Most homes use external wall insulation in the form of batting and foam cladding.
However, if you have a solid exterior wall, you can’t use that insulation. Instead, you’ll have to add insulation to the wall cavity or to the interior of the home.
In addition, you might choose to individually insulate the interior walls of your home, even where they don’t connect to the outside.
Doing so can be expensive. However, it can also reduce your energy bills, reduce noise, and even improve the safety of your home.
This article will cover the pros and cons of insulating interior walls in both scenarios.
| Pros | Cons |
|---|---|
| Improved energy efficiency | High upfront costs |
| Increased resistance to mold over exterior insulation | Reduces interior space |
| Improves noise dampening | Increased dampness inside |
| Improved fire resistance | Disruptive |
4 Pros of Insulating Interior Walls
There are plenty of pros to installing insulation on interior walls. That’s true whether you’re installing insulation on the interior part of a solid wall or on stud and drywall interior walls.
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These primarily include improvements to energy efficiency, mold and mildew resistance, noise reduction, and fire resistance.
1. Improved Energy Efficiency
Any increase in insulation will improve how your home retains heating or cooling.
Here, you’ll see benefits whether the walls are against exterior walls or not. For example, the most value-added place to install insulation is on any surface that connects to the outside.
If you have, for instance, a solid exterior wall with a cavity and then an interior wall, installing insulation in your interior wall can greatly improve energy efficiency for your home.
That’s true whether or not you install cavity insulation at the same time. In most cases, you should.
Insulating walls in between unheated or low-heated rooms is also a good idea.
For example, if you don’t want to keep basements, attics, or laundry rooms and garages heated – you should insulate the walls between them. Doing so will provide you with an extra buffer to keep the cold out – reducing the amount of heat and cooling you lose.
In addition, if you have solid outer walls, internal insulation is cheaper to install than external insulation. That’s even true if you have to build a new stud frame to hold batting.
Of course, if you don’t have an existing stud frame, most contractors will install rigid insulation boards instead. However, both are cheaper than removing the external cladding and installing rigid insulation boards and weather boards under that.
In addition, you may want to insulate the dividing walls inside your home. These do not normally connect to the outside. Therefore, they’ll have a much lower impact on your heating and cooling bills.
However, they will allow you to maintain temperature differences between rooms. It will also reduce drafts by filling wall cavities that could result in hot and cold pressure areas.
2. Mold Resistance
If you choose between cavity insulation or interior insulation, the interior insulation is almost always more mold- and mildew-resistant. That’s because it has less exposure to the elements.
Installing insulation on the inside of your wall protects the insulation, so you’ll have to replace it less often.
That’s because cavity insulation directly touches an outside wall. When the temperature fluctuates, it will condensate and likely somewhere in the middle of the insulation. That can result in mold and mildew.
In addition, if the exterior or shell of your home is cracked or damaged, you won’t have to replace interior insulation. If your vinyl shell is cracked, it normally means the insulation will get wet and will become damaged.
Still, depending on the age of your home, the best answer may be to opt for both cavity insulation and interior insulation.
3. Noise Dampening
Insulation can improve the noise isolation of one or more rooms in your home. For example, if you share an interior wall with a neighbor, insulating that wall from your side can reduce the sound coming from your neighbors.
Similarly, you might want to insulate bedrooms, nurseries, and even laundry rooms to prevent hearing noise inside and outside those rooms.
Noise reduction isn’t the best reason to insulate. However, it can stack very well with improved heat retention in those rooms to be very worthwhile.
4. Fire Resistance
Good rock wool, fiberglass, or insulating boards will significantly increase the fire resistance of your drywall.
Here, you might also want fire-resistant insulation or a flame-resistant coating on your batting to ensure that your home is more fire-resistant.
In some cases, insulation can make your home more flammable. However, most insulation is designed to be as flame-resistant as possible.
4 Insulating Interior Walls Cons
While there are plenty of great reasons to install interior wall insulation, there are also plenty of reasons why you might not want to.
1. High Upfront Costs
Installing insulation will always cost a significant amount per square foot. For example, rock wool, one of the most common options for DIY jobs, will cost you an average of $1.40 to $4 per square foot.
Fiberglass batting is cheaper at an average of $0.65 to $1.50 per square foot. And, at 2 inches thick, spray foam insulation costs $3-$4 per square foot.
Of course, the good news is that you can often go room by room. This means you can spread costs out over time. Here, you can prioritize doing walls that touch the outside first. Or, walls that connect to low-heated rooms.
However, if you’re paying a professional to do the work for you, you’ll likely want to have everything done at once.
That’s because you’ll pay a large amount of service and location fees, which will add to the cost of insulating your full home if you have to pay them to come out multiple times.
2. Interior Space Concerns
If you’re installing interior insulation against a solid exterior wall, you will lose interior space. That’s true whether you go for an insulating board approach or a new stud and batting approach.
Here, the insulating board approach will normally require the least space. But, you’ll likely still lose about 2 inches of the wall.
If you opt to install new wall studs, insert batting, and then put drywall over that, you’re more likely to lose about 4” off the inside of every wall. That can be significant.
For this reason, if your home already has space issues, you might want to look into cavity insulation or external insulation.
However, chances are high that you already have an interior wall with wall studs. You can always install batting directly into that if it’s the case. In this case, you won’t actually lose very much internal space if at all.
3. Wicking Dampness Inside
If your insulation touches an exterior wall, it can wick dampness inside. That can be problematic if you have drywall.
