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How to Insulate an Attic

Insulating your attic is one of the best ways of lowering energy bills and making your home greener. The best thing is the attic is one of the easiest places to insulate. It is thus one of the best places to start when you are making weatherizing changes for all seasons. Heating and cooling costs make up 50 to 70 percent of the energy used in an average home. In most cases, air escaping from the house and air from outside getting in is the leading cause of high heating and cooling costs. Insulating the attic helps prevent air leaks. So, where should you start? If you want to learn how to insulate an attic, this guide breaks down all the steps you should take.

Insulating Attic: Where to Begin?

Keeping the house warm in harsh winter weather is expensive. Considering the cost of heating oil and natural gas keeps on rising, the best way to go is to ensure your home has the best insulation. The best place to start is with attic insulation. Even if you install insulation in all other areas and fail to insulate the attic, your heating bill will remain high. According to the Department of Energy, a well-insulated attic can save you between 10 and 50 percent in heating bills. The results are the same for warm climates.

Stop using the attic as a storage area. The cheapest and simplest way to insulate your attic is by insulating the attic floor. If every inch of the floor is covered in plywood, you will not be able to cover every area with insulation. To get started with insulation, you need to pull up the flooring and install insulation on the old.

The best place to begin is by consulting an energy auditor. The expert will help you know how much protection you need and how many inches of insulation you should install. However, if you can’t afford to work with an energy auditor, this guide will be sufficient. It takes a look at all the crucial know-how about attic insulation products, prep work, cost and installation.

What is the Cost of Attic Insulation?

Before going any further, it is good to get familiar with the cost of complete attic insulation. Home Advisor estimates it will cost you between $1,700 and $2,100. There are several factors that impact the cost. They include the following:

  • Type of material used in insulation
  • Size of the attic
  • Labor costs

While it is possible to do the work yourself, if you will be insulating around cables or electrical boxes, you will need the help of an electrician. You don’t want to encounter an electrical fault that leads to expensive damage, such as fire outbreaks.

How to Choose the Right Type of Insulation

Now that you understand why attic insulation is important and how much it will roughly cost, the next step is to choose the right insulation material. If your target is DIY attic insulation, then you will have two options: loose fill or batt. Both types of insulation can be added to any uninsulated attic or layered over existing material. When you know which type will be ideal for you, you need to consider the material options and the costs. Make sure you read the labels to understand the specifications of the product you are about to choose.

  1. Loose Fill

These insulation materials come packaged in bags. During installation, they are blown into the target area to the desired depth. Special machinery is needed to correctly install loose fill. The fill can also be poured and then spread manually. This option is, however, labour-intensive and doesn’t yield great results.

Loose fill is ideal for:

  • Attics that have nonstandard or irregular joist spacing
  • Attics with so many obstructions that you have to work around
  • Attics with old insulation that requires to be topped. This is preferred because this insulation fills the joints and gaps.
  • Attics with low clearance. If there is limited headroom to permit the installation of other types of insulation, loose fill will be great.
  • DIYers that want to be done with the insulation work fast and can operate special power equipment

There are three options when it comes to loose fill:


  • Fiberglass has an R-value of 2.2 to 2.7 per inch
  • They are made using recycled sand or glass, which is melted and then spun into fibers
  • It is lightweight than both cellulose and fiberglass rockwool. It settles more than both of those materials. You have to install a thicker layer to get the right protection.


  • This has an R-value of 3.2 to 3.8 per inch
  • It is made using fibers from post-consumer paper, which is treated for fire and insect resistance
  • Cellulose is the most common type of blown-in insulation material. It can, however, grow mould or rot when exposed to moisture.


  • This has an R-value per inch of 3.0 to 3.3
  • It is made using fivers from recycled slag or rock from blast furnaces
  • It offers natural fire resistance. It is more expensive than other loose-fill materials.
  • 2. Batts
  • This is a flexible material that comes in rolls and in varying thicknesses and standard widths. They are usually 16 inches and 24 inches, a size perfect for fitting between studs or joists. They are available with or without a paper or foil facing which serves as a vapour barrier. During installation, you add one or several layers to achieve the desired insulation level.

    Batts are perfect for:

    • Attics that have standard joist spacing; more so those without any insulation
    • Attics that have fewer obstructions
    • Attics that have enough headroom to allow easy maneuvering during installation
    • DIYers that don’t mind cutting the insulation material to fit around obstructions

    There are four options available:


    • This has an R-value per inch of 2.9 to 4.3
    • It is made using recycled sand or glass that has been melted and spun into fibers
    • These are quite common and inexpensive. The drawback is fibers can easily cause skin and lung irritation. When compared with other materials, fiberglass is less effective in blocking airflow.


