Blown-in insulation can last a long time—but not forever. If your house has cold spots, uneven temperatures, or heat gain in the summer, you might have inadequate insulation or your insulation quality might be past its prime. Many homes, especially older ones, don’t have proper insulation to begin with. If you’re wondering whether your attic space needs more, or if you can do it yourself, here’s what to consider before piling on an extra layer of insulation.
How Long Does Blown-In Insulation Last?
Blown-in insulation doesn’t have an expiration date, but that doesn’t mean it lasts forever. Over time, you can lose insulation effectiveness if it settles, shifts, or even gets damaged by moisture from roof leaks or pests. "If your home is more than 15 years old and has not had an upgrade to its insulation, it may be time for replacement," recommends Andrew Legge, CEO of Havelock Wool.
Most homeowners should check their attic insulation every 10 to 15 years, though some types can last longer if undisturbed. Cellulose insulation, for example, tends to settle more than fiberglass types of insulation. This can create air pockets and gaps that let heat escape.
If your home is over 20 years old and hasn’t had an update, there’s a good chance you’re due. Even if your insulation is technically “still there,” it may not be doing much anymore. Adding more can help with comfort and reduce energy bills.
What Are the Types of Blown-In Insulation?
There are a few kinds of blown-in insulation materials, and each has a different R-value per inch. The R-value tells you how well the material resists heat transfer—the higher the number, the better the insulation.
The total R-value depends on how deep the insulation is blown in. For example, if you want an R-38 rating (common in attics), you’ll need more inches of fiberglass than cellulose.
Here’s a quick comparison:
- Loose-fill fiberglass insulation
R-value: ~2.2 to 2.7 per inch
Light and fluffy, doesn’t settle much, but not great at blocking air leaks unless packed well. - Loose-fill cellulose insulation
R-value: ~3.2 to 3.8 per inch
Made from recycled materials (mainly newsprint paper), treated for fire resistance. Denser than fiberglass, good at blocking air leaks, but can settle more over time. - Mineral wool insulation (rock wool or slag wool)
R-value: ~3.0 to 3.3 per inch
Fire-resistant and water-repellent. Less common and usually more expensive, but works well in soundproofing too.
Can You Add More on Top of Old Insulation?
Yes, you can. In fact, layering new insulation over old is common. It’s usually safe as long as you don't have wet insulation and it's free of mold growth or pests. You don’t need to remove it unless there’s a clear problem. That saves time and cost.
Before you blow in more insulation, take a quick check:
- Visible damage: Does the existing insulation have water damage or growth of mold?
- Pest infestation: Are there signs of varmints or insects?
- Attic floors: Can you see the attic floors/floor joists/ceiling joists clearly?
If the answer to any of these insulation issues is yes, you may want to do insulation removal first. Otherwise, you’re fine to blow more on top. You’ll just want to stick with the same type—blowing cellulose over cellulose, or fiberglass over fiberglass—so it settles evenly.
DIY Installation or Hire It Out?
Blown-in insulation can be a DIY project; however, it’s not for everyone. You can rent a blower from most home improvement stores, often for free with purchase of insulation. Still, it’s a dusty and messy project, especially if you’re crawling around in a tight attic.
If you go the DIY route, be sure to wear protective gear, a mask, goggles, and long-sleeve clothing. Even cellulose, which is made from recycled paper, can irritate your lungs and skin during the installation process. Also be sure not to block your soffit vents.
Here’s when it makes sense to call in an insulation contractor:
- Your attic space is hard to access or has hard-to-reach areas
- You're worried you'll break through the ceiling (it happens)
- You’re not comfortable working around wiring or fixtures
- The current insulation may have mold or rodent infestation or waste
- You want the job done quickly and evenly
FAQs
Is there an easy way to know if I need more insulation?
Earlier this year, HSFTOOLS released the Finder S2 thermal image camera and sent us one to test. Within minutes, we could tell exactly where our insulation was lacking! Scary, really. If you have access to a thermal camera, use it. But to really be sure, you can contact a local company to do an energy audit to help you find ways to increase the energy efficiency of your home. This energy assessment can help determine what energy upgrades you can do to your home to reduce your energy costs, create a more energy efficient home, and reduce your carbon footprint in the process.
Is it bad to have too many inches of insulation in the attic?
It’s rare, but it can happen. Too much loose-fill insulation can block attic ventilation. Without proper ventilation from the soffits to the roof, you can trap moisture and cause mold and ice dams in the winter. You want a balance: enough to keep your living space warm or cool, but not so much that your vents are blocked and your attic can’t breathe.
What’s the difference between cellulose and fiberglass blown-in insulation?
Cellulose insulation is made from recycled paper and treated for fire resistance. It’s heavier and can settle more over time. Fiberglass is made from spun glass fibers. It’s lighter and doesn’t settle as much, but it can irritate your skin and lungs. Both insulation types work well when installed to the right depth.
