New government programs encourage people to make their home more energy efficient and green. Insulation is an important part of an energy efficient home, but more insulation is not always better. Adding insulation and installing insulation in previously uninsulated spaces may be a waste of money and can actually harm your home.
Additional insulation reaches a point of diminishing returns. Before the point of diminishing returns, every dollar spent increasing insulation yields at least a one dollar reduction in energy costs over a reasonable time period. After the point of diminishing returns, every dollar spent yields less than one dollar energy cost reduction over the same time period. An investment in additional insulation does not make financial and energy efficiency sense after the point of diminishing returns.
One place to begin looking for the point of diminishing returns is The International Residential Code (IRC) 2009. The IRC contains minimum insulation requirements for new homes. The IRC required insulation is not at the point of diminishing returns, but it is close. For example, IRC minimum attic insulation in warm climates is R-30. Increasing to R-38 approaches the point of diminishing returns. Exceeding R-38 may pass beyond the point of diminishing returns and may not significantly improve energy efficiency in warm climates.
We have simplified the eight IRC climate zones to three zones because the attic and crawl space insulation requirements are similar for some zones. Where insulation requirements in our zones differ from the IRC requirements, we use the higher requirement. Contact your local building official to determine the insulation requirements in your area.
Our zone one covers the southern one third of the country and includes states such as South Carolina, Florida, Mississippi, Hawaii and most of Texas, Arkansas, Georgia, and California. Our zone two covers the middle one third of the country and includes states such as Virginia, Pennsylvania, Connecticut, Indiana, Illinois, Nebraska, Nevada, and parts of Michigan, Colorado, Utah, and New Mexico. Our zone three covers the northern one third of the country and Alaska.
Minimum attic insulation in our zone one is R-30. Minimum insulation in the floor over a ventilated crawl space is R-19. Minimum attic insulation in our zone two is R-38. Minimum insulation in the floor over a ventilated crawl space is R-30. Minimum attic insulation in our zone three is R-49. Minimum insulation in the floor over a ventilated crawl space is R-30. If the floor framing over a crawl space will not allow for full depth R-30 insulation, then R-19 is acceptable in our zones two and three.
Insulating a ventilated crawl space is more complicated than simply placing insulation between floor joists. This is particularly true in warm and humid climates where insulating floor joists can permit moisture condensation that can damage wood and encourage mold growth. The IRC now allows unventilated and insulated crawl spaces. You should do more research on crawl space insulation and crawl space moisture problems before insulating a crawl space.
More insulation is usually better for improving a home's energy efficiency, up to a certain point. After the point of diminishing returns, investment in other energy efficiency techniques may yield better returns. In new construction these other techniques include passive solar design, air tight construction, high efficiency windows, and attic radiant barriers. In existing homes these other techniques include sealing gaps between the home's interior and exterior and attic radiant barriers.