Depending of the type of construction and the area where you live, walls can account for 10 to 30 percent of heat loss in houses. Not to mention the cracks and penetrations that allow uncontrolled air leakage into and out of the house.
Installing insulation in your walls during the process of building or renovating a house increases the energy efficiency of the building, which saves money on heating and cooling. Insulation also buffers sound.
Exterior walls should be insulated to maximum R-value, which is determined by the thickness of the stud wall. Insulating exterior walls is an easy do-it-yourself project.
New Construction or an Addition
Warning: DO NOT INSTALL fiberglass insulation without wearing the proper protective gear. Use a dust mask to prevent inhalation of fiberglass and other particles, use goggles to shield your eyes, and wear gloves and a long-sleeved shirt to avert itchiness caused by fiberglass contact on the skin.
1] Your exterior walls will be comprised of either 2 x 6 or 2 x 4 studs. 2 x 6 stud walls allow for more insulation because of their extra depth. Use batts of fiberglass insulation for new construction or a room addition.
A batt is similar to a blanket, but a batt is pre-cut in specific lengths.
A blanket comes in certain widths but the length must be cut and is best for a wall without studs, like a basement wall.
2] Take pre-installation measurements. Measure the height of your walls and the width between studs.
3] Determine the correct R-value you need for exterior walls in your location. There are various grades of batts for different locations in the house (interior, exterior, attic or basement). The R-value of the batt is a meter of the thermal resistance. The higher the R-value, such as R-30 or R-36, the more effectively the batt insulates.
4] Choose faced or non-faced batts. Faced batts are covered on the front of the fiberglass to make the process of installation easier. The facing material is also retards vapor.
5] For 2 x 6 studs. Depending on local codes or your desired R-value for the wall, you may use 5 1/2 inch thick R-21. R-19 fiberglass batt insulation (6 1/4 inch thick) can also be used.
6] For 2 x 4 studs. Choices are R-15 or R-13, both of which are 3-1/2 inches thick.
7] Using a utility knife cut the batts to the size of the wall cavities.
8] Place each batt into the cavity and staple the batts to the studs. However, inserting all the insulation first and then stapling the batts down all at once is the most efficient installation method.
9] As you place batts in the cavities, you may find outlets or plumbing in the way. You will need to cut the batts around those fixtures.
Note: Most of the insulation property comes from the air trapped between the fiberglass fibers, not the fiberglass itself. Because of this, squeezing a larger amount of insulation into a small cavity does not increase the amount of insulation (the R-value). In fact the tighter you compress the insulation the lower the R-value.