Insulating an Attic: Benefits, How-to & Tips

Ever wonder how to lower your energy bill without sweltering in the summer or freezing in the winter? According to the United States Department of Energy, proper insulation and air sealing can achieve energy savings of 10-20%. The estimated savings are even higher for older houses with little to no insulation. 

The best part is that you don’t have to pay an arm and a leg for professional installation. You can insulate an attic yourself. 

Whether you’re an owner-builder looking to install attic insulation for the first time or a homeowner hoping to update old insulation, read on for a step-by-step guide to insulating an attic. 

Benefits of an Insulated Attic

The USDE recommends insulating a home from the foundation to the roof for optimal energy efficiency. Insulating between the attic floor joists helps keep the air distribution in the living space. 

We tend to think of insulation as a way to keep warm, but it also keeps your home cool. In containing air distribution to the living space, attic insulation prevents AC from escaping on hot summer days. 

Attic insulation can also help prevent structural damage caused by ice dams. Ice dams are thick ridges of solid ice that form along eaves. The weight of ice dams can rip off gutters and shingles, making it much easier for water to enter your house. 

Ice dams form when snow meets a roof warmed by interior air. This heat warms the snow, turning it into meltwater which then freezes into an ice dam at the roof’s edge. 

Insulation along the attic floor keeps warm interior air in the living space. Thus, the attic air will stay closer to the exterior roof’s cooler temperature.   

A Good Attic Starts With – Air Sealing

spray foam gun for air sealing

Before you begin installing or upgrading insulation, inspect your attic for air leakage. This inspection should include leaks from the living space as well as from the outside. (And if you’re using your attic for storage, this is the time to remove stored items until you’ve completed your insulation project.) 

A thoroughly sealed attic prevents heated or cooled air from escaping the living space through the attic. This prevention will increase your home’s comfort and energy efficiency; it will also help prevent mold and rot – which are more likely to occur if warm air from the living space enters the colder attic.

Sealing leaks will also prevent contaminants (mouse droppings, mold, fiberglass, and asbestos) from entering the living space. 

Pay particular attention to these areas where leaks and penetrations frequently occur:  

  • Plumbing, Pipes, and Ventilation Systems
  • Chimneys and Flues
  • Windows
  • Bath Exhaust Fans
  • Recessed Can Lights
  • Ceiling Electrical Boxes
  • Electrical Cables and Wires
  • Heating and Cooling Ducts
  • Between Partition Top Plates
  • Between Partition Drywall 

The location and size of the leak will determine how you should seal it, but typically you will need to use spray foam or caulk. 

Check for areas where large volumes of air can escape in addition to the sneaky crevices. And also for unsealed soffits or improperly sealed dropped ceilings. 

This inspection must include the attic hatch. Insulate your attic hatch with rigid foam and weatherstripping.

If you have a walk-up attic rather than a hatch, add a sweep to the bottom of the door and apply weatherstripping around the door’s perimeter.

Keep the area surrounding pull-down ladders draft-free by installing a zippered, insulated tent at this location. 

Want to take this inspection to the next level? Hire a professional to conduct a blower-door test: a diagnostic tool that will identify air leakage you might otherwise miss. If performing a blower test yourself, be prepared with various sealing materials (tape, caulk, spray foam) to address any leaks you discover. 

Although it can be tempting to skip the prep work and jump into the main project, it will be much harder to identify and access air leaks after you have installed insulation.

How to Install Attic Insulation 

If you hire a contractor to insulate your attic, the total cost of their fees and materials will be about $1,700-$2,100 (according to HomeAdvisor). Professional contractors will probably install spray foam or structured panels (costing up to $7 per square foot).

Pro Tip: Don’t sacrifice insulation depth to save money. The cost of hiring a contractor to insulate your roof primarily covers getting the crew and equipment on site. Using 8 inches of cellulose versus 16 inches of cellulose won’t save you much money in the grand scheme of things.

The most common types of insulation for non-professionals are loose fill and batting. These materials cost about $2-$5 per square foot. 

If you want some professional input before you begin insulating, an energy auditor can assess your home’s existing home insulation for a couple hundred dollars. (Your local HVAC contractor, power company, or roofing company should be able to refer an auditor.) 

As you calculate the costs, keep in mind that even a small area of improperly installed insulation can greatly decrease the overall R-value of your attic. When in doubt, hire a professional. But if you’re still determined to insulate your attic yourself, keep reading.

Step 1: Establish Your Insulation Goals

Before you go out and buy any materials, consider why you want to insulate your attic. 

