Thermal bridging in walls, and how to stop it
A thermal bridge is a conductive path that bypasses the insulation. In a framed wall the studs and plates are the bridge, and they can cost a wall a third of its rated R-value.
What a thermal bridge is
Heat takes the easiest path out of a building. Insulation is designed to be a hard path; anything conductive that crosses it is an easy one. In a stud wall the studs, the plates, the headers and the rim joist all run straight from the warm side to the cold side. That is a thermal bridge.
Wood conducts heat roughly four times better than the insulation between the studs. Steel conducts it hundreds of times better. So a steel-framed wall with insulation only between the studs performs far below the number on the insulation bag.
Why the R-value on the bag is not the R-value of the wall
An insulation product is rated in a laboratory as a uniform slab. A wall is not uniform: it is insulation interrupted every 16 or 24 inches by a stud, and interrupted again at every corner, opening and floor line.
The honest figure is the whole-wall R-value, which accounts for the framing. Framing factors of 20 to 25 percent are common in residential construction, and the effective R-value drops accordingly. This is why two walls with the same nominal insulation can perform very differently.
How the bridge is broken
There are three approaches. Add continuous insulation outside the framing so the studs no longer touch the exterior. Use a framing member that is itself less conductive. Or change the geometry so no single member spans the assembly.
A structural panel takes the third route: the insulating core is continuous through the panel, and the structural members are set into it rather than passing straight through.
What Guardian publishes
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In a Shield™ panel the cold-formed steel is integrated into the EPS opposed on the inside and outside specifically to eliminate thermal bridging and produce a structural composite super energy efficient panel.
Source · Shield™ Technical Product Description
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Published wall values: 9¼ in R-38 at 40 °F and R-35 at 75 °F; 7¼ in R-30 and R-28; 6 in R-25 and R-23.
Source · 3-Part Specification 1.5 E.5 b
Go deeper
Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus
ASTM C578Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation
Panel typeLoad-bearing exterior walls
FAQWhat is thermal bridging and how does the panel avoid it?
FAQWhat R-value do Shield™ panels achieve?
Written by Data Subsystems, for Guardian Structural Technologies. Last updated .
Drafted from Guardian Structural product literature and published building-science sources. Awaiting Guardian technical review. Confirm any figure against the current product documents or ask us before you rely on it in a design.