How to Insulate an Attic: The Ultimate Guide

homeowner continuing the process of how to insulate an attic with blown in insulation

How to Insulate an Attic: The Ultimate Guide

As much as 25% of your home’s heat could be escaping through your poorly insulated attic. Just as importantly, an improperly insulated attic can lead to ice dams, which eventually cause expensive leaks and dangerous structural damage to your home.

Calling in a professional to insulate your attic could quickly get costly, but protecting your home and trimming your energy bill by up to 30% is worth making a change. With the right tools and a little patience, insulating your attic is a job you can take care of yourself. This guide will show you how to insulate an attic safely and effectively.

7 Things You Need To Know About How to Insulate an Attic

Attic insulation is a job that can be completed without professional assistance. However, it’s not a project you should begin without the proper instructions, safety measures, and equipment. This complete guide to attic insulation includes:

  1. The difference between insulating a finished vs. unfinished attic
  2. Proper safety techniques and tools
  3. Supplies you’ll need to complete your attic insulation project
  4. How to know the amount of insulation you need
  5. Getting started with the proper preparation of your attic space
  6. Our step by step guide to how to insulate your attic if it’s unfinished
  7. Our step by step guide to insulating your finished attic for living or storage space

 

One Key Consideration for How to Insulate an Attic: Is the Attic Finished or Unfinished?

The way you intend to use your attic space is an important factor in determining everything about your insulation project. The purpose of insulation in your unfinished attic is to keep heat in the rooms beneath the attic. On the other hand, if you intend to use your attic space for a living area or storage, allowing your home’s heat into your attic space is a necessity.

An unfinished attic is properly insulated by placing adequate insulation between and over the floor joists to seal off the area from the living space below. But a finished attic is different. A finished attic is correctly insulated by between ceiling rafters and the studs of exterior walls to prevent heat from escaping through the roof and outer walls of your home.

Different products and techniques may be used for each job. Our step by step guides for how to insulate an attic if it’s going to be finished or unfinished are below. No matter which job you take on, remember to use the proper safety tools and procedures during any building project.

Vital Safety Techniques Are Part of How to Insulate an Attic Correctly

There are a variety of dangers involved during any home renovation project. Taking the proper safety measures and knowing the whole process of how to insulate an attic will help you avoid potential injuries while insulating your attic. If you don’t take the right safety measures, insulating attic spaces could lead to a nasty fall, injuries from various tools, or skin, eye, and even lung issues related to improper handling of insulation products.

Here’s what you need to do to stay safe while insulating attic space in your home.

  • Protect yourself against insulation fibers. Wear goggles, work gloves, long sleeves and pants, and a dust mask rated for use with insulation.
  • Avoid bump and trip injuries. Use battery-powered lanterns, clip-on workshop lights, or headlamps and flashlights to illuminate the work area.
  • Prevent serious injury from dangerous falls. Place wide boards or plyboard that spans at least three floor joists to create a movable walking platform
SAFETY TIP

It’s important to remember that the “floor” of your attic is actually designed to support the ceiling below. Stepping on any area in between the joists without placing additional support while insulating attic spaces could lead to you crashing through your ceiling into the room below.

 

Preparation and Supplies

Before getting started, you want to be sure you have all the necessary supplies and tools on hand.  Stopping during application for a trip to your local hardware store might not be an option. The tools you require will depend on the type of insulation you choose and the structure of your attic. The type you choose will impact the total attic insulation cost, but it’s important to get the type that best fits within the space and creates the appropriate degree of insulation. The different types also require different procedures for how to insulate an attic.

Types of Insulation

  • Loose-fill Insulation: This fiberglass or cellulose insulation is made up of loose particles like the name implies. It requires a machine (which you can rent) for installation. Some homeowners prefer loose-fill insulation because it easily fills nooks and crannies and can be applied without having to climb all through the attic.
  • Batt and Blanket Insulation: This is the most popular insulation for DIY homeowners learning how to insulate an attic for the first time. Made of fiberglass, mineral, or rock wool, it already has a vapor barrier attached and is designed to fit between joists or wall studs. Blanket insulation can be easily cut with a utility knife to fit into smaller areas and is laid by hand.
  • Sprayed Foam Polyurethane: Spray-on insulation is applied with a machine and often requires professional installation, so we don’t discuss how to insulate an attic with this material. Spray-on insulation is typically used during home construction on walls and ceilings for attics that will be finished for usable space.