If you are trying to convert your attic into a living space or bonus room, you’ll want to insulate the attic ceiling – between the rafters and wall joists. Doing so will be a bit trickier than installing insulation on the attic floor, so you might want to hire a professional to apply spray foam or rigid foam panels in these areas. 

But if you’re just trying to keep the living space below the attic comfortable, you’ll insulate the attic floor. (Assuming you’re not trying to store temperature-sensitive historical artifacts in your attic, insulating the attic floor will be fine for using your attic as a storage space.)

In either case, you’ll need to determine the minimum R-value for your project. R-value indicates a material’s thermal resistance (in layman’s terms: the material’s ability to prevent heat from moving between two spaces). Measured in per-inch units, R-values range from 2.0 to 8.0. The higher the R-value, the better the insulation. 

The amount of R-value you need depends on the climate zone where your house is located. 

The International Code Council (ICC) updates building codes listed in the International Energy Conservation Code (IECC) every three years. Here are the IECC’s most recent recommendations for residential buildings, updated in 2021:

  • Climate Zone 1: R-30
  • Climate Zones 2 or 3: R-49
  • Climate Zones 4 – 8: R-60

You’ll find the R-value listed on the insulation’s product packaging or product description. 

Step 2: Select Your Materials 

Unless you are a professional builder, you will probably insulate your attic using either loose fill or batts. (Installing spray foam requires professional precision and knowledge of fire safety requirements.) 

The type of attic insulation best-suited to your attic depends on a variety of factors: attic accessibility, durability requirements, desired eco-friendliness, and project budget. But the biggest factor to consider when choosing attic insulation is its R-value. 

The type, thickness, and density of material will determine its R-value. Temperature, aging, and moisture accumulation can negatively impact R-value, so consider those factors before selecting a material. 

Fiberglass batts are popular for DIY insulation because they are cheap and offer straightforward installation. However, it is difficult to install fiberglass batts correctly. Improper batt insulation greatly reduces their effectiveness. 

Blown-in cellulose or fiberglass will provide better insulation as it will conform around nooks, crannies, and other obstacles. 

To determine how much insulation material you need, measure the square footage of your attic. If you’re using batts, multiply the length and width of the batts to determine how much you’ll need. The labels on loose fill bags will list the depth you need to achieve specific R-values as well as the number of square feet the bags will cover at those depths. 

You can purchase insulation materials at most hardware stores. 

Step 3: Prepare Your Attic 

If your attic floor is covered in plywood (which is likely the case if you’re already using the attic for storage), you will need to pull up this flooring before installing new insulation. 

Remember that the surface often referred to as the attic ‘floor’ is actually just floor joists with drywall below. Only step on ceiling joists; do not step on the backside of your drywall ceiling. Even if builders have installed OSB rather than drywall, you still don’t want to step on the ceiling.  

If you need additional stability or movement flexibility, place kneeboards across three or more ceiling joists. 

Use a marker to mark the necessary insulation depth on the attic floor joists.

Step 4: Install Ventilation Baffles & Insulation Dams

After you have prepared your attic, install ventilation baffles and insulation dams. 

Baffles help keep insulation material away from ventilation channels. This pathway allows air to flow into the attic via the soffit vents. If you block the soffit, air will not be able to flow from the soffits to the ridge vents. This airflow is necessary because it helps keep the roof cool, preventing ice dams. 

 Any insulation that touches the roof’s underside also increases the likeliness of ice dams. 

Locate the soffit ventilation. Your baffles should be long enough that, when installed above this soffit, they end above the top of insulation installed on the attic floor. 

Insulation dams act as air barriers between the underside of your ventilation baffles and the top plate of the exterior wall. Also known as soffit dams or wind-washing dams, these dams ensure that the attic insulation covers the wall’s top plate.

Next, install an insulation dam around your attic hatch. Keep in mind that this dam should be higher than the depth of insulation you plan to install. 

Some builders use plywood or OSB as insulation dams, but rigid foam will be the easiest material to install. Use canned spray foam to seal the perimeter of each dam.

Step 5: Install Insulation 

The method of installation will depend on whether you’re using batts or loose fill. 

Installing Batts

installing fiberalls batt insulation in an attic

If you are using batts face with a foil or paper sheeting, place this vapor barrier on the warmest side of your installation to repel hot, most air. In cold climates, place the vapor barrier closest to the house’s interior. In hotter climates, point the vapor barrier toward the attic’s interior. 