Here, issues normally only happen with thin walls. Internal insulation keeps the wall at a steady temperature. So, when the temperature changes outside, the outside of the wall will condensate.
If the point is too close to the internal surface of the wall, the insulation will wick moisture inwards.
That can result in damp and damaged insulation. And, if the wall is particularly thin, it might also result in moisture bleeding through to the drywall. In this case, you’ll get damp patches on your interior wall.
The only way to avoid this is to ensure that you either have an air gap or a sufficiently thick outer wall. For this reason, cavity insulation isn’t always the best option. If you’re unsure, it’s a good idea to consult with an insulation specialist.
4. Disruptive
Installing insulation on interior walls means installing it under the existing drywall. That can be simple if you’re building the house or redoing the walls. In this case, you can simply install insulation as you finish the walls, before you put the drywall on.
However, most people who look into insulating interior walls aren’t remodeling or building. Instead, you’re probably looking for ways to reduce your energy bill and improve how your home stays warm. Doing so might mean stripping the existing drywall off.
In other cases, you can avoid this by using injection insulation. This expanding foam or cellulose fiber is installed through holes cut into the drywall or the exterior. It’s then injected into the wall at pressure and the hole is sealed up.
However, it also costs between $4 and $10 per square foot.
If you’re removing the drywall, you can minimize disruption by taking a room-by-room approach. However, this will also increase the total time of your renovation.
Best Insulation Materials For Interior Walls
There are dozens of different types of insulation and most of them are fairly multi-purpose. Here, your choice might depend on fireproofing needs, moisture resistance needs, and what’s available in your area.
In most cases, you’ll also want to check which R values are required for your area under here. However, providing you don’t buy insulation intended for garages or for outbuildings, chances are high that anything you buy will qualify.
Batting and Blankets
Mineral batting, most commonly rock wool or slag wool is one of the most common insulation options. At $1.50-$4 per square foot, it’s also expensive.
Here, you have to remove the drywall to install the insulation between the wall studs and joists. However, all batting is made to size to ideally fit those spaces.
Blanket insulation comes in a role, which is ideal for taking the same approach with a ceiling or a floor, between the joists and the flooring material.
Batting and insulating blankets also come in plastic fiber, fiberglass, and natural fibers. These range in cost from about $0.65-$10+ depending on the fibers.
Here, fiberglass and plastic are the cheapest you can get. That makes them the most popular option for DIY jobs. However, they may not offer the same insulating values as mineral insulation.
Insulating Board
Foam board, rigid foam, and rigid fiber insulation boards are good choices for putting on the inside of solid walls.
In addition, you can choose to put them on the inside of wall studs, between the cladding and the wall and on the inside of walls, between the drywall and the studs.
These boards are also used when you have to put insulation against solid walls. For example, if you’re insulating a concrete or brick wall, an insulating board is a good choice. These types of insulation normally start at around $2.75 per square foot.
This insulation is also a great choice for insulating poured concrete basements, because you can insulate them while losing a minimal amount of basement space.
Spray Foam Insulation
Spray foam insulation is ideal for homes that have already been finished. Here, spray foam is normally inserted using injection. It can be expanding or can simply fill the cavity. However, it normally costs between $3.15 and $7.50 per square foot.
However, it has many advantages. The biggest of these is that you’ll be able to install it with minimal disruption to your home. Instead, a professional installer will come out, make incisions in necessary walls, inject the insulation, and finish up.
In fact, spray foam is so fast that most jobs are completed on the same day. If you have a small home, it could even be finished in a few hours.
That’s a massive difference from a job that requires removing your drywall, installing batting, and putting the drywall back on.
Cellulose Loose Fill/Blow-In
Cellulose loose fiber and blow-in insulations are similar to spray foam in concept. In most cases, you need a professional installer who will make a cut in the walls and will inject the insulation that way. In most cases, the project will also finish in a day.
In addition, because cellulose is very often made up of recycled newspapers or similar materials, costs can be lower.
Blow-in insulation normally costs between $1.65 and $3.80 per square foot. However, this insulation is less-efficient than spray foam or similar high-density foam insulation. You’ll save money, but it won’t save as much on heating as a more efficient option.
For that reason, blow-in insulations are normally used in situations where the home is already built, costs are a concern, and the space isn’t high use. For example, in attics, garages, and basements.
If you’re using it for your whole house, you’ll want to use it in addition to another type of insulation, such as fiberglass batting or rigid foam boards.
Other Areas To Consider Insulation
It’s important to insulate any part of your home where it connects with the outside or with a low or unheated room. For example:
- Attic roof
- Attic between and over the floor joists
- Attic access door
- All exterior walls
- Foundation walls above ground level
- Between the exterior walls and the roof
- Flooring in crawl spaces and garages
- On concrete slab floors
- Joist spaces
- Basement
- Sheds or additions
If you haven’t insulated and sealed around doors and windows, you’ll also want to ensure you have that done.
Do All Interior Walls Need Insulating?
No. It’s not necessary to insulate all interior walls. For example, simple dividing walls, such as those delineating a hallway, may not be necessary to insulate. However, if you have separate heating in each room, it may be beneficial to insulate those spaces. In addition, filling the space between joists and studs can reduce airflow, which will improve energy efficiency.
Eventually, you want to ensure that you insulate any exterior wall and any wall in a non-heated space. You’ll also benefit from insulating walls that touch other homes, those that are near cooler spaces, or rooms that you’d like to keep warmer or cooler than the rest of the house.