Expanding spray foam is a two-part chemical process involving isocyanate and poly resin, which when combined in the right mixture will expand 30 to 60 times it’s liquid volume. The material when fully cured becomes rigid and has a good resistance to heat flow. A product that has been growing in popularity and use over the past couple decades, spray foam has both advantages and limitations when used in home construction. This blog posting will be discussing two different types of foam, open and closed cell.
Polyurethane was invented in the late 1930’s by a German industrial chemist Otto Bayer. Different applications for the product were developed over the years, and in 1979 the process was first used in the construction industry. The process continues to evolve in both technology and application processes.
Open cell spray foam, sometimes referred to as ½ pound foam, is a soft insulating material with open cells. Because of its ability to absorb water and limited vapor retarding abilities, it is not a good choice of insulation for a northern climate. The perm rating for open cell spray foam is 30-35 per inch and has an R-3.5 per inch insulating value (about the same as fiberglass). One advantage is the cost, much cheaper to install than closed cell spray foam, but the needed addition of a vapor retarder, a class I or II may be required depending on the AHJ, will add to the installation cost.
Closed cell spray foam is more commonly used in cold climate construction. 2-pound foam, closed cell is much more dense than open cell, has a higher R-value at around R-7, and attains a perm rating of less than 1 (making it a class II vapor retarder)with the application of 2.5 inches (at least 3 inches is needed to achieve the required R-21 wall insulation level in climate zone 7). Other advantages of closed cell spray foam, it produces a very good air barrier and typically adds to the strength of the structure. Closed cell spray foam is one of the most expensive insulation choices currently available.
Spray foam can be applied at both high and low pressure. High pressure systems are typically only used by professional insulators and are applied at pressures of more than 1000 lbs. The equipment is expensive and requires extensive training to operate correctly. The 2 parts of the foam usually come in 55-gallon drums, making handling the material difficult. High pressure spray foam applications also tend to suspend foam particulates in the air. For this reason, the structure is recommended to remain vacant for 24 hours after insulating is complete.
Low pressure spray foam applications are often installed using lighter, more manageable product packaging. Referred to as a “box kit”, pressures in these systems are usually under 100 lbs. Box kits can be purchased at the big box stores, some lumber yards and on-line. Professional insulators often use these systems for small jobs or touching up existing foam applications. They are also used by non-insulation contractors and DIY’ers. Spray foam applications using low pressure systems have traditionally been much slower. I did recently see a demonstration of a low-pressure spray foam delivery system where the application speed was close to the high-pressure system. The advantage to this system is the building can be reoccupied after 1 hour.
The code requirements for all foam insulations, including spray foam is found in the 2012 IRC (the current code in force for the state of Minnesota) in section R316.
Section R316.4 Thermal barrier. Unless otherwise allowed in Section R316.5 or Section R316.6, foam plastic shall be separated from the interior of a building by an approved thermal barrier of minimum ½ inch gypsum wallboard or a material that is tested in accordance with and meets the acceptance criteria of both the Temperature Transmission Fire Test and the Integrity Fire Test of NFPA 275.
Basically, all installed spray foam must be covered by ½ drywall or equivalent in dwellings. Many insurance companies also require accessory and out building also have spray foam covered. When plastic foams burn, the gases produced by the burning foam is itself combustible. When enough quantity of the gas is present, a flash fire is produced. This type of fire is short but can be very powerful and destructive.
A downside to spray foam is its effect on the environment. Hydrofluorocarbon is the blowing agent used to apply the foam, which has a high global warming potential. Not good for the environment. Hydrofluorocarbon is scheduled to be replaced by hydroflourolefin, a blowing agent better for the environment, by 2021.
The application of any spray foam requires the use of personal protective equipment (PPE). Professional installers have very good, and very expensive fresh air delivery equipment and also wear protective suites, gloves and eye protection. The chemicals used in spray foam applications are bad for you. Breathing the chemicals used in the application can cause a reaction requiring medical attention. Prolonged exposure can create lifelong breathing issues. Proper protection is critical.
Another concern is its application during cold weather. Air and surface temperatures must be above 40 degrees. If applied to surfaces below 40 degrees, shrinkage of the product and proper adhesion to the surface becomes an issue. Air leaks in building envelopes that have been insulated with spray foam can be very difficult to find.
My last major concern is with the crew applying the product. Have they been properly trained? Most problems arising from spray foam is improper installation. Not only does the insulating contractor need be educated, but the employees who are often the people installing the product, need education. I’ve heard of buildings burning down because of improper installations. (The chemical process of combining isocyanate and poly resin creates heat, if too much of the foam is dispersed in a single lift, the temperatures in the foam can become high enough to burn materials.) Be sure you know who you are hiring.
I have used closed cell spray foam as an entire home insulation strategy in several projects with good results. Recently, my use of the product has become more of a spot insulation, mostly to reduce project costs. I use closed cell for hard to insulate areas such as rim joists, around penetrations, and fireplace chimney chases. Another situation I would use it is in remodeling of older homes. It’s air sealing properties make it a good choice for homes with comfort issues.
Spray foam is a good product with many applications if used properly. There have been issues with the product but if you find a good, knowledgeable installer, it can simplify some building systems.