How to Install Blown-In Attic Insulation

Blown-in insulation is the fastest way to add real thermal protection to an under-insulated attic. Unlike roll insulation, it fills every cavity, settles into corners, and conforms around pipes and wiring without gaps. The work is straightforward enough for a homeowner, but there's a difference between spreading insulation and installing it to code depth—and that difference shows up in your heating and cooling bills. This guide walks you through the mechanics: what to rent, how to prepare the space, how to run the machine, and the details that separate a professional-grade job from one that wastes money.

  1. Seal all air leaks before blowing. Walk your attic with a flashlight and identify gaps around penetrations: where electrical wires enter, plumbing vent stacks, exhaust fans, and recessed lights. Seal these with expanding foam or caulk. Pay special attention to the tops of interior walls—these are thermal bridges and the most common leak point. This step takes 1-2 hours but saves energy loss and prevents wind-washing of the insulation.
  2. Check local code for insulation depth. Call your local building department or check their website for the required R-value for your climate zone. R-30 to R-49 is typical for most of the continental US, but northern climates demand R-60 or higher. Write down the target depth in inches for cellulose (typically 1 inch = R-3.6) or fiberglass (1 inch = R-2.7). You'll need this number to set the machine's blower gate.
  3. Rent a blower machine and buy insulation. Call a home improvement rental center and reserve a pneumatic insulation blower for 24 hours. Bring the machine home and leave the hopper outside. Order cellulose or fiberglass bulk insulation in bags from a building supply—most places deliver to your home. Cellulose is denser and settles less; fiberglass is cheaper but requires more initial depth. Budget 2-3 bags per 100 sq ft for typical depths.
  4. Lay out drop cloths and mark your depth. Spread plastic sheeting or heavy kraft paper across any attic storage, HVAC ducts, or fixtures you want to protect. Use a measuring stick (a straight board marked with paint stripes at your target depth) to gauge insulation as you blow. Lean this against the wall as a visual reference—you'll glance at it constantly to keep the blower height consistent.
  5. Load the hopper and test the flow. Have a helper start loading insulation bags into the hopper while you go inside and position the hose. Run the machine for 10 seconds to clear the line and feel the air pressure. Check that material is coming out smoothly and not clogging. If it clogs, pull out the hose, check for obstructions, and reload. Once flow is steady, begin blowing.
  6. Blow in passes, working from the far end back. Start at the far corner of the attic, away from the hose entry point. Hold the hose nozzle 8-12 inches above the floor joists and move it in slow, overlapping passes. Work methodically toward the entry point, building up to your target depth. Don't rush—let the material settle for a few seconds between passes. Stop frequently and check your measuring stick against the material level. The surface should look even and level.
  7. Leave air chases clear and finish edges. Do not cover intake soffit vents, attic exhaust vents, or any active ventilation. Mark these areas with tape before you start, and leave a 1-inch clearance around them. Once the main attic is done, use a hand or handheld shovel to feather insulation around edges and under eaves, keeping soffit vents open. Unload any remaining material from the hopper and disconnect the hose.
  8. Return the machine and inspect your work. Back the rented blower out of the attic, wrap the hose, and haul it back to the rental center within 24 hours. Return to the attic in daylight and inspect: insulation should be level, no gaps above top plates, and all soffit vents clearly visible and unblocked. If you spot low spots, you can add cellulose by hand in a bag or two—it's not pretty, but it fills gaps. Take photos for your insulation contractor if you plan to resell the home.