Why Spray Foam?

Many of us know that insulation is a major component for keeping your building cool during the summer and warm during the winter. There are many different types of insulation but why is spray foam the preferred?



Batt Insulation – is probably the most common and most familiar to most people. Batt insulation is best used in wall assemblies and can come with or without an attached vapor barrier (also known as faced and un-faced insulation). The vapor barrier not only allows for vapor control but allows for the placement of the product much easier. It is important to know whether the vapor barrier is not only needed but required by code, or in some cases required to not be installed. This will depend on your climate and the permeability rating of the other materials in the wall assembly.

Blown-in Insulation – This is typically used in vented attics placed on the top side of the ceiling finish. Blown-in insulation is easy to install but tends to settle over time allowing trapped air to escape and reducing its R-value (unit of thermal resistance).

Spray Foam Insulation – This is often considered far superior to the more traditional systems but can be more expensive. Using spray foam cuts down on your home’s air exchanges. No home is 100% sealed because of cracks and gaps between different building materials. Air is constantly passing inside and out of your building this is what is called an air exchange. Spray foam seals these gaps because of its fluid-applied and expanding nature. This air impermeability reduces the amount of air movement through your wall and ceiling assemblies by an extreme amount. Spray foam insulation, when applied directly to the underside of the roof sheathing allows for attic encapsulation. Attic encapsulation eliminates the need to vent your attic and allows it to be a part of the conditioned space making the home far more energy efficient.

Attic Encapsulation: Why it is Better – You hear most folks in the construction industry talking about how important it is for the “home to breathe.” Why this is true it can often be misunderstood when discussing attic encapsulation. Vented attics are more common in the States because they keep your roof cold enough in the winter to prevent ice damming during a snow thaw and cool in the summer to prevent your shingles from overheating and having a short life expectancy. Here’s where it becomes an issue. Insulation and more specifically its R-value is based upon a standard temperature differential of 50 deg Fahrenheit. As the temperature between two spaces increases the r-value or thermal resistance decreases. With a vented attic the temperature differential in the middle of winter and in the hottest part of the summer is at extreme levels. During the summer, attics can be as hot as 150 deg due to the greenhouse effect created by the shingles. If the home in the summer is being cooled to 75 deg that means that your attic insulation is separating two spaces that have a temperature difference of 75 deg. This drastically decreases the insulation’s effectiveness.  An encapsulated attic on the other hand places the insulation directly against the roof sheathing allowing the attic to be conditioned to match the home. This insulation is now separating two spaces with a temperature difference of closer to 25 or 30 deg on a hot summer day making it much more effective. Another important note I will make about encapsulation is that unvented attic encapsulation can only be done, at least that I know of, with spray foam insulation. Placing batts against the roof sheathing does not create enough of a seal and will still need venting. This type of venting is done through a baffle system. More on that in another post.

Differences in Spray Foam: Spray foam comes in two types, open cell and closed cell.

Closed Cell Foam is usually more expensive but offers a few benefits.

  1. It can be considered structural. When I say structural, I mean that it can provide lateral stability. Please do not try to make a beam out of the stuff. Closed Cell foam when dry, is rock solid and bonds to the materials it touches. According to some studies, the lateral strength of the sprayed assembly can be triple when using closed-cell foam versus open-cell.
  2. Higher R-value per inch. Closed cell foam has an r-value of up to R7 per inch. This is twice the amount of some open-cell spray foam.

Open Cell foam has a few upsides as well compared to closed.

  1. Open cell is considerably cheaper, or at least it used to be. I would price both if it were me building a home. I am not sure about the price difference now but if you have the room in your attic for an open cell foam it will probably save you some money in material cost.
  2. Open-cell foam is lighter and easier to remove. If there is ever a day when you need to make a change you will wish you went with open cell. Because the open cell is less dense it is also softer and will make your future demolition a little easier

Building codes and more specifically energy codes are always changing and in most cases are getting stricter. It won’t be long before products like spray foam are the most effective way to meet the new standards. These products may cost more but they offer more sustainable energy practices.

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