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. Here are 5 frequently asked questions about insulation.
1. Why am I getting condensation on my wall?
- Condensation occurs when warm air reaches a cold surface that is below the dew point temperature.
- Dew point temperature is the temperature at which the initial interior air reaches 100% RH.
- In the heating season, the interior side of the sheathing (OSB, plywood, gypsum, etc.) is typically the first condensing surface.
- In the cooling season, the condensing surface is typically on the interior side of the assembly. For example, the condensation buildup that is sometimes noted on the polyethylene vapor barrier.
- The proper ratio of exterior to cavity insulation, will keep the condensing surface above the dew point temperature and reduces the risk of condensation.
2. How much energy is saved when I upgrade my insulation?
The energy consumption of an entire building is dependent on all the components of the building, considered as a system; including the insulation, window performance, mechanical systems and building use.
Increasing the amount of insulation will decrease the heat flow through that component of the enclosure, and in turn, reduce the heating and cooling demand. Adding insulation can also create a more comfortable indoor environment, when in conjunction with high performance windows.
Note that the overall energy savings will depend on the building system and the amount of heat flow reduction does not directly translate to the amount of savings.
3. How can I use vapor permeable insulation in hot/humid climates?
In hot and humid climates, inward vapor drive is a concern, especially in combination with reservoir claddings such as brick or masonry. When using vapor permeable insulation, it is recommended to use a semi-permeable (~10 perm or less) water-resistive barrier on the substrate, behind the insulation. This strategy will reduce the amount of vapor entering the interior of the wall while allowing for drying if necessary.
4. How do I calculate effective R-Value or assembly R-Value?
Every material or layer in an assembly has a thermal resistance, known as R-value. The R-value has a direct relationship with the material’s thickness. The sum of all material R-values is the total nominal R-value of the assembly, including surface air films. However, the total effective R-value of an assembly is the total nominal R-value minus reductions caused by thermal bridging at the studs, girts, fasteners, ties and other attachment methods.
5. What is the ratio of exterior to interior insulation that I should use to ensure the dew point is on the exterior?
The level of exterior insulation required to move the dew point to the exterior side of the assembly will depend on the assembly type, insulation type specified, and climate. As a best practice rule of thumb, a minimum exterior to interior R-value ratio of 3:1 should be applied.