There are many ways to reduce energy loss through house walls. In the 1970’s, standard wall thickness went from 2×4 to 2×6 for added strength, but also for added insulation. Modern construction now requires that all homes be built with the ability to insulate the sidewalls to R-19, typically requiring 5 1/2 inches of standard fiberglass insulation. One way to add more efficiency without adding a significantly larger amount of insulation is to create a thermal break in the walls. This method is not used often, but is very effective as an efficient building practice.
The Science Behind Thermal Breaks
A thermal break is simply a separation of materials. This concept is often used on steel windows and doors where the steel panels on the interior and exterior are connected by plastic or wood, creating a space or a break to prevent conduction of energy through the steel. Even though wood is not nearly as conductive, it still contributes to a large amount of energy loss. If you think about it from the point of view of total wall area that the framing makes up, it is fairly significant. For example, a 30 foot wall that is framed 16 inches o.c. (on center) has 24 wall studs that make up it’s framing plus a single bottom plate and two top plates. Each stud is 1 1/2 inch thick so you have a total wall area of 3 feet of wall that is nothing but wood. If the wall is 8 feet tall , that is 24 square feet! Creating a break from this allows the energy to be dissipated along another surface and allows the air in the cavity to act as an insulator, to some degree.
Thermal Break Wall Construction
Even though the exterior walls and interior walls are two separate walls, they still are required to be somewhat connected for structural purposes. Typically the exterior wall is a 2×6 wall insulated with R-19 fiberglass insulation with a 4 mil plastic vapor barrier attached to the interior of the wall. The secondary wall is typically a 2×4 wall that is completely uninsulated, but ties back to the main exterior wall with a 2×10, creating a 1/2 inch gap between the framing. Because of the significantly larger plate size, there is minimal energy loss at the plates.
Insulated Thermal Break Walls
Insulating the thermal break walls is the most energy efficient way of using thermal break construction. The exterior wall is typically insulated with R-19 fiberglass, and the interior wall is insulated with R-11 to R-13 fiberglass insulation. The thermal break still exists, but there is a significant value to having the insulation on the interior wall as well as it helps create and insulated air space between the framed walls.
Super insulated thermal break walls have 3-4 inches of closed cell spray foam insulation on them and require no vapor barrier because of the air sealing qualities and water repelling nature of the product. In this case, the entire exterior wall, including the framing is encapsulated in closed cell spray foam taking away a significant amount of energy lost through the framing and creating a monolithic surface. Fiberglass insulation further extends the thermal properties of this wall system, creating a 100% sealed cavity. Fiberglass insulation is designed to by concealed in an air tight cavity, so the thermal resistance is at an optimal level.
This type of construction is fairly expensive compared to regular construction as you are using twice the amount of lumber for the walls. If you are looking for extremely efficient wall insulation systems, however, this is one of the most efficient ways to insulate a home.