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Foam vs Fiberglass vs Cellulose: Which Insulation is Best for My Existing House?
Amanda Ringler

By: Amanda Ringler on March 29th, 2017

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Foam vs Fiberglass vs Cellulose: Which Insulation is Best for My Existing House?

Best existing house insulation  |  cellulose insulation  |  fiberglass insulation  |  Foam Insulation  |  insulation

You know your home is in need of insulation, but now comes the tough decision – do you use spray or injection foam, fiberglass, or cellulose?

Choosing the right home insulation can be a daunting task while you take into consideration the cost of the material, how effective an insulation material will it be, and will it end up saving you money in the long-run.

RetroFoam of Michigan has more than 15 years of experience insulating thousands of homes across the lower peninsula, so we know quite a bit about all insulation materials.

In an effort to provide our customers with all the information available so they can make an informed decision, we have information about each area of the home and which insulation materials work in those spaces.

Let’s take a look at the existing house starting at the top and going all the way to the bottom.

Best Attic Insulation: Cellulose vs Fiberglass vs Spray Foam

attic fiberglass insulation

If you’re looking to cut down on the amount of money pouring out through your roof, attic insulation is the way to go.

High energy bills and the inability to maintain a constant temperature are just some of the signs your attic needs new or updated insulation. The best insulation options for an attic are open cell spray foam, fiberglass, and cellulose.

Cellulose is the oldest insulation material used for not only the attic, but other areas of the home as well. Cellulose can be either a loose-fill or blown-in material and is primarily made of recycled newsprint or denim.

Cellulose can be a DIY project and is fairly inexpensive when it comes to insulating attics in comparison to other insulation materials. On the flip-side of that, cellulose can settle up to 20 percent, can shift to one side of the attic, and it doesn’t create an air seal. This means cold and hot air can move freely through the attic without any barriers, raising monthly energy bills.

Fiberglass is another traditional insulation material that consists of extremely fine glass fibers.

Fiberglass can be installed as a DIY project and is inexpensive. The downside of fiberglass is that the fibers it is made up of can be inhaled and even embed in the skin. It also still allows for airflow into the attic.

Open cell spray foam insulation is an air barrier material that creates a seal against air movement. It can expand up to 100 times its original size, filling every nook and cranny in the attic. It’s main ingredients are water-blown and organic chemical compounds derived from petroleum extracts making it environmentally safe.

Spray foam is Class One Fire Rated for the attic, which means it won’t serve as a catalyst if there were a fire. It also doesn’t retain water that will promote mold and mildew growth, it creates an air seal that helps lower monthly energy bills, and creates a semi-conditioned space by insulating the roof deck in an unvented attic.

The downside of spray foam is that it is more expensive than traditional forms of insulation and is too complex for a DIY project, so a contractor must install it.

Best Existing Walls Insulation: Blown-In Cellulose vs Injection Foam

injection foam insulation

When it comes to the existing walls of your home there is no easy way to tell you this, but the insulation must be installed by an experienced contractor. The good news is you can add insulation to the existing walls without removing your drywall and the extra expense of a full remodel.

Injection foam insulation and blown-in cellulose can be installed in the existing walls through similar methods. First a row of siding is removed, a hole is drilled into each stud cavity, the material is then injected or blown-in until the cavity is full, the hole is plugged, and the siding is replaced.

When insulation does its job, it impacts the conduction (heat transfer) and the convection (air flow), which can both impact the comfort and energy efficiency of your home.

More traditional forms of insulation, like cellulose, is resistant to heat that is transferred through conduction. During the winter months, that heat transfer is from the inside of your home to the outside and vice versa in the summer.

Air flow allows the movement of air in and out of your home through gaps in the walls and electrical outlets.

This air leakage contributes to a critical source of the home’s energy loss. It also contributes to discomforts such as drafts, cold floors, and cold walls.

To reduce this air leakage, foam insulation works best because it provides heat resistance and an air seal.

Best Crawl Space Insulation: Fiberglass vs Spray Foam

Crawl space spray foam insulation

The best materials to use in insulating the crawl space are fiberglass and spray foam.

The walls of the crawl space should be insulated with a non-water sensitive insulation that will prevent interior air from touching the cold surfaces. Allowing the interior air that is regularly full of moisture can cause condensation and promote mold and mildew growth, according to the Building Science Corporation. 

The crawl space can be an area that sees more moisture than other areas of the home.

This doesn’t make fiberglass a great fit for the area. When fiberglass gets wet, the water accumulates in the pockets of the material and drastically reduces its insulating properties. This means you will have to replace it if you want your insulation to work down there.

Spray foam is the better choice between the two because it doesn’t retain water and it creates an air seal. Fiberglass is the cheaper option and you can install it yourself, but spray foam creates the air seal you will want in the space.

The Building Science Corporation recommends a foam based insulation material for crawl spaces because of this.

Best Rim Joist Insulation: Fiberglass vs Spray Foam

Rim joist

The rim joist is one of the most overlooked areas of the home when you are looking for the culprit causing drafts around your floor boards.

The insulation options for the rim joist is spray foam or fiberglass.

Fiberglass is inexpensive and you can install it yourself, but it does not do as good of a job insulating the rim joist, according to Home Construction Improvement. The material when installed in the rim joist also is prone to mold issues as it holds condensation against the wood, which leads to mold and decay formation.

Spray foam doesn’t retain water, so it doesn’t have the same moisture issue as fiberglass. It will also create an air seal that keep the outside air from getting in, while reducing the drafts near the floor board.

Fine Home Building recommends only air impermeable insulation for the rim joist – either spray foam or rigid foam boards.

Making the Best Choice for Your Existing Home Insulation

At the end of the day, the choice is yours when it comes to selecting the best insulation for your existing home. To see what makes the most sense for your family you will need to take into consideration the pros and cons of each material, the goals you are looking to accomplish and your budget.

Overall, if you are looking for the best long-term solution, foam insulation products will create the air seal in your home that will make it more comfortable while saving you money on your monthly energy bills. Foam insulation doesn’t settle or sag and it fills all the nooks and crannies where it is installed.

If you agree with Fine Home Building and the Building Science Corporation that foam insulation is the best fit for your existing home 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 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.