Courtesy of MD Home Inspection
Nearly 90% of homes may be under insulated, due to insulation standards rising over the years. Adding insulation to proper levels can significantly lower your utility bills enough to pay for the cost within a few years.
Here is a general guideline to determine the adequacy of your attic insulation:
1) Determine your insulation type
Most homes in southeastern Michigan have fiberglass batt insulation (which come in large rolls and are laid out in strips) or one of a variety of blown-in or loose insulation.
Your attic may contain more than one type of insulation, which may be the result of attempting to further insulate with a different type without removing the original insulation.
*Some attics have vermiculite insulation, which may contain asbestos (prior to 1991). Vermiculite is a lightweight, pea-sized, flaky gray mineral (see close-up photo to the left).
Do not disturb vermiculite insulation unless you have it tested by an approved lab to be sure it does not contain asbestos. Contact your local health department for the name of an approved lab.
For more information, see the following EPA link: EPA Vermiculite Information.
2) Measure your insulation depth
With a ruler or tape measure (a rigid ruler works best), determine the insulation depth in inches. If you have significant higher and lower elevations of insulation, it should be leveled (try to measure the average level).
*Tips – only step on walk-boards or attic joists (do NOT walk on insulation) or your foot may end up waving hello to the folks in the room below.
The previous insulation installer may have left a ruler stick or indicator of your insulation level – make sure that the stick is fully penetrating to the base of the insulation to ensure the reading is accurate.
3) Calculate your attic’s “R” value
Attic insulation is measured by it’s “R” value, which is its capacity to resist heat flow.
After determining the insulation type and depth, use the chart to the left to calculate your attic insulation’s R value.
Example: if you have 8 inches of blown-in cellulose, 8 x 3.7 = 29.6 R value.
The 2015 IECC building code recommendsR38-R49 for homes in our southeastern Michigan climate, depending on heating fuel type. Natural gas is R38 and propane, electric, and oil fuel source heating is R49.
If your insulation is below the applicable R value, the recommendation is to add insulation.