Place your batts between floor joists, fitting them close enough to be snug but not so tight that you compress them. Cut to fit batts around any obstacles. Cramming batts reduces their insulation effectiveness. 

Remember, even a small amount of uninsulated space will reduce the insulation’s overall performance. Cut insulation to fill gaps between batts, joists, or other objects. 

Top Tip: Do not install heavier batts over lighter batts. Doing so will compress the lower level, reducing its effectiveness. 

For Loose Fill 

loose fill fiberglass insulation

You can install loose fill by hand, but the best option is to use a blower, which you can rent from most major hardware stores. (You will want to have at least a two-person crew when using this method.)

Place the blower as close as possible to the attic access. Keep in mind that this location might become messy while loading cellulose or fiberglass into the blower. 

Run the blower’s hose into the attic, following the most direct path. Have one person feed loose fill bales into the blower’s hopper. An agitator inside the blower will break up the insulation, after which air will blast the loose fill through the hose.

Another person will operate the hose inside the attic, working from the perimeter toward the access point. Blow the hose between the joists rather than spread the material across the joists.

Insulation depth is not the place to cut corners, so apply liberally and make sure to fill any nooks and crannies. Use every bag you calculated needing, even after reaching your target insulation depth. This will ensure you achieve your desired R-value. 

Once you’ve blown in the insulation, use a rake to even the distribution, creating a smooth, flat bed of loose fill. (Lumpy insulation has a worse R-value average because it allows for more heat flow.) Check that you have filled in loose fill to at least the depth you previously marked. 

Updating Ineffective Insulation 

Whether your attic contains batt or loose fill insulation, updating ineffective insulation is a simple way to make your home more energy-efficient. 

Easily identified by its cotton candy texture and bright pink, yellow, or white color, batt fiberglass insulation becomes discolored or torn as it ages. Torn, damaged, or improperly installed insulation reduces the insulation’s performance. 

If your attic contains damaged batt insulation, upgrade your batt insulation in a few easy steps:

  • Check that batts fit tightly on the ceiling’s drywall and framing edges. 
  • Tighten end joists to prevent further batt separation/tearing. 
  • Fill any gaps or voids with new pieces of insulation. 

Alternatively, if you have improperly installed batts between the floor joists, you can blow in a layer of cellulose insulation on top to fill any open spaces. Filling these gaps will improve the R-value and reduce convection loops that could otherwise degrade the fiberglass batt’s performance. 

It is also possible to increase insulation by adding a layer of new batts on top of the old batts. Bring the old batts flush with the top of the joists. On top of this layer, install a layer of unfaced batts perpendicular to the joists. 

To upgrade loose fill insulation, first install a layer of rigid insulation in the truss bays over the exterior wall plates. This layer will act as a blocker, preventing the insulation from falling into eave soffits while also maintaining channels for roof ventilation. Notch the rigid insulation as needed to fit them as tightly as possible in the truss bays.

Once you’ve made this preparation, you can install new loose fill over the existing insulation. 

A Few Final Tips

A properly insulated attic can help make your summers cooler and your winters cozier. Plus, everyone loves a lower energy bill. 

Follow these tips for a safer and more successful attic insulation project: 

  • Mask Up: Always wear appropriate safety equipment when handling insulation materials, especially fiberglass. This protective gear should include a mask or respirator, safety goggles, gloves, long pants, and a long-sleeved shirt. 
  • Light Up: Attics aren’t known to have much natural lighting, so bring in any additional lighting you need to see clearly. 
  • Stay cool: If you’re working in the summer, remember that heat rises, meaning attics can get pretty hot. Try to work in the morning or evening when the sun isn’t beating on the roof. 
  • Work Smarter: Begin insulating the perimeter of your attic, working toward the entry. The last thing you want to do is force yourself to walk on (and damage) newly installed insulation. 
  • Prevent Fire: In addition to following any safety guidelines provided on the material’s packaging, prevent fires by keeping insulation at least 3-inches away from recessed lighting. 
  • Stay Clear: Remember not to cover soffit vents with insulation. You don’t want to block the airflow necessary to prevent moisture accumulation in your attic. 

Shower thoroughly and wash your clothes at the end of your workday to remove hazardous fibers. 

If you decide to hire a professional to insulate your attic, remember that Trade Regulation requires builders and insulators to provide documentation that they have met the requirements of the Federal R-value Rule. This documentation will provide details about the R-value of the insulation they installed, giving you peace of mind and the benefits of proper insulation. 

References

United States Department of Energy – Link