How to Insulate Walls

Installing insulation in your walls during the process of building or renovating a house increases the energy efficiency of the building, which saves money on heating and cooling. Insulation also helps to buffer sound. Whether you want to use spray or fiberglass insulation batting, the proper steps and techniques are easy for the DIYer to learn, so you can do the job properly.

Method 1

Method 1 of 2:

Installing Fiberglass Insulation

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1
Measure the total area of the walls to be insulated. Before you buy fiberglass insulation batting, you need to find out how much you'll need. To do this, you'll need to take measurements of the total area of the individual walls to be insulated, and also the width of the space between the studs.^{[1]XResearch source} Count up the number of wall gaps you have that need insulation and buy insulation batts accordingly.
- For the most part, studs will be built at uniform spacing, and batting is manufactured to fill those gaps. It should be the perfect width. Still, it's a good idea to count up the number of spaces you have and take a measurement to make sure you don't come home with the wrong size.
2
Choose fiberglass insulation batting. The grade of batting will vary, depending on the wall that you’re insulating. There are various grades of insulating batting for different locations in the house, so you'll need a different insulation for interior, exterior, attic or basement walls.^{[2]XResearch source}
- The R-value of the batt measures the thermal resistance, so the higher the R-value, the more effectively the batt insulates.^{[3]XExpert SourceKevin Schlosser
  Home Improvement SpecialistExpert Interview. 19 February 2021.} Typically, for interior walls, R-13 batts are used for 2 x 4 studs and R-19 batts are used for 2 x 6 studs.
  - Note there are two R-value scales; US customary and metric. The US scale is approximately 5.68 times the metric scale, so R-13 in the US is equivalent to R-2.3 elsewhere.
- You'll also need to choose between faced batts, which have a paper "face" on one side that will cover the insulation to the outside, and un-faced batts, which are just the fiberglass.
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3
Consider “greener” alternatives. While fiberglass is actually up to 40 percent recycled material, there’s still a common complaint about the health-risks regarding airborne fibers of spun glass in your living space. Fiberglass is safe and the most inexpensive form of insulation, but it’s certainly not the only kind. You might consider alternatives, like:
- Cotton. Recycled denim is regularly turned into a kind of insulation that's quite effective, and without the microfiber air problems that some people complain about with fiberglass.
- Mineral and sheep wool, cementitious, and cellulose-based insulation's are also common alternatives to fiberglass.
- You need to only use materials that have a thermal resistance rating. Insulating with things like egg crates and other recycled materials is a dangerous practice that can result in a fire.
4
Get other tools necessary to complete the job. To install fiberglass or other insulating strips into your walls, you'll just need a few basic tools and the proper safety equipment. Make sure you've got:
- A staple gun
- Utility knife
- Protective gear (gloves, mask, long sleeves and pants)^{[4]XResearch source}
5
Cut batts to the appropriate height. You should have purchased insulation of the appropriate width, but you'll have to cut it to size for every space you want to fill, in terms of height. Lay the insulation out, then carefully use your utility knife to cut through the face (if you've purchased faced insulation). It's kind of hard to cut through the insulation itself, which has the consistency of tenacious cotton candy, but you can pull it apart once you get it started.
- When you get your insulation home, keep it wrapped up until you're ready to use it. Cutting fiberglass insulation sends lots of little fiberglass particulate up into the air, which can cause allergic reactions and breathing problems. It's also extremely itchy, and can cause rashes in some people with sensitive skin. Never touch fiberglass batting with your bare hands and always wear breathing equipment when handling it.
- If you come into contact with fiberglass insulation, don’t scrub your hands or face with water, which can cause micro-abrasions. Dust yourself off outside and wash your clothes immediately.
When you get it cut, just shove it in to the space, with the face pointing back outward, if you're using it. Try to handle it by the edges as much as possible, to keep the floating particles down. Gently tug each batt outward so it fills the gap entirely.^{[5]XResearch source}
7
Secure the lip of the batting to each stud. Use your staple gun to secure the paper lining to the stud, roughly every 7 inches (17.8 cm). It's helpful to have an assistant hold the insulation in place, if necessary. Staple each piece securely, then move on to the next row.
- If you're looking for sound-dampening, it's a good idea to apply a thin line of caulk between the top plates, at the bottom plate, and around the floor of each batt. This will create a more secure seal that will keep sound from coming through.
8
Apply vapor-retardant poly film over batting for exterior walls. To make external walls extremely insulated, it's common to apply a layer of vapor-retardant film over the insulation, to make it more secure. This will help to maximize the insulating potential of the batting, and you can find this at most home retailers.
- To install, you'll simply pull the film tight over the batting, stapling to the studs every foot or so, with the staple gun. Trim the excess with the utility knife.