Additional Supplies

  • Safety supplies (noted above)
  • Machine rental for loose-fill insulation
  • Vapor barrier (if you’re applying loose-fill insulation where all old insulation has been removed)
  • Utility knife
  • Spray sealant or caulk to fill gaps
  • Metal flashing if your home has a chimney

 

How Much Insulation Do I Need to Insulate My Attic?

An important part of knowing how to insulate an attic is knowing how much insulation the space should have. Insulation thickness requirements vary by climate. Any undamaged insulation you already have in your attic will contribute to the complete attic insulation R-value after the job is finished.

What Is R-Value?

Insulation is measured by thermal resistance, or its R-value. The attic insulation R-value is determined by the materials used to create it, the thickness of the material, and its density. Simply put, the higher the attic insulation R-value, the more effective your insulation will be. Typically, layering insulation increases the attic insulation R-value. However, since loose-fill insulation compresses under its own weight, the R-value is harder to increase.

Determining the Amount of Insulation to Purchase

To decide how much insulation you need, first consider your climate. Hot climates require a minimum rating of R-30, but temperate climates should have R-38. If you live in a cold climate, then you need a minimum rating of R-49. After you’ve figured out your desired R-value, measure the square footage of your attic. Before calculating the amount of insulation you need, it’s important to check the quality of your current insulation. Remove any insulation that is compressed, water-stained or moldy. 

To calculate the R-value of your existing insulation, use a tape measure to measure the depth between joists in inches. Each type of insulation is a little different. Learn the type of insulation you have by its appearance and multiply your initial measurement by your insulation type’s corresponding number:

  • Fiberglass loose-fill: (Appearance — loose filling that is white, yellow, or pink) Multiply the measurement you took by 2.5 to determine your current R-value. 
  • Rock wool: (Appearance — dark grey to nearly white with black flecks) Multiply your measurement by 2.8 for your current R-value.
  • Cellulose: (Appearance — small grey fibers or flat pieces) Multiply your measurement by 3.7 for your current R-value.
  • Fiberglass batting: (Appearance — blankets of yellow, white, or pink material with paper or foil backing) Multiply by 3.2 for the current R-value.

If you’re working with loose-fill, use the information on the label to determine how many bags you’ll need. For rolls of blanket insulation, you’ll determine the number of rolls you need by the length and width of the product you choose. Always buy an extra bag or roll of insulation to avoid running out mid-project.

PRO TIP

If your home was built before 1990, and your current insulation looks grainy, feels loose, and has shiny flecks, it may contain asbestos. This type of insulation should only be removed by a professional.

 

How to Insulate an Attic: Getting Started

To properly insulate your attic, it’s important to prepare the space the right way. Take these steps to get the most out of your attic insulation.

  1. Repair any roof leaks before installing new insulation to prevent water damage.
  2. Create a safety area (by building a small box) around exposed light fixtures to prevent fire hazards. Insulation shouldn’t directly touch any type of electrical fixture or component.
  3. If your home vents exhaust into the attic space, take the time to direct those vapors outdoors. This will help avoid exposing your new insulation to moisture.
  4. Determine the location of your roof’s soffits, or openings at the edges of your roof, which provide natural airflow. Keep these from becoming blocked by affixing plastic or foam to the underside of the roof near the eaves. This step also prevents ice dams from forming on your roof during the winter.
  5. Remove any boxes or items on the floor. Shelving or other attic storage solutions can be used after the project is complete. Then you can store out-of-season items without damaging your insulation.
  6. Fill gaps and drafty spaces with caulk or foam sealant. Common gaps include the areas around attic windows, pipes, wires, exhaust fans, and ducts. Use metal flashing for gaps around chimneys and flues.

