an unfinished attic with knee wall insulation that says "worth it?" in green and orange text

Knee walls are incredibly supportive and often overlooked when it comes to insulation. If your home has knee walls (and there’s a high chance it does), it’s essential to consider the pros and cons of insulating them. What are the benefits of knee wall insulation?

Knee wall insulation prolongs your home’s structural integrity, helps you stay much warmer, reduces energy losses, and saves more money on your monthly energy bills by managing temperature fluctuations.

Throughout this post, I’ll explain everything you need to know about knee wall insulation and whether it’s right for your home. I’ll go over the common materials used for knee wall insulation and whether it’s energy-efficient and eco-friendly. I’ll also share some tips and tricks for performing DIY knee wall insulation, so check it out!

Do Knee Walls Need Insulation?

Getting high-quality knee wall insulation can make a world of difference.

The knee wall supports angled timber typically found in the attic. Unfortunately, this wall doesn’t have any insulation, meaning there’s a lot of space for thermal bridges to push and pull the temperature through the roof.

Installing knee wall insulation works the same way as all other wall insulation. You’ll have to choose the material, cover the spaces between the studs, and decide how to adhere it to the surface.

Most people use insulation staples for fiberglass insulation batts and insulation glue for foam boards. Cellulose insulation typically fills massive spaces without adhesives.

The Types of Knee Wall Insulation

Retro Foam of Michigan lists these as the best knee wall insulation materials:

  • Cellulose
  • Spray foam
  • Fiberglass

You can choose from many types of green insulation if you want to reduce your carbon footprint. Eco-friendly insulation has come a long way, with most kinds offering as much (if not more) R-value as traditional home insulation materials.

Let’s delve into each of the primary types of knee wall insulation without further ado.


Cellulose is one of the most eco-friendly insulation materials available for knee walls.

A pair of cupped hands holding cellulose of the type that is often used to insulate interior walls.
Cellulose is an eco-friendly material that can be used to insulate interior walls.

Cellulose is made of recycled newspaper and other paper supplies, then blown into the insulation supports such as studs, foam boards, etc. It has an R-value of 3.5.


  • It’s exceptionally eco-friendly, which reduces your carbon output.
  • Cellulose installs fast because it’s blown in.
  • It’s affordable compared to most high-end insulation materials.


  • Cellulose is flammable and should be protected by wood or foam insulation boards.
  • Excessive humidity can compress cellulose, so you must add more every decade.

Spray Foam

Spray foam is one of the most popular types of insulation for almost any in-house project.

It’s incredibly straightforward: Nail a flat wooden board behind the knee wall (if it only has supportive studs), then spray the wall with the foam between each stud.

Spray foam insulation expands a lot, so don’t add too much. It has a 3.8 R-value per inch.


  • It’s one of the easiest ways to insulate the knee walls in your home.
  • One can of spray foam insulation covers most of a knee wall.
  • Spray foam is quite affordable since it’s mass-produced and readily available.



Fiberglass is another common insulation material for knee walls because it’s affordable and eco-friendly.

Much like cellulose, fiberglass insulation is mainly made of recycled materials (glass, in this case). As a result, most fiberglass insulations have a 2.7 R-value per inch.

Fiberglass insulation being installed in the underside of a home attic ceiling, showing a beige fiberglass batt
Fiberglass insulation is a green solution for insulating your home’s knee walls, and it has an average R-value of just under 3 per inch.


  • Fiberglass offers a unique, long-lasting way to reduce your environmental impact.
  • It can last for up to two decades, making it incredibly reliable.
  • It comes in rolls that you can flatten and apply quickly.


  • You must wear protective gear because fiberglass is itchy and can cause respiratory issues.
  • It doesn’t offer as much insulation as the other materials above.

Is Knee Wall Insulation Energy-Efficient?

Knee wall insulation is very energy-efficient!

How so? This form of insulation prevents thermal bridges, energy losses, and excessive humidity in your home.

In addition, placing insulation in the knee walls makes your home much more comfortable and enjoyable while preventing roof insulation corrosion.

