A Pennsylvania company has developed an alternative to wood window bucks, claiming the coated polystyrene bucks offer better thermal insulation, a more effective water and air seal, and better long-term performance.
Window and door bucks are used when exterior insulation, such as rigid foam, or a rainscreen is installed over sheathing on exterior walls. A buck (more properly called a Rough Opening Extension Support Element, or ROESE) ensures the window or door will be aligned correctly with the insulation or rainscreen.
Carpenters typically make bucks out of wood. But wood bucks have some drawbacks, says John Brooks of BRINC Building Products, including a tendency to warp and shrink. In addition, wood has a relatively low R-value, so wood bucks represent a thermal bridge in the building envelope.
So Brooks invented the ThermalBuck, an L-shaped component made from high-density expanded polystyrene encased in a blend of polyurethane and polyurea. ThermalBuck has a compressive strength of 52 psi and, according to the company, can handle hurricane force winds with “minimal permanent compression.”
Mitered pieces of ThermalBuck are nailed into a rough opening for a window or door in a bed of adhesive. (Brooks specifically recommends Dow Corning 758 adhesive.) Then the window or door is installed with the flanges caulked and nailed to the outside face of the buck.
Four sizes are available
ThermalBucks come in 8-foot lengths and in four versions, corresponding to insulation or rainscreen thicknesses of 1 inch, 1 1/2 inch, 2 inches, and 2 1/2 inches.
The tongue (the part of the buck that wraps around the inside of the rough opening) is 1/2 inch thick and extends into the opening 2 1/2 inches, no matter which ThermalBuck you buy. The other part of the “L” differs depending on the thickness of the exterior insulation. The bucks are pitched slightly toward the outside of the wall, and they are treated with an insecticide to prevent termite infestation.
Brooks rolled out ThermalBuck at the GreenBuild conference in Washington, D.C. last fall, where it won a “Greenest of the Green” award. ThermalBucks cost between $2.50 and $3.20 per foot. For ordering information, contact the company through its website.