Insulation in the roof and walls is clearly beneficial for its ability to reduce heating and cooling losses and costs. The savings achieved by reducing heat transfer by conduction justifies the cost of adequate insulation.
But don’t forget that convection is another source of heat transfer when air moves between two spaces. Minimizing or controlling losses via convection is desirable but requires more consideration. Adequate outside air is necessary for breathing, and sufficient air transfer is required to ventilate other gases and odors from interior spaces.
Most homes are so leaky that there is plenty of opportunity for air to intrude and be enough for the occupants. However, as structures become more air-tight and interior materials become more synthetic, there is the possibility that the indoor air quality is compromised.
There are several manufacturers of expanding foam insulation who offer various products for the do-it-yourself handyman and small contractor. You might have a small insulation job that does not require the services of a large insulation installer.
There are different products for different purposes. It is important to find the matching product for your job. These products generally come in handy-sized packs or cans and are easy to use.