How To Insulate Walls
One of the most effective renovations you can make to your home is to add insulation to your walls. Many older homes, especially those built before World War 2, don’t have any insulation at all. Installing fiberglass batts requires gutting and drywalling the walls entirely, which is more expensive (and invasive) than most homeowners would like, but there are methods for adding insulation to existing walls.
How do you insulate existing walls? Instead of tearing the drywall down to install fiberglass batt, you can inject loose-fill insulation (either fiberglass, cellulose, or mineral wool), expanding foam insulation, or fiberglass pellets into a hole that is drilled into either the interior or exterior side of the wall and later patched. There are many factors to consider when choosing which option is best.
In order to decide which option is best for your project, let’s take a closer look at what each method entails. Doing so will illuminate the pros and cons of each method and help you make the right choice.
You’ll notice the above chart lists the R value of the different insulation materials. R-value is a measure of how efficiently a two-dimensional barrier, such as a layer of insulation, resists the transfer of heat.
In short, the higher the R value, the more effective the insulation. You can increase the effectiveness of the insulation by adding more layers of the material, but because there is a limited amount of space within the thickness of the wall, using insulation with a higher R value is the best way to increase your home’s insulation.
Insulating Walls with Batts
If you were building a new wall yourself, you’d almost certainly insulate it with batts. Insulation batts come in long rolls that are cut to the standard width between your studs. They come in various thicknesses and can come with one side backed with paper or not, depending on if you need a vapor barrier on not. Though the insulation is typically irritating to your skin, installation is a relatively simple process that only requires basic tools and safety equipment.
For existing walls, however, this option requires a lot more work. To install batts in an existing wall, you need to tear all the trim and drywall off one side of the wall to expose the studs, insulation, and then drywalling, mudding, sanding, and painting the entire wall reinstalling the trim. This method is more of a remodel than just an addition of insulation, and not an option if you want to preserve the walls as they are.
When the space between studs is standard size and unobstructed, installation is as simple as cutting a piece to length and stuffing (and possibly stapling) into place. There are a few complicating factors, but even these are easily worked around:
- If the presence of a door or window results in some openings less than the standard distance apart, the batt can be cut to watch not only the length but also the width of the gap easy enough.
- If there are obstructions between the studs, such as pipes, wires, electrical boxes, or ducts, it can be a bit trickier to ensure there are no spaces left open, which will make the insulation less effective.
Fiberglass, mineral wool, and even cotton batts are among the cheapest insulating materials. Wool batts, which can only be purchased online from Canadian companies, can be a bit pricier. The fact that the studs must be exposed, however, makes this option typically only used for complete remodels.
Insulating Walls with Blow-In Insulation
Instead of tearing open the entire wall, a less invasive method is to blow in insulation through small holes 1 to 2.5 inches in diameter.
Insulation can be blown in from the interior or exterior side of the wall.
- If blowing in from the interior, the hole is cut in the drywall at the top of the cavity, between the studs, and is later patched and repainted.
- Blowing from the exterior requires prying up the siding, drilling through the sheathing, and reinstalling the siding when complete.
Both options are less destructive than a complete gutting.
Insulation is blown into the hole, falls via gravity until the space is filled. Some obstacles could result in less than perfect filling. The loose fill insulation can sometimes leave gaps if the fall is obstructed by pipes, wires, or even cobwebs. If the cavity has protrusions or awkward shapes, they may end up unfilled.
The loose insulation blown in can affect this method’s effectiveness. Blowing in fiberglass may not be as effective as fiberglass batts because the loose fill method may not achieve the same density as the batts. Cellulose, which is about 80 percent ground-up newsprint and 20 percent borate, a mineral added as a fire retardant, is cheaper because it uses less energy to manufacture. It does, however, absorb moisture, which makes it less ideal for wet, windy areas, especially in houses with wood siding.
Having insulation blown in typically costs $1.20 per square foot installed when blown in from the interior side, and $2 per square foot from the exterior side. The materials are only a third of this cost, so it is possible to rent a blower for $70 a day and save money by doing it yourself. Over time, the loose fill insulation can settle, resulting in gaps of open air at the top of your wall.
Insulating Walls with Blow-In Blanket
A company has developed a patented new construction method called Blow-In Blanket (BIB), which uses fiberglass pellets as the loose insulation material. The pellets form a tight, dense, seamless blanket of insulation that is highly effective at stopping air infiltration. It also doesn’t absorb moisture, which prevents the growth of mold and mildew, and the pellets do not settle over time.
Because the BIB process is patented by a single company, it is not widely available, and it is not possible to do it yourself.
Insulating Walls with Injection Foam
Expanding foam insulation is such a versatile and effective option that it is often used whether the studs are exposed or if it needs to be blown in. In either case, the expanding foam is able to force itself into every nook and cranny in the wall space, filling the area completely and forming an air-tight seal.
Using Insulating Foam With Exposed Studs
The best way to install insulation is always when the studs are exposed. It is easier, and you can do the job much more thoroughly.
- When insulating a wall that is open with completely exposed studs, an open-celled polyurethane (or polyicynene) is used, which expands to 100 times in volume in a matter of seconds.
- A cementitious foam, which is applied as a shaving consistency and hardens into a meringue, can be used if you install wire mesh across the studs to contain it.
- It is possible to apply a very thin layer of expanding foam in order to create a tight seal and then fill the cavity with a less expensive fiberglass batt in order to save money on materials.
Blowing in Insulating Foam
When blowing insulating foam into an existing wall, a tamer version is used to avoid cracking the drywall from the quickly expanding foam.
The blown-in open-celled polyicynene expands 60 times its volume, and closed-cell polyurethane expands to 30 times its volume over the span of a few minutes. Including labor, it can be almost twice as expensive to install expanding foam into existing walls than exposed studs.
Some manufacturers offer moderately priced kits for those inclined to do it themselves, but it’s probably best left to the professionals. If not blown in properly, the foam can crack walls as it expands, or leak through and stain floors. Regardless, a common complaint is that because the hardened foam isn’t flexible, gaps can form as the studs expand and contract.
Which Method is Best
The insulation method that is best for your project depends on many factors. If you have exposed studs (or are willing to completely gut the wall), it’s very easy, cheap, and effective to install fiberglass batts yourself. If you’d like an airtight seal, you can spend a bit more to have a professional spray it with expanding foam.
If you want to cause minimal damage to an existing wall, you’ll want to blow in insulation of some kind. Blowing in something loose like cellulose is cheaper and would be easier to do yourself, but an expanding foam will fill the gaps more thoroughly, although both options have the potential of gaps forming due to settling or shrinkage.
The best choice for your projects depends on the climate you live in, as some materials are better at keeping out moisture. Only by considering all these options can you make the right choice.
If you are doing it yourself (DIY) then we recommend staying away from spray foam. Its very dangerous and most contractors need a special license, hazard insurance and special equipment in order to install it. Furthermore you have to buy it in 2 cans consisting of 55 gallons each.