Blown-in Attic Insulation

outside close-up of attic with window - blown-in attic insulation

Blown-in attic insulation is one of the easiest and most effective ways to conserve energy in your home. It doesn’t require a ton of know-how to install, makes an immediate difference in the amount of energy your home consumes and works year-round to keep your home comfortable.

Unless your home has been built to meet certain energy performance standards, though, it probably doesn’t have the ideal amount of insulation. The gold standard for insulation in attics is R38 to R50, depending on the climate you live in.

The R-value of a material simply refers to its ability to resist heat flow, so the greater the R-value of your insulation, the better it protects against heat loss or gain. The R-value of insulation material is measured per inch and then multiplied by the depth of insulation to get the R-value of a particular space, like an attic.

Most older homes will have insulation with an R-value significantly less than R38 and even new builds won’t necessarily reach that standard. Blown-in insulation can settle over time, so we can’t assume that because a house is fairly new that it’s adequately insulated.

How Effective Is Blown-in Attic Insulation?

The best way to determine the impact blown-in insulation will have on your home and your energy bills is to have a professional energy audit. An energy auditor can figure out how your current level of insulation is performing and how much insulation you need to maximize your home’s energy performance. They can identify leaks in your attic and also advise you on how to seal it properly and get the most benefit out of your investment.

You can expect to shell out a few hundred dollars for a professional audit but there’s a good chance it will be worth it. An audit will help you to make more targeted use of your renovation money and make sure you’re actually putting money and attention into fixing the source of the energy loss.

Generally speaking, though, the impact of properly insulating an attic is big. According to the U.S. Department of Energy, heating and cooling “account for 50% to 70% of the energy used” in a typical American home. The EPA estimates that sealing and adding insulation to the average home can save homeowners “15% on heating and cooling costs and 11% on total energy costs.” The energy performance benefits start right away and your savings will add up over the months and years.

Choosing Insulation

Adding insulation to your attic is something you can hire a professional for but it’s also (typically) a straightforward project that someone of average handiness can do in a weekend. It’s also satisfying and sort of fun, which you cannot say about all home renovation projects. If you decide to DIY, you have basically three options for blown-in insulation:


The R-value is typically 3.2-3.8 per inch. This is the most common type of blown-in insulation. It’s made of recycled paper fibers treated with a substance like boric acid to make it more fire and insect resistant. It’s dense, which will help control air movement in the attic, but Mickey Goodman of This Old House warns that “it can rot and grow moldy if exposed to moisture.” It’s a popular choice because it’s not an irritant like fiberglass, although it’s always advised that respirators, goggles and gloves be worn when blowing in insulation.


The R-value is lower, at 2.2-2.7 per inch. Fiberglass is made of glass and/or sand that’s blown or spun into fibers. It’s the lightest of the three options, which means you’ll need to add more of it to get the R-value you want in your attic. Fiberglass is also a well-known skin and lung irritant. On the other hand, it’s non-flammable, insect resistant and protects the surfaces it’s insulating from moisture.

Rock or Mineral Wool

The R-value here is 3-3.3 per inch. This type of insulation is spun like fiberglass from slag. It’s excellent at blocking air flow and moisture, as well as being naturally fire-resistant. On the downside, it’s more costly than other kinds of loose fill insulation.

When adding new insulation to existing insulation, be aware that you don’t need to add the same type – even if your attic has batt-type insulation, you can blow in insulation on top of it. If you’re adding loose fill to an attic that already has batt insulation, remove any paper or other backing from the batts first.

Things to Consider When Insulating an Attic

attic rafters and windows - blown-in attic insulation

First things first, you’ll need to learn what level of insulation you already have. If you live in a home that doesn’t have enough insulation, you probably know it. Or at least suspect. If you’re not sure, the best way to determine whether your home has enough insulation is to measure it. This handy page from the Insulation Institute explains how to inspect and measure your insulation.

If your insulation is less than R-30, adding more will help you conserve energy and save money on your heating and cooling bills. If you already have an R-30 or greater level of insulation, you might actually be better off putting your money into other energy saving projects. There’s a point where the cost-savings of extra insulation just doesn’t balance out the cost of installing it.

If you have a home that’s quite a bit older, it’s worth your time to have it assessed by a professional who’s knowledgeable in older and historic homes. Older homes were designed to function differently than new ones. They weren’t designed to be air-tight or to keep consistent temperatures. Blocking off air flow in a way the house was not designed to accommodate can lead to bigger problems with moisture and rot.

As a dramatic example, Marcy Giannunzio at The Washington Post explains that older homes built with smaller roof rafters than what would be considered standard today need that warmer attic air to melt rooftop snow and keep the weight from the snow load light. A “fully insulated attic prevents the roof from warming, and the snow can continue to accumulate as it melts at a much slower rate.” This, of course, can spell roof collapse.

This is not to say that older or historic homes can’t be made more energy efficient, but that they require a more systemic, holistic approach that improves performance while taking their design and functionality into account.

Before you add insulation, consider sealing your attic. Not only is a properly sealed attic even more energy efficient; sealing the attic will prevent any condensation issues that might arise from warm air from the main part of your home leaking into the cooler attic space and getting trapped by the insulation.

Make sure you look into any grant or incentive programs that might be running in your area. Many regions will offer financial assistance for homeowners wanting to make improvements that will decrease energy consumption. Those programs might have specific requirements for how the work gets done. Better to find that out beforehand.

Good luck with your project and enjoy your temperature-stable home!

Feature image: Chris Dlugosz; Image 1: Kevin Lam

Written By
More from Mary Read
Tiny Greenhouses You Can Make for Your Tiny Backyard
Those of us not blessed with acres of space for gardening need...
Read More
Join the Conversation

1 Comment

  1. Thank you so much for bringing up energy audits and how they can help you use renovation money much more efficiently. We’ve been meaning to set aside some of our savings to help us renovate our house for the winter season this year since we don’t feel that it’s durable enough to withstand the cold temperatures. To make sure our budget gets put to use better, I’ll get my house audited first before looking for an insulation contractor to follow it up with a fresh new installment of insulating material.

Leave a comment
Leave a comment

Your email address will not be published.