Installing Attic Insulation

Safety Tip

Improving your home is more satisfying when you stay healthy enough to enjoy it.

You’re Here: Home » Home Insulation  »  Insulation Projects  »  By Room  »  Attic

Attic Insulation

The attic is one of the largest sources of potential heat loss in a home and often one of the most neglected areas when it comes to insulation, especially in older homes. That's why adequate insulation is so important. Without proper attic insulation, your energy bills could be significantly higher. Whether your attic is and will remain unfinished, be used for storage, or be finished for use as living space, make sure that it is properly insulated with the right amount and kind of insulation.

If your attic is unfinished and you're insulating it for the first time, you will install insulation in the floor joists. If you're building a new home, install ceiling insulation up from underneath, before you put in drywall.

You should use faced insulation when a vapor retarder is needed. However, only unfaced insulation should be used near chimneys and flues.

You can also insulate your unfinished attic with blow-in insulation. Blow-in insulation can be installed by a professional contractor, or you can do it yourself. You can rent the necessary equipment from many home centers and rental centers.

How much attic insulation do I need?

How to Insulate Your Unfinished Attic

  1. If you're installing insulation in an existing attic, lay plywood or planks on top of the floor joists temporarily so that you can move around the attic easily and avoid accidentally stepping through the finished ceiling below.
  2. Staple vent chutes over the eaves to ensure proper ventilation.
  3. Start installing insulation from the outside and work toward the center. Gently press the insulation between the joists. When installing faced batts, place them with the vapor retarder facing down toward the warm-in-winter side, unless your local building code specifies otherwise. (Make sure that Kraft-paper facing will come in contact with drywall when it is installed.) At the end of each joist run, make sure the insulation covers the top plate of the outside wall.

    If you're installing faced batts from underneath, hold the insulation up with one hand while stapling the flanges to the side or face of the joist every 6" - 8" with the other hand. Leave a little extra on each end to cover the top plate of the outside wall.

  4. Expand the insulation to its full thickness in the joist cavity to extend over the top of the framing or trusses to insure complete coverage. Avoid compressing the insulation material, because compression will reduce its R-value.
  5. Lay the insulation in long runs first and use leftovers for shorter spaces. Butt insulation tightly at joints for a continuous resistance to heat flow.

Insulating Your Unfinished Attic with Blow-in Insulation

Blow-in insulation (also called loose fill or blowing wool insulation) is ideal for unfinished attics and attics with hard-to-reach areas. You can rent insulation blowing machines at many home improvement and equipment rental centers, or you may choose to hire a contractor to professionally install loose fill in your attic.

Like batts and rolls, blow-in insulation is also specified by R-value. It is a calculation of quantity of materials and rate of blowing needed to reach a desired density and height of material and cover the entire space. To achieve the desired R-value, it will be important to follow package labeling. The minimum number of bags per 1,000 square feet is based upon the net area of the space to be insulated.

Blow-in insulation is highly compressed in the bag. The blowing machine is designed to open up the insulation material, fluff it, and then blow it out through the hose at the rate you set to achieve the specified coverage and R-value.

A useful guide for installing the proper amount of blow-in insulation is to mentally divide the space into four equal parts. Then you can figure how many bags should go into each quarter of the space. For example, if you have 24 bags of insulation, you would blow six bags into each of the quadrants.

How to Install Blow-in Insulation

  1. Remove any objects from the attic that might interfere with the proper application of the insulation.
  2. Staple vent chutes over the eaves to ensure proper ventilation.
  3. Place one or more attic rulers in each quadrant of the attic space. This will help you know when you have achieved the correct depth of insulation.
  4. Load the blowing machine hopper with insulation. The hopper should be kept nearly full so the insulation flow is smooth and even.
  5. Hlid the hose parallel to the floor with the insulation falling 10 - 12 feet away. Begin at the far wall and work toward the center. Always blow in the direction of the joists. Be careful to step only on floor joists, or else you might accidentally put your foot through the finished ceiling below.

    Fill three or four joist cavities by moving the hose to the right and left. Where possible, back away from the work to avoid packing the insulation. Be sure to get insulation to the top of the walls and low places. Don't cover eave vents.

    Avoid using your hand as a baffle to direct the insulation as it exits the hose. Do this only when necessary to avoid packing.

    Keep the hose close to the floor where insulation must go under obstructions like cross bracing and wiring. Insulation must be blown on both sides of these kinds of obstructions. If an obstruction has caused a low spot to occur, fill in the area.

  6. Check the thickness of the insulation, and check that you have used the correct number of bags per 1,000 sq. ft.
  7. Cover any cavities, drops and scuttles with batts.

Insulating Your Unfinished Attic - Adding More Insulation

Over the years, some insulation can become compacted and lose efficiency. If that's the case in your attic, you'll want to add a layer of insulation.

  1. If necessary, staple vent chutes over the eaves to ensure proper ventilation.
  2. If the joist cavities are only partially filled with insulation, lay additional insulation to the top of the cavities.
  3. Lay new insulation at a right angle to the existing insulation and resting on top of the floor joists.
  4. Avoid compressing the insulation material, because compression will reduce its R-value. Butt adjacent pieces of insulation tightly together for a continuous retarder to heat flow.
  5. As an alternative, you may want to hire a contractor to install additional blow-in insulation in your unfinished attic.
  6. Insulation used in attics should not include a vapor retarder.

How much attic insulation do I need?

Insulating Your Finished Attic

A finished attic is an excellent way to expand your living space with an additional bedroom, home office, game room, etc. A finished attic will require complete insulation just like any other room in your house, including the floor, ceiling, interior walls, exterior walls and knee walls. For instructions on how to properly insulate these areas of your home, click on Application Surface and select the appropriate links.

Related Products

ComfortTherm® Batts and Rolls


ComfortTherm® insulation is a lightweight, thermal and acoustical insulation made of long, resilient glass fibers bonded with an acrylic thermosetting Formaldehyde-free™ binder.

Unfaced Batts and Rolls


JM's Unfaced Insulation is a lightweight thermal and acoustical fiber glass insulation made of long, resilient glass fibers bonded with an acrylic thermosetting resin made without formaldehyde.

Attic Protector® Loose-Fill Fiber Glass Insulation


Johns Manville's Attic Protector® loose-fill fiber glass insulation is made for open attics to fill nonconforming spaces and hard-to-reach areas like corners, edges and around framing.

Climate Pro® Loose-Fill Fiber Glass Insulation


Johns Manville Climate Pro® loose-fill fiber glass insulation is made for installation in open attics to fill hard-to-reach areas like corners, edges and around framing.

Copyright ©2014, Johns Manville, Inc. All Rights Reserved. Global Sites | SpecJM.com | Site Map | News Archives
Industry Resources | Privacy Policy | Legal Notices
Product & Sales Information: (800) 654-3103