Method 2

Method 2 of 2:

Adding Spray Foam Insulation

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1
Make sure you have a suitable space for spray foam. If you want to insulate an area in your crawl space, attic, or basement, spray foam insulation might be appropriate for the job, using a low-pressure sprayer and the proper safety equipment.
- For the most part, roofs and other major renovation jobs require a lot of spray foam to insulate, meaning that it would probably be more cost effective to hire professional insulators with a spray rig, high-pressure applicators, and safety gear.
- Use spray cans of insulation for small jobs, like gaps between windows and doors, around dryer vents, fan outlets, and other plumbing. Spray cans are good for fixing small leaks, but not cost effective for insulating a wall.
2
Get a low-pressure sprayer. Generally, disposable and refillable spray insulation tanks are sold as part of a spray foam insulation kit. It's not cheap, but you'll be able to quickly and easily insulate a small area. Each manufacturer will vary slightly in its
- You'll also need protective equipment. This means you'll need eye protection and a respirator.^{[6]XResearch source} A full work suit would be ideal, but long sleeves and pants will also do in a pinch.
3
Choose between open and closed-cell insulation spray. Closed-cell insulation is rigid and dense, with a higher R-Value than open-cell. Most closed-cell spray is rated around 6.6, with open-cell insulation rated around 3.9. The advantage of open-cell is that it's super-fast and cheap, included in most individual small spray cans of foam.
- In wall-insulation, small holes are usually made in the drywall, into which the sprayer nozzle is inserted to fill the cavity with the spray inside the wall. For this method, open-cell is most often used, especially for ceilings and interior walls. It's sound-proof and used in the same locations as fiberglass. Closed-cell is usually used on external walls.
4
Prepare the area for insulation. Remove exposed nails, debris, and other impediments from the walls to be insulated. Identify drafting areas–seams where you feel air leaking, see daylight, or see a gap. Mark these areas with tape, or a pen to make sure you address them with the insulation.
- It's a good idea to cover nearby furniture or finished flooring with plastic tarp to avoid getting any of the insulation on it. It's difficult to get out.
- It's best to apply spray insulation when the temperature is between 60 and 80 degrees F.
5
Apply the spray from about two feet away. Attach your sprayer to the canister or bucket of insulation and start spraying, as if you were washing a window or car. Don't get too close, but stand a few feet back and spray as evenly as you can, back and forth across the area to be insulated. If you're spraying inside a wall, count to three, then stop and examine your progress to make sure that you aren't over-filling the wall.
- Insulation needs to be kept in a layer no deeper than an inch. Over-applying foam insulation can stress the walls and can also clump up and fall off the surface.
- If you miss, or get insulation somewhere you don't want it, don't panic. Stop and allow the insulation to dry and scrape it off the surface with a putty knife later. Trying to smear it now will make it worse.
- If you need to add multiple layers, because you're spraying an external wall or want extra sound-proofing, wait until the first layer has dried before going back over it as you did before. This will build up the R-Value of the insulation accordingly, and should stick perfectly well.
Spray foam is not a finished surface and will ignite quickly in the event of a fire. After applying, it's common to drywall over the insulated area to finish the job.^{[7]XResearch source}

Expert Q&A

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How do you cut rigid foam insulation?
Lui Colmenares
Handyman
Lui Colmenares is a handyman and licensed home improvement contractor for Mr. Handy NYC based in New York City, New York. Lui is trained and educated as an industrial engineer and specializes in carpentry, painting, and general handyman work such as mounting TVs, doorknob and deadbolt installation, furniture assembly, tile repair, and grouting. Mr. Handy NYC prides itself on quality work performed with speed, skill, and punctuality.
Lui Colmenares
Handyman
Expert Answer
You use a handheld circular saw. One of those smaller ones with a 4-inch blade.
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How do you cut foam or soft insulation?
Lui Colmenares
Handyman
Lui Colmenares is a handyman and licensed home improvement contractor for Mr. Handy NYC based in New York City, New York. Lui is trained and educated as an industrial engineer and specializes in carpentry, painting, and general handyman work such as mounting TVs, doorknob and deadbolt installation, furniture assembly, tile repair, and grouting. Mr. Handy NYC prides itself on quality work performed with speed, skill, and punctuality.
Lui Colmenares
Handyman
Expert Answer
You can cut soft insulation with a utility knife. Foam insulation is typically sprayed into the wall, so you shouldn't need to cut that stuff at all.
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How can I prevent issues with heat transfer when I'm using fiberglass insulation?
Kevin Schlosser
Home Improvement Specialist
Kevin Schlosser is a Home Improvement Specialist and the Owner of Home Tech Handyman Ltd. With over 20 years of experience, Kevin specializes in age-in-place installations, flooring, roofing, and general remodeling handyman services. Kevin holds a blend of construction and in-home technology-related certifications including NAHB Certified Age-in-Place Specialist, CEDIA membership and certifications, and a Certification from the Association of Certified Handyman Professionals. Also, he is in training to receive certifications in Construction, Project Management, and other CEDIA qualified system integrator certifications. He is fully-insured in the state of Colorado.
Kevin Schlosser
Home Improvement Specialist
Expert Answer
You want to make sure you have a tight building envelope when you're installing the insulation. When they leak air, it is known as not having a tight envelope. This is the number one contributor to problems related to heat transfer in the home.
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Tips

If you need to cut the batt, do so from the insulation side (of faced batts).
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As you place batts in the cavities, you may find outlets or plumbing in the way. You will need to cut the batts around those fixtures.
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Inserting all the insulation first and then stapling the batts down all at once is the most efficient installation method.
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Warnings

Do not pull on or stretch the facing paper as you staple the batts. This can cause gaps between the batt and stud on the opposite side.
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Do not install fiberglass insulation without wearing the proper protective gear. Use a dust mask to prevent inhalation of fiberglass and other particles, use goggles to shield your eyes, and wear gloves and a long-sleeved shirt to avert itchiness caused by fiberglass contact on the skin.
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