Dr. Energy Saver explains that insulating a knee wall reduces the energy your thermostat uses to heat or cool your home.

Thermal bridges are the main thing working against your attic’s insulation. So whether you have knee walls in your attic, home additions, or anywhere else in the house, you should be cautious of thermal bridges.

They let temperatures move through various surfaces, so you have to use your HVAC system to adjust the temperature more often.

Does Knee Wall Insulation Reduce Your Monthly Bills?

Knee wall insulation reduces your monthly bills by using less energy to heat and cool your house.

The insulation also prevents the existing warm or cold air from leaving through the roof.

Your home is heated by many other things aside from the HVAC system. For example, body heat, ovens, TVs, space heaters, and other factors will adjust your home’s temperature.

If you have high-quality knee wall insulation, it’ll retain as much of that heat as possible. You’ll save more money on your heating bills in the long run.

Another way that knee wall insulation reduces your bills is that it prevents moisture from rotting the wood around your home. Condensation develops when a wall isn’t insulated and there’s a cold or hot front.

Installing insulation on a knee wall prevents insulation, drastically reducing the risk of mold, mildew, wood rot, and more. You won’t have to worry about repairs as often.

Why Is Knee Wall Insulation Eco-Friendly?

Knee wall insulation is eco-friendly because it lowers energy consumption, prevents wood rot, and reduces your home’s carbon output.

Many knee wall insulation materials are made of recycled supplies, further reducing the home’s carbon footprint.

Being eco-conscious has more benefits than reducing your effect on the environment!

Many utility companies offer reduced energy compensation via tax credits. Check your local state laws to know whether you can save by switching to eco-friendly knee wall insulation.

So, why is knee wall insulation great for the environment?

  • You don’t need to use as much energy, which means you won’t produce as much carbon via burning fossil fuels.
  • Multiple eco-friendly insulation materials are available to protect your house’s knee walls.
  • Lowering the condensation will reduce your repair frequency, which means you won’t have to use as much wood and other materials as often.

Knee wall insulation is a no-brainer whether you’re after the financial advantages or the environmental benefits.

Knee Wall Insulation Installation Tips and Tricks

A homeowner wearing a dust mask removes old fiberglass insulation from a wall
Always wear protective equipment when working with fiberglass to protect yourself from injury.

When installing knee wall insulation, follow these tips and tricks:

  • Clean the surface before adding insulation. Never add insulation to a dirty knee wall. Not only will it prevent the insulation from achieving the closest contact possible, but it can also cause the insulation to slip. Whether using staples, adhesives, or spray foam, you should clean and dry the surface beforehand.
  • Consider the climate you live in before choosing the insulation material. For example, fiberglass insulation won’t be the best choice if you live in a humid and rainy area. This is because it compresses, as does cellulose. Instead, you could choose spray foam insulation. Cork insulation is also an eco-friendly option.
  • Fill the gaps between insulation sections with spray foam. Spray foam quickly expands to fill the cracks between any insulation. You can also use it between foam boards if you want to add an extra layer.
  • Put foam board insulation over the knee wall to reach a higher R-value. Home Trust Remodeling recommends keeping knee wall insulation around R-13 to prevent thermal bridges and energy losses. Adding foam insulation boards over each section of the knee wall insulation will bring you closer to this recommendation.
  • Inspect the knee wall insulation after each winter. Humidity and colder temperatures can wreak havoc on knee wall insulation because it always works against gravity. If the insulation material looks slumped or compact, add a new layer. If this keeps happening, switch to spray foam insulation or combine adhesives with staples.

Final Thoughts

Opt for insulation if you have knee walls in your house. Your home will feel warmer while lowering your energy bills and preventing drafts. Choose between cellulose, fiberglass, and spray foam insulation, then enjoy the long-lasting benefits.


Dr. Energy Saver: Insulation – Making Knee Wall Spaces Energy Efficient

Retro Foam of Michigan: What is the Best Way to Insulate a Knee Wall?

Home Trust Remodeling: Knee Wall Basics Including How to Insulate

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