Prepare to Blow Insulation Into Your Attic

A man spraying blown fiberglass insulation between attic trusses, towards the eaves.
  • 2-3 hours
  • Beginner
  • 100-130
What You'll Need
Measuring tape
Soffit vent chutes
Pieces of wood or 10-inch metal flashing

In most older homes and even in some newer ones, blowing extra insulation into your attic can help save you a lot of money on energy bills (some estimates go as high as 20 percent per year), as well as make your home a more comfortable place to live. By far the easiest way to add insulation to a completed home with the walls and ceiling already closed up is to blow insulation into the attic. Cellulose or fiberglass are commonly used as blown insulation. While the process is fairly straight forward, some upfront preparation is necessary. Here's how to get ready to blow extra insulation into your attic.

Step 1 - Gather Your Equipment

Blown insulation (both cellulose and fiberglass) comes in bags and is available at most home and hardware stores. You should also be able to rent a machine to blow the insulation along with 3-inch hoses to carry it up to the attic at the same store. You may even get a bargain since some stores actually provide the equipment for free.

Step 2 - Measure Your Space

Each bag of fiberglass insulation will cover approximately 65 square feet of attic space to a depth of 10 inches (cellulose insulation covers half as much). Ten inches of blown insulation provides an insulating value of approximately R-30 (1-inch of fiberglass provides about R-2.7, while 1-inch of cellulose is approximately R-3).

Measure your attic to determine how many square feet you need to cover. Combine that with the insulation value you want to end up with to determine exactly how much insulation you need to buy. In colder climates, many experts are suggesting you should have at least R-60 in your attic.

Step 3 - Protect the Soffits

You need to make sure you don't block the openings above your soffits at the edge of your roof and the easiest way to do that is to install soffit vent chutes between the studs of your roof. These plastic chutes provide a clear passage for the air coming up through your soffits, allowing it to move up the underside of your roof and maintain proper ventilation in the attic.

Step 4 - Cover the Lights

Many fixtures are not rated to be covered by or even in contact with insulation. So you also need to ensure that insulation doesn't cover the tops of any recessed lighting fixtures that might protrude into your attic. Use 10-inch metal flashing or thin pieces of wood to build boxes around any protruding fixtures, ensuring the walls of the box are at least 3 inches away from the fixture. Be sure the walls are at least as high as the insulation will be when the job is finished.

Before you actually blow insulation in your attic, cover the tops of the boxes to ensure they don't get filled with insulation. You do want to remove the box lids after installing the insulation so air flow can cool the light when it's working.

Safety Tips

Whichever type of insulation you choose to install, there will be lots of small fibers and dust in the air. Be sure you have and wear a respirator, eye protection, and work gloves. A long-sleeved shirt buttoned at the neck will make you feel more comfortable while working and a hard hat will protect your head when you're actually in the attic, blowing the insulation.