    • R-Value of 3.7 to 3.8 per inch
    • It is made using fibers from recycled post-consumer paper, which has been treated for fire and insect resistance
    • It doesn’t irritate the lungs and skin. There are fewer manufacturers creating cellulose insulation.


    • It has an R-value of 3.0 to 3.3 per inch
    • It is created using fibers from rock or recycled slag from a blast furnace
    • The material is fire-resistant, naturally. It is, however, a more expensive option.


    • Cotton insulation has an R-value of 3.7 to 3.8 per inch
    • It is manufactured using recycled denim cloth
    • It is effective in blocking airflow and also helps with soundproofing. The material is quite expensive.

    What’s the Recommended R-Value for Attic Insulation in Canada?

    The ideal R-value for attic insulation in Canada will depend on the location of your home and the climate zone it is in. The Department of Energy offers minimum R-value recommendations for unfinished and unconditioned attics. For a hot climate, the recommended minimum R-value is R-30, while that for a cold climate is R-49.

    How Much Attic Insulation Do You Need?

    To get the best insulation results, you need to know  how much attic insulation is necessary for your project. To do this, you have to measure the square footage of your attic. If you plan on using loose fill, make sure you read the labels. The loose fill bag includes the required depths for various R-values. The bag also provides information on the number of bags you will need to cover 1,000 square feet at various depths.

    If you went the rolls or batts way, you would have to calculate the number depending on the length and width of the product you are using. To be on the safe side, you have to order an extra roll or bag. Doing so will keep you from running out during installation.

    How to Prepare Attic for Blown in Insulation

    The first thing you have to do when getting ready for attic insulation is to seal air leaks. Gaps in the attic or between the floors will be cooled or heated if air escapes. Air leaks will make your insulation ineffective. You need to start by identifying the main air leaks. Here are a few tips to help fix the draft-prone areas.

    • Area around the windows

    A lot of air leaks in this area. You should use minimally-expanding spray foam to seal the gaps.

    • Areas around wires, pipes, ducts and exhaust fans

    You can seal any gap that is ¼ of an inch or smaller using a fire-blocking caulk. Larger gaps can be sealed using fire-blocking spray foam.

    • Around the flues and chimneys

    To seal these areas, you need metal flashing, which has to be sealed with high-temperature caulk. Furnace cement will also get the job done.

    What to Do Before Insulating Your Attic

    To ensure your insulation lasts for years, there are a few more steps you have to take when preparing your attic. They include the following:

    • Fixing roof leaks

    Water will damage your insulation. When moisture is introduced to the insulation, mildew and mould will grow. This will eventually ruin the pockets that trap air, thus compromising insulation. Always check for water stains on the roof or mouldy spots in the attic. Existing insulation will also help you know if there have been water leaks.

    • Box out the light fixtures

    Unless you went for rockwool or fixtures that are rated safe for contact with insulation materials, you must not allow the material to cover or touch light fixtures. This is because allowing the light fixtures to touch the insulation can result in a fire hazard. To create a safety gap, consider installing hardware cloth, scrap plywood or metal flashing. The safety gap should be used at least 3 inches around the light fixtures.

    • Direct vents and exhaust fans to the exterior

    It is good to note that it is against building code to vent exhausts to an attic. Even so, many homes have escaped with this shortcut. Consider correcting this issue to prevent humid exhaust air from being trapped in the insulation and eventually ruining it.

    Wear Protective Gear When You Install Attic Insulation

    Fiberglass insulation materials are known to cause lung and skin irritation. While the level of irritation they cause has lessened over the years, it is still there and can affect people differently. Blown in insulation can also get in the ears, eyes, nose and mouth. Therefore, before you start installing attic insulation, you must always protect yourself.

    The first thing you must do is wear a dust mask, work gloves, a long-sleeve shirt, long pants and goggles. Doing so will protect your eyes, skin and lungs from the fibers.

    Another important thing to do is never to stand on the joists. If you lose your balance, you can crash through the ceiling. It is always better to use a plywood board or several sturdy, wide boards to stand on. Move these boards as you work. The sturdy boards should span about three joists in order to have sufficient stability.

    Third, you need to make sure the work site is well illuminated. This is more so when it comes to the corners. You need a battery-operated lantern or a clip-on workshop light. Keeping the work site well lit will keep you from getting in an accident as well as ensure you don’t miss any spot when installing the insulation.

    Ensure there is Sufficient Airflow in the Attic

    As you learn how to insulate an attic, it is paramount that you know how to preserve the airflow in the attic. Do not cover the soffit vents using loose fill or batts. Doing so will impede airflow in the attic. Keep in mind that airflow from the soffits all the way to the ridge vent is what keeps your roof cool and eliminates ice dams. Insulating this area will block the flow of air. Moreover, your insulation must not touch the underside of the roof. To keep the insulation away from the roof, staple foam baffles or plastic to the sheathing of the roof. Do so near the eaves.

