The Insulation Calculator: How Much
& How Do You Afford It?

Before you use this insulation calculator, please familiarize yourself with the easy to understand principles of heat flow and types of insulation you may have already in your home and those from which you may choose to supplement, based on effectiveness, price and ease of installation.

How Much Do You Need?

The insulation calculator is a three step process requiring you, a screwdriver and a ruler.

First, measure the insulation depths you now have. For attic insulation, this should be straightforward. For wall insulation, unscrew an electrical socket plate or light switch plate at various locations to measure. For floor insulation, do the same with a ceiling light fixture or by removing a suspended ceiling panel.

If you can’t see the R-value printed on any of the insulation you now have, use this chart to calculate it.

The second step of the insulation calculator just involves pushing buttons. Now that you know the type and depth of home insulation you have, find out how much you need using the DOE Climate Zone insulation calculator.

Let’s say you now have 4 inches of rock wool attic insulation. Using the chart above, it’s R-value is 4 x 2.8 = 11.2. If you live in Zone 5, you should have R=41 in attic insulation. Therefore, you need to add R=30 in additional insulation.

Since rock wool provides 2.8 in R value per inch, the 30R you need divided by the 2.8R/inch=10.7 more inches.

You should add it directly over the existing insulation. If feasible, place it perpendicular to the existing attic insulation to further limit heat flow.

Sealing Cracks

Just adding home insulation is not enough. It is important to limit the flow of warm, moist air into or out of your house. In summer an air leak will carry warm, humid air inside. In winter, a leak will carry moist warmer air from your bathroom into your attic, where the moisture may condense and contribute to rot. Seal these leaks before you insulate, when you can best see and feel them.

Look for gaps where two walls meet, and around doors, windows, fireplaces, electrical fixtures or duct chases. Caulk and spray foam insulation are excellent for smaller openings. For large gaps, you can stuff some fiberglass batt insulation to block air flow. Glass fireplace doors are an inexpensive way to limit outward air flow, since the chimney flue is not very air tight.

Affording It

Finally, assess where your insulation dollars will be most effective. Since warm air rises and cool air sinks, insulating your attic and your basement or foundation slab give you the best return on your investment. For your walls, windows are by far the greatest area of heat gain or loss. Instead of investing thousands to upgrade to double or triple glazed windows, look into lined curtains or insulated blinds. Consider using outdoor shading and wind blocking to improve the performance of your home’s insulation.

Even in these fiscally tight times, there are state and federal incentives and rebates to promote renewable energy and energy efficiency. As a general rule, you can expect to recover the cost of insulating your home in 5-6 years, assuming fuel costs stay the same. As fuel costs rise, this recovery period will be shorter.

When planning your budget, remember to include the increase in home value you will enjoy with a more efficient home.

For more information, visit this excellent home insulation site.

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