 

A Step by Step Guide of How to Insulate an Attic That Is Unfinished

man installing batt insulation

Installing sufficient insulation on the floor of your unfinished attic is the most cost-effective way to insulate your attic. This method will provide a barrier to stop heat from escaping past your ceilings. Also, most homes already have some amount of insulation between the attic and the rest of the home, so it’s easy to supplement the existing insulation with the right amount.

Follow these steps for insulating your unfinished attic:

1. Put a movable platform in place.

Use planks or plyboard to form a safe walking space. The platform should span across at least three floor joists for stability. Never step between the joists in your attic without a safe platform to bear your weight.

2. Provide a moisture barrier.

Note: Skip this step if you’re adding to existing insulation.

If your attic doesn’t have insulation or you removed all of the existing insulation, you will need a moisture barrier between the warm air in your house and the cooler air in the attic. Most builders or homeowners use polyethylene sheeting beneath loose-fill insulation.

Blanket insulation typically has a foil or paper backing to block moisture. After you apply the first layer, no other barrier should be between layers of insulation. In fact, moisture is likely to build between these layers if the barrier stays in place. As you’re installing blanket insulation, pull away any excess backing.

3. Insulate the hatch door.

Blanket insulation is the easiest material for this task. Cut two layers of blanket insulation to form a thick pad. Staple the pad to the hatch edges to keep it in place. Also, affix weather stripping around the hatch door for a tight seal.

4. Set up the blower (for loose-fill insulation only).

When you’re installing loose-fill insulation, work with a partner. Place the blower machine outside, close to an attic window or vent access, and snake the attached hose into the attic. Wrap hose couplers with duct tape after attaching to avoid couplers vibrating loose during the process. 

Your assistant will crumble the loose insulation into the hopper while you control the hose inside the attic. This method helps avoid blockages in the hose. Before you start work, create a barrier around the hatch so the material can’t escape as you work. Also, mark several trusses at the desired fill level for easier visibility as you work.

PRO TIP

The machine is too loud to allow communication between partners. So have another means of communication available, like phones or walkie talkies.

5. Start along the wall furthest from the door or hatch.

No matter what type of insulation you use, work your way backward to avoid trapping yourself in a corner. When you’re using blanket insulation, measure and cut pieces, and then layer them between the joists. Keep going until you have layered the insulation deep enough to cover the tops of the joists. If you’re using loose-fill insulation, push the hose out toward the eaves and fill those areas first.

Also, fill tight spots early to avoid leaving gaps. To do so, cut blanket insulation to fit securely into the spaces. But be careful; cramming the material into tight corners can cause air pockets to form. When you’re using loose-fill insulation, attach a length of PVC pipe to the end of the hose with duct tape to get into those hard-to-reach areas.

6. Use all of your insulation.

Even if it looks like you’ve reached your desired level, continue to apply insulation until you’ve reached your target R-value. Insulation compresses as it settles.

Ensure your blanket insulation covers the tops of all of the ceiling joists to stop heat from escaping and to provide the depth necessary to make up for settling over time. Never top lightweight insulation with heavier material (like cotton over fiberglass) because the lower layer will become compressed. Edges that meet should be fitted snugly together, but not tight enough to compress or bunch up the insulation.

Blow in loose-fill insulation evenly until you reach your measurement lines. Continue adding insulation past the guidelines until you’ve used the number of bags required to reach the calculated R-value. You might need to use a rake to help level loose-fill insulation.

Additional Tips for How to Insulate an Attic

  • When you’re using loose-fill insulation, wear a long-sleeved shirt. Taping your work gloves to the edges of the sleeves can help protect your skin from fibers.
  • Adding new layers of blanket insulation perpendicular to the old layers can help eliminate gaps.
  • When controlling the hose for loose-fill insulation, make small movements. This will help avoid stirring up additional dust and improves visibility.
  • If you see gaps between the edges of the blanket insulation, cut thin strips to fill them.
  • Shower immediately after stopping for the day and launder clothes after one wearing.