    Don’t Forget About Vapor Barrier

    As aforementioned, water and insulation don’t go well. That is why you must ensure you install the right vapour barrier. While some batts do come with a foil or paper facing, which creates a vapour barrier, there is no harm in installing an additional vapour barrier. Some experts recommend the use of a 6-mil polyethylene sheeting. This should be cut to fit the space between the joists. The seams must also be sealed using foil tape. Doing so will prevent water from getting into the insulation.

    Whether you are using batts or loose fill, you must ensure you install a vapour barrier close to the warm side of the installation. This is where hot and moist air will get in. In cold climates, this is the area facing the interior of the house, while in hot climates, it is the attic’s interior. There are some regions that don’t require the installation of a vapour barrier. It is, however, better to be safe than sorry.


    Attic Insulation Tips and Tricks

    When done correctly, attic insulation is an investment that keeps on giving. Part of getting things done right involves learning the best insulation installation tricks and tips. In general, regardless of the type of material you are working with, there are three tips and tricks you must keep in mind.

    • The first is to always work from the perimeter of your attic towards the hatch or door. Doing so will keep you from trampling over the new insulation.
    • Secondly, you must always cover the top of the ceiling joists to ensure the insulation is deep enough to achieve the desired R-value. Covering the joists also prevents thermal bridging. This is heat loss that occurs through wood framing.
    • Thirdly, shower thoroughly after working with fibers. Irrespective of whether you were installing or removing fiber insulation, you need to shower thoroughly in order to remove the fibers from the skin. The clothes you wore during installation must also be laundered immediately.

    Away from the general tips and tricks, there are a couple more material-specific tips you need to use.

    1. For loose fill

    To prevent the material from escaping to the rest of the house, always fasten the door or hatch. You also need to ensure you install the material at the right depth. To keep track of the depth, you can screw depth guides to the joists across the installation area.

    To achieve the correct R-value, you must read the specifications given on the bag. The information will help you know how much to insulate attic. Use the number of bags the calculations showed you need to insulate an area and never less than the recommended number. If, after reaching the target depth, you still have loose fill left, continue adding the material throughout the space but at an even depth. Do so until all the bags are used.

    To get to the right density, you should always hold the blowing hose parallel to the floor and floor joists. Blow the fill between and over the joists and not across them.

  • 2. For batts
  • Go for un-faced batts when installing the product for the first time and to prevent moisture problems between the old and new layers of insulation. You can either buy the un-faced batts or remove the foil or paper backing from the faced batts.

    The new layer of unfaced batts should be placed perpendicularly to the old one. Doing so helps cover every space in the old layer. For adjoining batts, butt them snugly together but not too tight that you compress them.

    When laying batts, never lay heavier ones over lighter ones. For example, fiberglass is light and must therefore never be laid below cotton insulation which is heavier. Doing so will cause the lighter insulation to be compressed and become less effective.

    If your attic has obstructions, you should always cut the batts in a manner that helps them fit perfectly around the obstructions. Never stuff or cram the insulation around piping, ducts and other obstructions. Doing so will compress the pockets that trap air and thus reduce the efficiency of the insulation.

    The most important thing to do when working with batts is never to leave gaps between the joists and batts or obstructions. Even the smallest of gaps will pave the way for air to escape. Cutting the batts into thin strips will help fit any area without leaving spaces.

    It is better to use a chef’s knife when cutting batts. A large utility knife will help cut through the depth of the material without any problem. Make sure you have a sturdy piece of wood underneath, such as plywood, to use as a cutting surface. To guide your cuts, stand on scrap 24 as a straightedge.

    Protect the Door or Hatch

    The access spots are a leading cause of air leaks. For the attic door or hatch, you must affix rigid foam insulation. Weather-stripping in the perimeter will also reduce air leaks.

    For a ladder or pull-down stair, you need a zippered insulated tent. This will work by keeping the enclosure free of drafts.

    How Much Can I Save by Insulating My Attic?

    Attic insulation limits air movement within the home. The still air that is trapped in an insulated area helps prevent heat from moving from one area to the next. How effective the insulation is in doing this will depend on its thermal resistance. The higher the R-value is, the better the insulation will be in preventing heated or cooled air from moving from place to place.

    When you insulate the attic and crawl spaces properly, the Department of Energy estimates an average saving of 15% on heating and cooling bills. Savings can increase up to 20% in colder parts of the country.

    As you can see, the cost-saving and increased comfort in the house are the two main reasons you should consider getting attic insulation. However, to enjoy the full benefits of insulating your attic, you must ensure it is done properly.