Building Science

How to Reduce Thermal Bridging

The exterior wall of a building is the barrier that keeps temperature, moisture, wind, and pollution outside and creates a comfortable and healthy indoor environment. A primary goal of contractors and architects is to design a wall assembly with a thermal barrier that resists heat transfer between the inside and outside. Thereby the interior of a building stays warm in cold winter months and cool in the summer. A building's wall assembly resistance to this flow is measured by its effective R-value. The effective R-value includes all the materials used in its construction: the drywall, studs, fiberglass batts, plywood or OSB sheathing, water control plane, and siding. The larger the R-value, the lower the conductivities of the wall assembly. Problems in a wall’s assembly, such as thermal bridging, increase the wall’s conductivity, which leads to increased air flow through between the interior and exterior of the building. Building exterior walls with low conductivity and high effective R-values will keep unwanted outdoor elements outside and ensure a comfortable indoor environment.

Thermal Bridging Reduces the R-Value of a Building's Exterior Walls

A thermal bridge is a more conductive area of a wall assembly, compared to the surrounding space, like the stud space and the exterior insulation. Heat and energy flow through the thermal bridge at a higher rate than the surrounding areas; which reduces the effective R-value of the wall assembly. Thermal bridging typically occurs near highly conductive materials like wood studs, metal studs, steel, and concrete. For example, wood studs allow heat to flow through the wall at a rate that is three times faster than the heat flow through the insulation. So, even though the insulation has a nominal R-value of 19, the building’s effective R-value is lower. Steel framing is even more conductive than wood. In fact, steel framing typically reduces the surrounding insulation's R-value by as much as 50%, while wood framing reduces the surrounding insulation's R-value by less than 10%. Determining and preventing potential thermal bridges within a wall assembly is essential for constructing a comfortable and energy efficiency building.

Continuous Insulation Layer Stops Thermal Bridging

Wrapping a building’s envelope with a layer of continuous insulation cuts off thermal bridging. Stopping thermal bridging saves energy and lowers the risk of mold and rot by eliminating or reducing condensation. Continuous insulation is installed on the exterior of all areas of the building envelope except openings for windows, skylights, doors, and building service systems. Continuous insulation is required by ASHRAE 90.1 and 2015 IECC. ASHRAE 90.1 is the U.S. energy standard for all commercial and residential single or multi‐family structures greater than three stories in height above grade.The standard defines continuous insulation as insulation that is continuous across all structural members without thermal bridges other than fasteners and service openings.The amount of insulation required (as indicated by the R-value) by the standard depends upon its climate zone. Continuous insulation complies with building codes, eliminates thermal bridging and increases the effective R-value in a wall assembly.

Bautex Block Continuous Insulated Wall System

The Bautex Wall System continuous insulation stops thermal bridging and exceeds the energy efficiency requirements of the most strict building codes. The R-value for Bautex Blocks is R-14, without exterior or interior finishes. A building with Bautex Block continuous insulation with brick veneer is an R-18 system; far exceeding ASHRAE 90.1 recommendations. In warmer, southern climate zones, ASHRAE 90.1 minimum R-value requirements for continuous insulation (above grade, mass walls), are less than R-8. The Bautex Block is also fire-rated, noise-reducing, storm-resistant and easy to install. Interior and exterior walls of residential and commercial buildings can utilize Bautex Walls. The use of Bautex Wall System continuous insulation, stops thermal bridging, improves energy efficiency and saves building owners money for years to come.

Other Sources of Thermal Bridging - the Window and Doors

Thermal bridging also occurs through windows and doors. The addition of insulated shades and storm doors can reduce the thermal bridging through these openings.

Thermal bridging occurs in buildings near highly conductive, low R-value materials like wood studs, steel, and concrete. These highly conductive materials allow heat to transfer through the thermal barrier, usually the exterior wall. A proven method for eliminating thermal bridging is continuous insulation. Continuous insulation covers all parts of a building, eliminating thermal bridges other than those caused by fasteners, windows, doors, and skylights. Bautex Block is an excellent choice for continuous insulation. Bautex System’s lightweight stay-in-place insulated concrete block is a highly performing, strong, and simple-to-install wall system, with an R-value far exceeding industry recommendations. The Bautex Block gives contractors and architects an efficient method to eliminate thermal bridging; reducing energy loss and ensuring savings for owners of both residential and commercial buildings.