Spray Foam vs. Fiberglass Insulation: Which is Right For Your Situation?

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At The HeatBusters, we get asked a lot about the differences between spray foam insulation and a fiberglass insulation + radiant barrier + solar attic fan combination. These two products often get lumped into the same category because they both carry the word ‘insulation’ in their descriptions. However, they each carry different properties and both have their own distinct and unique advantages.

What’s the Skinny on Spray Foam?

The concept behind spray foam is to completely envelope the building/home from the outside. This seals off and prevents any air exchange in the structure. In other words, no incoming or outgoing air exchange can occur. This is in opposition to the fiberglass insulation/radiant barrier combo, which is dependent upon a ventilated building. A properly breathing attic space is the key to this combination’s success, which requires fresh air in and moist, hot air out.

Spray foam is a great energy efficiency method to utilize when building a home from the ground up. Installing foam into the wall and attic space is the only way to create a true envelope. In a retrofit situation, adding spray foam into the attic space only creates an incomplete envelope and generally results in a partial improvement at a higher cost. Think of the structure in this example comparable to an igloo cooler which is insulated by a version of spray foam. Having insulated walls is as important as having an insulated lid. In a retrofit situation, only the ‘lid’ of the home is being insulated.

Although we do have experience with it, The HeatBusters is not a spray foam insulation company. One reason that we typically do not recommend spray foam in a retrofit is that homes are almost never built or designed with the intentions of cutting off all ventilation. There are steps that must be taken in order to properly make this conversion and those steps equate to additional money spent. If ventilation is not correctly sealed off, this will lead to mold issues down the road since moisture is now being trapped in the structure.

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Advantages of the Fiberglass Insulation/Radiant Barrier Combo

In most cases, homes or other buildings are designed to accommodate a fiberglass insulation + radiant barrier style of retrofit. They already have a ventilated attic space and no major overhauls are necessary to reap the benefits of these products. Unlike spray foam insulation, it is not necessary – or preferred – to seal off the outside from the inside.

Radiant barriers are dependent on a ventilated system. This product is 95% reflective and 5% emissive. This means that 5% of radiant heat is still making it through the foil. While most hot air is blocked from entering, it is essential that the hot air that does enter has somewhere to go. This is why proper ventilation is absolutely necessary. Solar attic fans are our preferred method of ventilation, as they produce the best results. Cost is also a part of the equation when determining what is best for you and your home. Fiberglass insulation tends to be roughly half the cost of spray foam insulation.

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Keeping the Heat Off

At the end of the day, these methods are all utilized to keep as much of the heat burden off the insulation as possible. If the insulation is asked to battle a 100° attic space versus a 150° attic, it will be able to perform much more efficiently. Insulation is like a sponge. If you pour water onto a sponge, it will hold water for as long as it can. Once maximum saturation is reached, the excess water will begin to leak. Insulation works the same way with heat. It will hold as much heat as it possibly can. Once the maximum potential of the insulation is reached, the excess heat will begin to leak and move towards the cooler air space it inhabits: the inside of your home.

There admittedly are particular situations when spray foam is a superior solution, usually new builds. There are also times when fiberglass insulation makes more sense, usually retrofits. While our intention is certainly not to disparage any product or provider, we feel it is important to define the differences between insulation types – and their preferred uses – for our customers. Contact us today to speak with our expert energy efficiency consultants!