While insulation is required for all exterior walls in a house, it is not typically required for interior walls. Local and state building codes mandate that new construction homes have adequate insulation in exterior walls and ceilings to suit the local climate.

However, there are several benefits to adding insulation to interior walls. It is excellent for sound-dampening between rooms and can help with temperature control by maintaining a regulated temperature in specific rooms and lowering heat transfer between adjacent areas. Insulating interior walls can also contribute to the overall energy efficiency of your home.

For standard 2x4 walls, the ideal insulation has an R-value between R-13 and R-15. This level of insulation, typically around 3.5 inches thick, fits well within the wall cavity. Common options include fiberglass batts and spray foam. The best choice for your home can depend on your climate; use R-value maps, like those from Energy Star, to determine the recommended level for your region. For colder climates, you might also consider adding exterior insulation for greater efficiency. Always check with your local building codes to ensure you meet any required standards.

Rockwool insulation can last up to 100 years, but just how long this insulation lasts in your home depends on how well it's maintained. Poorly installed insulation may last only 30 years, so be sure to regularly inspect your home's insulation for water damage, settling, and pests to give your insulation the best chance of having a long lifespan.

Spreading tin foil over your windows works similarly to radiant barrier insulation, but not as well. It will reflect some of the sunlight that would otherwise come through the glass and warm up the inside of your home, so it might help a little to keep your home cool in the summer. However, the appearance isn’t preferable to blinds or drapes that can offer the same benefits. You might also consider tinting your windows instead, which is a more aesthetically pleasing change that can still block a good portion of the solar heat coming through your windows.