If you have (only) three-inch batts of insulation in your attic, you likely have an older home that has not had any major energy upgrades. Usually, homes with original three-inch batts have lots of gaps between the batts and the ceiling and have uncovered areas in the attic as well. Adding insulation is relatively inexpensive and has good payback on your investment in an energy efficient home.
How much insulation is "right"?
In much of the South, the code minimum for new homes is R-30. That is about 10 to 12 inches of blown insulation. In the far north, the code minimum for new homes is as high as R-44. That is about 13 to 15 inches of blown insulation.
What to do for your home.
I would add insulation to at least the code minimum. You can get the code minimum number from your local insulation professional. But I would also ask the insulation company what they recommend and get prices on additional inches of insulation.
Insulation has a "declining effect." That means the last inch of insulation has less impact on your home than the first inch. So there are practical limits to the value of insulation, and adding insulation up to the roof of the attic may add no additional discernable utility bill impact than merely adding to R-44.
Prior to adding insulation, seal the thermal bypasses.
One of the bigger problems in existing homes is the one of "thermal bypass." In essence, this means that there are areas of your home where hot or cold attic air can bypass the insulation effect and go straight to the interior your home.
One area you might find this is where there are chaises. An example of a chaise is where you have connections between the home and the attic to facilitate either duct or plumbing stacks (or both). Sometimes, these chaises have larger holes and the hot or cold attic air can pass right through the insulation and impact the interior walls of your home.
Deeply blown insulation (or batts piled high) can block visual observance of thermal bypasses. Insulation offers a resistance to the movement of heat (keeping heat inside the structure in winter; retarding the march of heat to the interior in summer). However, insulation is not an air barrier. Wind can move right through the insulation. This is why it is best to find and seal the thermal bypasses prior to adding insulation.
Seek professional advice.
Also, search Green Home Guide's Find A Pro directory for an energy auditor or other green professional to install your insulation. You are looking for a company that understands the impacts in your specific market and with your area's weather conditions. You may need some help in identifying and repairing the attic's thermal bypasses.
Other areas where you may want to be careful prior to adding insulation:
- Electrical - Depending on the age and condition of your electrical wiring, you may want to consider having it evaluated and upgraded prior to adding many inches of insulation.
- Can lights - Many homes have can lighting, where the fixture receptacle is recessed into the ceiling (or into the attic space). Many of these lighting fixtures have ventilation holes into the attic (a kind of thermal bypass) and transfer heat from the fixture to the attic. Covering these electrical fixtures in the attic with many inches of insulation runs the risk of heat buildup in the fixture with potential negative impacts. You may want to discuss with an energy or electrical professional the impacts and what your options may be with regard to the can lighting.
Insulation is relatively cheap and relatively easy to do. You will be well served by a thorough survey of items in your attic that could be improved or repaired prior to being covered up in insulation.
There are usually good paybacks on an investment in additional insulation. Add at least up to the code minimum in your area, and it can't be very expensive to add 3 to 6 inches of additional R-value on top of the code minimum.
Check to see if there are local, state or national tax incentives, rebates or utility incentives to help you pay for the value of adding insulation to your home.