WASHINGTON, D.C. (November 6, 2012)Â TheÂ Foam Sheathing CommitteeÂ (FSC) of the American Chemistry Council (ACC), through an industry effort, achieved an important change in gaining broad acceptance of a performance-based standard for the use of foam insulation products in all code complying commercial applications during the recent International Building Code (IBC) Final Action Hearings in Portland, Oregon. The International Code Council (ICC) approved for inclusion in the 2015 International Building Codes the Structural Building Components Association’s (SBCA)Â FS 100-2012: Standard Requirements for Wind Pressure Resistance and Foam Plastic Insulating Sheathing Used in Exterior Wall Covering Assemblies.
Why is Foam Sheathing Insulation being used more than ever before?
Residential housing design continues to move towards the development of high performance sustainable building systems. To be sustainable, a building must not only be efficient and durable but also economically viable. From this, new methods of enclosure design have been examined that provide high thermal performance and long-term durability but also take opportunities to reduce material use (including waste), simplify or integrate systems and details, and potentially reduce overall initial costs of construction.
One concept relating to enclosure design is to incorporate the use exterior foam insulating sheathing into the construction of the wall assembly. As with any building enclosure system, appropriate detailing for the management of water, vapor, and energy transfer are necessary.
Foam Material Properties:
There are three main types of insulating sheathing currently being used in the industry: Expanded
Each of these products all has a different set of physical properties that will affect the dynamic of the wall assemblies in regards to the transmission and management of heat and moisture.
Types of Foam
Insulating foam sheathings are split into two basic categories: 1) thermoplastics, 2) thermosets. Both EPS and XPS foams are thermoplastic foams, while Polyisocyanurate is a thermoset foam.
Thermoplastics are based on linear or slightly branched (non-cross linked) polymers. These foams have a definite melting range and will soften and melt at elevated temperatures. They are also more prone to react and degrade when in contact with some organic solvents as found in some paints, adhesives, and fuels.
Therefore it is important to only use manufacturer approved compatible materials when using thermoplastic foams.
Of the thermoplastic foams, EPS and XPS are the most common used in the industry. Both products are based on polystyrene resin and are considered to be closed cell.
The manufacturing of EPS involves the expanding of polystyrene beads to fill a mold. The densities of EPS foam can be varied if desired. Increased density results in increased thermal resistance and compressive strength. The density of the product also affects the vapor transmission. While EPS is a closed cell foam (slow water vapor and air transmission through the cell walls), the gaps between the cells will still allow for moisture to pass through the matrix. With increased density, these spaces are reduced and the ability of the foam to allow water transmission is reduced.
XPS foams are formed by mixing molten polystyrene with a blowing agent at the correct time, at an elevated temperature, and at an elevated pressure and then extruding the foam through a die to the atmosphere. This creates a more regular cell structure providing for better strength properties and higher water resistance that EPS foams. The density of XPS foams can also be varied, allowing for increased compressive strength, however due to the more regular cell structure, this has little to no effect on the vapor transmission properties.
Thermoset plastics are based on cross linked polymers. This will allow thermoset plastics to be used for higher temperature applications as they do not usually exhibit a melting range and will instead char and burn. Thermoset foams are also generally more resistant to solvents and chemicals.
The most common thermoset foam on the market is polyisocyanurate. While traditional polyurethane foams were created by reacting isocyanate with polyol (and other blowing agents, catalysts, and surfactants) polyisocyanurate foams can theoretically be created with no polyol, using only isocyanate reacting with itself (and other blowing agents, catalysts, and surfactants). In general though, commercial polyisocyanurate foam used in the market is really polyurethane foam modified with polyisocyanurate or a “blend” of the two foams. The use of the blend increases the fire resistance while maintaining the thermal resistance and strength of the material.
Polyisocyanurate Burn Video:
Many spectacular fires have occurred in foam systems applied to buildings, including the 2009
Monte Carlo fire in Las Vegas, the Borgata Water Club fire in Atlantic City in 2007, and the
Mandarin Oriental Hotel fire in Beijing in 2009.
With this recent code change with can only expect more fires invovling foam insulation. Please pass this information on and Stay Safe!
Lt. John Shafer