of the Home Performance philosophy.
Energy Efficiency
Having the correct insulation in place in your home is one of the best ways to reduce energy costs. This is because heat loss in winter and heat gain in summer are lessened, and thereby so is the amount of energy needed to maintain thermal comfort. Insulation is also a good way to reduce environmental impact by reducing the need for fossil fuel consumption and associated GHG emissions.
Insulation is available in many different materials, ranging from bulky fiber products such as fiberglass, rock wool, and cellulose to rigid foam boards to sleek foils. The material used determines the R-value and the corresponding level of energy efficiency. Bulky insulation materials trap air or another gas in their cells to resist conductive heat flow, while reflective insulation systems trap radiant heat by reflecting it back away from living spaces.
It’s important to remember that the performance of insulation degrades over time, which is why it needs to be regularly checked and maintained. Using a proper maintenance system will ensure that your insulation retains its R-value and thermal resistance and prevents leakage.
Generally, the most effective time to fit insulation is during construction or major renovations when it’s easier to install. However, it can be retro fitted without major inconvenience in some cases. Adding insulation to existing homes is relatively inexpensive, but it’s important to check with the local authority for the most appropriate products for your climate.