How to Install Attic Insulation Over Existing? Quick Guide, Tips, Cost & Insulation Needs

You probably already have some insulation in your attic and may want to increase your R-value. Are you wondering whether it is possible to add new attic insulation over existing insulation? It is possible, and you probably should not have to remove your existing layer to get more out of insulating your attic.

By installing insulation in your attic, you will be able to reduce monthly utility billing very easily. Plus it also helps to improve the overall energy efficiency and provide excellent comfort for long years. Moreover, insulation is easy to install and can be finished in just one week.

Right here we will explain to you a quick guide about how you can install attic insulation by following some easy tips. We have also discussed its approximate cost for you.

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Source: Lowes

Calculate Basic Insulation Needs

  • You have to measure how much insulation you are already having. By using a tape measure, it is mandatory to check the depth.
  • Now multiply the number of all inches of your insulation by R-Value per inch. According to the U.S. Department of Energy, fiberglass batts is having an R-value of 3.2 per inch, while loose-fill fiberglass will approximate measure R-2.5 per inch. Rockwool also offers R-2.8, while cellulose made out of old newspaper measures around R-3.7 per inch.
  • After it, you have to perform some basic calculations about how much of the insulation do you require which will be based on your suggested R-values of that area. For instance, in California, the recommended range of attic insulation is around R-30 to R-60.

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Installing Fiberglass Batts over Existing Batt Insulation

  1. Don’t forget to wear gloves and Goggles to fully protect yourself against the handling of fiberglass insulation.
  2. Now cut down the fiberglass batts so you can score it by using a utility knife. Size every single piece so it can get fitted snugly between the floor joists in your attic.
  3. In between the joists, you have to place the batts within the spaces. Do not compress the material together. To achieve the required R-values, you have to add some extra layers.

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Adding Loose Fill Insulation to Existing Loose Fill

  1. First of all, you have to buy a loose-fill insulation blower from any home improvement or hardware store.
  2. Block all the vents inside the attic floor with the help of baffles. Make sure it extends the baffles to almost 4 inches above the required thickness of the insulation which you have planned.
  3. While you are directing any hose or blower, you should add some material inside the Hopper. Now spray down the insulation over the corner sides and perimeter of your attic. This will help you to make your way inside the center.
  4. Spread the whole insulation over the area of the attic floor by using a rake or push broom. Now measure the thickness of your loose-fill material to achieve the desired range of thickness as well as R-value.

Source: Buildings

Major Things Needed

  • Tape measure
  • Safety glasses
  • Gloves
  • Insulation
  • Utility knife
  • Vent baffles
  • Insulation blowing machine
  • Broom or rake

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Step by Step Guide on How to Install Attic Insulation

Before you begin actually installing the insulation, there is some important preparation involved in order to ensure that the insulation is applied properly to prevent hazards and to achieve maximum effectiveness.

Step 1: Install Roof Baffles

In order to preserve the free glide of outdoor air, it is suggested that polystyrene or plastic roof baffles are mounted where the joists meet the rafters. These can be stapled into place.

Step 2: Place Baffles Around Electrical Fixtures

Next, locate baffles around any electrical fixtures (lights, receptacles, etc.), seeing that these may also end up warm while in use. Hold the baffles in one place by way of cross-sectioning the rafters with 2x4s positioned at a 3-inch clearance around the fixture.  Cut the polystyrene board to suit around the fixture and inside the wooden rectangular you have simply created.

Step 3: Install a Vapor Barrier

If you are putting in insulation with a vapor barrier, make sure it faces the indoors of the house. Another choice for a vapor barrier is to take sheets of plastic and lay them between the ceiling joists.  Then, by using a staple gun, tack them to the side of the joists.

Step 4:  Apply the Insulation

Begin by cutting long strips of fiberglass to measure, and lay them in between the joists. Do no longer bunch or compress the material; this will limit the insulative effect.

If you are no longer planning to put in an attic floor, the second layer of insulation can also be laid at 90º to the first layer. Do not lay a second moisture barrier, as moisture would probably be trapped between the two layers. This second layer of insulation will make it less difficult to acquire the endorsed R-value.

In chillier climates, an R-value of 49 is encouraged for enough attic insulation. In hotter climates, an R-value of 30 is recommended. Fiberglass insulation has an R-value of roughly three per inch of thickness; cellulose has an R-value of roughly 4 per inch, however, it would not preserve its R-value ranking as well as fiberglass.


  • You should never block the attic vents or even the exhaust systems with certain insulation.
  • Try to merely walk on the wall joists of your attic and now space which is in between of it. Otherwise, it can injure you or damage your home as it is not capable enough to support your body weight.


  • To avoid any sort of moisture problem, you should use unfaced batts.
  • If you experience that space in between the joists has been already filled with insulation, then you need to add some insulation over the top of the joists by running new material in a perpendicular direction to the existing batts.

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When do should add new insulation over the existing one?

You can install the new layer if in case the old one is not wet. If in case the existing layer is wet, then it is mandatory to remove it instantly and figure out the source of leakage. Later on, it needs to be identified and fixed. Wet insulation can cause wood rot, structure damage, mold development, or mildew.

You cannot place the faced insulation over the existing attic insulation. If you are having any new rolls or batts, then they should not be having a vapour retarder or face. This face can trap water if it is located on top of the insulation layers or even between them. Face insulation should be positioned in a direction that is against the drywall floor or your attic.

Overall Cost of Attic Insulation

An approximate cost of attic insulation will fall between $1600 to $2200. Few major factors which can affect the cost are:

  • Material and type of insulation
  • Square footage of the attic
  • Contractor or fee of the insulation installer

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Before you plan to install any sort of new layers, it is important to perform a quick and detailed inspection of your attic to get an idea about major insulation factors. You can even figure out if there is any sort of disturbance or wetness by rodents in the attic.

Plus also make sure that you have fully air-sealed the attic before the process of installation to get the best results of high performance from your new layers.

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