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How to Insulate Existing Walls

injection foam insulation | Existing walls insulation

How to Insulate Existing Walls Blog Feature
Amanda Ringler

By: Amanda Ringler on June 15th, 2022

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Cold spots and drafty rooms are tell-tale signs you need insulation in your existing walls, but you also need to know how to get the job done.

If you’re also experiencing high monthly energy bills, drafts coming through outlets, cold walls, and the dishes in the exterior wall cabinets are cold, then you need new or updated insulation in your walls.

Unless you are doing a remodel and gutting to the studs, there aren’t too many options for re-insulating existing walls. The two most common ways to insulate existing walls without tearing down drywall are injection foam and blown-in cellulose.

RetroFoam of Michigan has more than 20 years of experience insulating thousands of existing external walls across Michigan’s lower peninsula, so we have seen it all and know how to fix it all.

Insulating Existing Walls

In our ongoing efforts to educate homeowners, we have broken down the advantages and disadvantages of each insulation material, the installation process, and how much each one costs for insulating existing walls.

Here's everything you need to know about injecting or blowing insulation into existing walls.

Blown-In Cellulose Existing Wall Insulation


When it comes to adding insulation to existing walls, blown-in cellulose wall insulation is one of the two main options.

It is primarily made from recycled newsprint that conforms to most spaces without disturbing the structure or finish.

Pros and Cons of Blown-In Cellulose Existing Wall Insulation

While blown-in cellulose insulation can be a cheaper option for existing walls, it also has its drawbacks.

Blown-in cellulose in existing walls can add thermal insulation while providing some level of sound deadening, according to the Cellulose Insulation Manufacturers Association.

On the downside, the cellulose insulation can spill into the home through any openings in the wall cavities, like electrical sockets and furnace duct systems. Blown-in cellulose also allows for air leakage that contributes to a critical source of a home’s energy loss, as well as drafts, cold floors, and cold walls.

Blown-In Cellulose Insulation Cost

There are several factors that determine the cost of blown-in cellulose insulation.

The main factor in this instance would be the cost of hiring a licensed contractor.

The size of the area to be insulated is also another major factor when determining cost.

Injection Foam Existing Wall Insulation

injection foam insulation

Injection foam is an insulation and air barrier that will seal the existing external wall cavities against air movement. 

Injection foam wall insulation, like RetroFoam, is made up of a three-part resin designed to insulate enclosed cavities and has the consistency of shaving cream.

Pros and Cons of Injection Foam Existing Wall Insulation

Injection foam insulation tends to be a more expensive option compared to traditional insulation materials, but it does a better job of making a home feel more comfortable and lowers monthly energy bills.

It also is a cleaner material that doesn’t produce more dust around the home and will improve indoor air quality as it keeps allergens and pollutants from entering the home.

There can be issues with injection foam if the homeowner hires a contractor who doesn’t specialize in the material.

If the installers aren’t trained in injecting foam insulation into existing walls, areas can be missed and there could even be damage. If the injection foam isn't mixed properly, then it could lead to moisture issues in the wall cavity.

Injection Foam Insulation Cost

Much like blown-in cellulose, the size of the area to be insulated is the main factor when determining the cost to insulate existing walls with injection foam insulation.

The number of stories in a home, the type of siding, and the difficulty of the installation are also cost factors.

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Injection Foam and Blown-In Cellulose Insulation Installation Process

Reduce energy costs by insulating your whole house

Both injection foam and blown-in cellulose can be installed in existing walls through similar methods.

First a row of siding is removed and then a hole is drilled into each stud cavity. The insulation material is then injected or blown-in until crews know the cavity is full.

The hole is then plugged and the siding is replaced.

For homes with brick exterior, a hole is drilled into the mortar at the top, middle, and bottom of each cavity. The insulation is installed and the holes are filled.

Making the Best Insulation Choice for Your Existing Walls

The choice is yours now to decide if dense-pack cellulose or injection foam is the better fit for your existing wall insulation needs.

If you want to learn even more about the benefits of foam insulation, check out our Learning Center. If you have decided injection foam is the best fit and live in Michigan’s Lower Peninsula, give us a call at 866-900-3626 for a free estimate, or fill out the form on our website.

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About Amanda Ringler

Amanda previously has worked as a breaking news and crime reporter, TV news producer, and editor in Flint and Detroit. Throughout her career as a journalist, she has won several awards from The Society of Professional Journalists - Detroit Chapter and the Michigan Press Association. As part of the RetroFoam of Michigan family, Amanda uses her experience as a journalist to write content that will help educate homeowners on the benefits of foam insulation. When Amanda isn’t writing, she’s spending time with her husband and rescued huskies. She also loves knitting, making art, cooking, and hosting dinner and a movie night for friends and family.