Simple answer: As much as you can fit into a space. But the real answer revolves around the cost of energy and the climate where you live. After all, if it’s 70 degrees all year round, you probably don’t spend a lot of money on energy. And if you cut down your own trees to heat your home, your cost of energy is basically 0.
Unfortunately, most of us don’t live in a perfect climate or have a free source of energy. So we need to keep the heat or air conditioning we pay for in our homes. We use insulation like a giant blanket around our homes to prevent our energy dollars from disappearing.
How Much Insulation Do I Need in my Attic?
The insulation in your attic should be at least 12″ thick. The thicker the better. It is not uncommon to see 15″ to 20″ of insulation in a well insulated attic. If your attic insulation is only a few inches thick or if you can see the ceiling joists, you’re wasting money on your heating and cooling bills.
Upgrading your attic insulation is one of the most cost effective, DIY insulating projects you can do. Adding additional insulation to your attic will save you money by keeping the conditioned air you’ve paid to heat and cool in your home.
How Much Insulation Do I Need in my Walls?
No matter where you live, the walls in your home need as much insulation as you can fit in them. The space inside of your walls should be completely filled with insulation. The insulation should extend from the floor to the ceiling without any gaps or voids in coverage. The wall insulation should wrap tightly around wires, electrical boxes, plumbing and ductwork.
Unfortunately, walls only have a certain amount of space between the studs to put insulation. To beef up the r-value in exterior walls, the U.S. Dept. of Energy is now recommending that builders install foam insulation on the outside of new homes underneath the siding. Adding foam board insulation to the walls of an existing house can only be done during an exterior renovation or siding upgrade.
U.S. Department of Energy Recommended Levels of Insulation
Fortunately, the U.S. Department of Energy put together this fancy chart with recommended levels of insulation for the various climates throughout the country. The recommendations are based on R-values. R-value is a term that measures the effectiveness of insulation at resisting heat transfer. The higher the R-value the longer it takes for heat to pass through your walls and ceilings.