 

Step by Step Guide to Insulating Your Finished Attic

installing drywall in an insulated, finished attic

Creating a finished attic space is a bigger, more expensive project, but the payoff is additional living space in your home.  You can still expect to reap the same energy savings, as well. Take these steps to insulate your attic before finishing a complete room project.

1. Assess the whole project, not just the requirements of how to insulate an attic.

If your attic has never been used for living space, you may need to make important structural changes to ensure the space is safe for its intended purpose. For example, since the joists in an unfinished attic exist to support the ceiling below, they may not be sturdy enough to support a floor. Your roof will also require a different ventilation technique to avoid ice dams. Your finished attic insulation project will likely fall into one of these categories:

  1. Adding insulation to an already finished space, or
  2. Constructing knee walls and a ceiling that do not follow the attic’s sloped roof shape, or
  3. Insulating the attic space in its entirety.

2. Choose the type of insulation you’ll use.

Choose the insulation that will provide the proper R-value while maximizing as much space as you can. Dense blanket (batt) insulation can provide a sufficient barrier without excess thickness. Rigid foam sheeting is another great option, but it may be more difficult to get into attic spaces. If you’re adding insulation behind existing walls. blowing insulation behind knee walls may provide a simpler solution.

3. Ensure the floor is sturdy.

Before beginning work on an unfinished attic space, inspect the joists for stability. Even if you use your attic for storage, the space might not support the weight of a room. If the room already has plyboard or some other type of flooring, remove a portion to examine the joists below.  Unfinished attic joists are usually two-by-sixes or even two-by-fours. Your joists should be two-by-eights — or even larger — and the builder should have spaced them no more than 16 inches apart (measured from the center of one joist to the center of the next).

Bringing your floor up to code will require a building permit. Still, it’s a job that can be accomplished by a professional or a homeowner with the right tools and knowledge. Your joists may have one of these reinforcement methods:

  • Bridging: Add perpendicular members to support a system that is almost up to code.
  • Sistered joists: Attach additional joists directly to existing joists to add support.
  • Addition of LVLs: Laminated veneer lumber is strong for its size. You can add it between existing joists. 
  • Addition of I-joists: These additional joists each look like a capital letter I. Add them above or alongside existing joists.

4. Provide proper ventilation.

If you’re working in a previously finished space, you likely already have ventilation installed. So be sure you don’t cover the vents while installing additional insulation. If you intend to use the entire sloped attic space, then you will need to install air chutes that run from the soffits to the ridge of the roof within the rafter bay. If you’re installing insulation behind knee walls, soffit vents can be installed.

5. Create your living space.

If you’re using the entire space without adding perpendicular knee walls or a flat ceiling, apply insulation along the rafters before installing drywall or other approved materials.

To work within an already finished space, you’ll likely have to remove drywall from existing knee walls to install more insulation. Adding insulation above an existing ceiling might also require the assistance of a professional. If the existing wall insulation doesn’t have damage, then add new insulation to reach your desired R-value.

If you’re building a traditional room inside your attic space, then create the walls and flat ceiling frame according to your local building requirements. Install baffles, or protective barriers, in spaces where insulation will have to go between the roof rafters for proper ventilation. Also, apply insulation to the flat ceiling and new knee walls to insulate the new living space.

If you intend to use the space outside of the knee walls for storage, you might be interested in temperature control for your personal possessions. In this case, you can apply insulation along the rafters from the room’s ceiling all the way to the floor. 

6. Finish the space.

After applying insulation, complete the internal walls with drywall or other properly coded and fire-resistant building materials. Then add your desired flooring or carpet. If you will use the space every day, you may also want to consider a new stairwell or ladder for more efficient entry.

You may not have the funds to hire a professional, but you can still reap the benefits of adding insulation to your attic if you learn how to insulate an attic on your own. No matter why you decide to insulate your attic, it will help you and your family stay warmer in the winter and cooler in the summer. You’ll also likely notice a difference in your energy bills and add value to your home. Taking care of your attic insulation project may seem like a big hurdle, but the payoff is well worth the time and effort.

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