Most Chicago-area attics need R-49 to R-60, which is roughly 14 to 18 inches of blown-in fiberglass. The Department of Energy places our region in Climate Zone 5, where that range is the target for existing homes. Anything under about 8 inches is thin for this climate. If you can see the tops of your ceiling joists above the insulation, you do not have enough.
How much attic insulation do I need is a question we field every September, usually the morning after the first genuinely cold night. It is a fair thing to ask, because this is one of the few home upgrades where the correct answer is a number you can check yourself with a tape measure.
Most houses around here were insulated to the code in force the year they were built. For anything built before 2000, that number was lower than what we use today. That does not automatically mean your attic needs work.
How much attic insulation do I need in the Chicago area?
The Department of Energy recommends R-49 to R-60 for attics in Climate Zone 5, which covers Cook, Lake and DuPage counties. ENERGY STAR pushes the top of that range and recommends R-60. R-value measures resistance to heat flow, so a higher number means the ceiling holds heat in longer.
Translated into depth, R-49 is about 14 inches of blown fiberglass. R-60 lands closer to 18 inches. Cellulose is a little denser and reaches the same values an inch or so shallower.
How do I measure the insulation I already have?
A tape measure and a flashlight answer this in about ten minutes. Push the tape down through the fill until it touches the drywall below, and read the depth in three or four spots rather than one.
- Standard ceiling joists are 2x10s, which are 9.25 inches deep. Fill level with the joist tops is roughly R-30.
- Insulation only halfway up the joists is closer to R-19, which is well short.
- Check near the eaves, where the fill is almost always thinner than in the middle.
- Look for gaps around the attic hatch, recessed lights and bathroom fans.
- Note any spot that is matted down, stained or damp before you add anything.
Should you add on top or remove the old insulation first?
In most attics you add new insulation directly over the old, and that is both cheaper and perfectly sound. Old fiberglass does not expire. It loses value only when it is compressed, wet, or contaminated.
Top it up
- Existing fill is dry and loose
- No rodent droppings or nesting
- No stains from past roof leaks
- You simply have too little depth
Remove it first
- Insulation is wet or smells musty
- Rodent contamination is present
- Visible mold on the roof sheathing
- Fire or smoke damage
If anything in the second column applies, read our guide to attic insulation removal before you buy a single bag. Adding clean insulation over contaminated insulation just seals the problem in.
What does adding attic insulation actually save?
ENERGY STAR estimates homeowners save an average of 15% on heating and cooling costs by air sealing and adding insulation in attics, crawl spaces and rim joists. Notice that the estimate pairs the two together. Sealing the gaps around light fixtures and the attic hatch does real work in that number, and depth alone underperforms it.
On pricing. National figures for blown-in attic insulation run about $1.00 to $3.00 per square foot installed, and jobs that need removal or hard access sit higher. We quote only after someone has been in your attic, because square footage alone will not tell you whether the eaves are blocked or the hatch leaks.
When you do not need more attic insulation
If you already measure 14 inches or more of even, dry fill and your upstairs rooms hold temperature, your money is better spent elsewhere. In Glenview last winter we measured a 16-inch attic for a homeowner who was braced for a quote, and told him to keep it. An attic already at R-49 does not get meaningfully better at R-60.
The bigger wins in that situation are usually air sealing, restricted ductwork, or a system that is not moving air evenly. Uneven room temperatures point at duct condition and heating and cooling balance more often than at insulation depth.
Frequently asked questions
How many inches of attic insulation do I need?
Around 14 to 18 inches for the Chicago area, depending on the material. Blown fiberglass reaches R-49 at roughly 14 inches and R-60 at about 18, while cellulose hits the same values an inch or so shallower. Measure in several spots, because attic fill is rarely even.
Can I put new insulation over old attic insulation?
Yes, in most attics. Loose fiberglass and cellulose can be topped directly, and unfaced batts can be laid across the joists over existing fill. The exceptions are faced batts, whose paper vapor barrier traps moisture when buried, and any insulation that is wet, moldy or rodent contaminated.
Is blown-in or batt insulation better for an attic?
Blown-in usually wins in an existing attic. It flows around wiring, pipes and irregular joist spacing, where batts leave gaps that quietly undo much of their rated value. Batts make more sense in new construction with clean, consistent bays and nothing in the way.
How do I know if my attic insulation is bad?
Look for insulation that is matted flat, damp to the touch, or carrying rodent droppings. Dark streaks across the surface usually mean household air is being pulled through it, which points at a sealing gap rather than a depth problem. Any musty smell is worth investigating before you add more.
If the tape says you are short, our attic insulation services page covers what a top-up job involves. Top Air Solutions has worked in Chicagoland attics since 2008, and we hold a 4.9 star rating across 810+ reviews.
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Not sure how deep your attic really is?
We have been measuring Chicagoland attics since 2008, and we will tell you when you already have enough.