exterior, floor, roof and interior wall insulation
Installing interior wall insulation along with floor, exterior, and roof insulation is really important to make a home energy efficient. This is more important now than it has ever been considering the cost of electricity continues to climb.
The R-value of insulation is usually related to its thickness and density. The higher the R-value, the better the insulation properties will be.
Most building codes have a minimum exterior wall code of R-11. This is for 2x4 walls, but many modern homes are now built with 2x6 walls and the R-value can be R-19. This makes a big difference for heating and cooling a home and making it more efficient.
It's also important when you're insulation the walls to insulate between the boards used for window and door headers. This is a place where a lot of heat escapes. Headers usually have about an 2 1/2-inches of space between them.
The walls need to have as much insulation as you can stuff in there. Insulation batts for walls and floors come in sizes that fit between either 16-inch walls or 24-inch walls.
Wall insulation is essential, but there are also other areas in the walls that lose heat. Outlet and switch boxes on exterior walls can only get a little insulation behind them, so they need to be insulated with a special outlet and light switch insulation kit.
Older water heaters were not properly insulated so if you have an older water heater it would be best to just replace it instead of buying a water heater jacket.
Also older heating ducts that aren't insulated should be wrapped up to prevent heat loss.
interior wall insulation
Next, floor, roof and attic insulation