On paper, wall insulation numbers can look straightforward. An R-19 or R-21 batt between steel studs may seem sufficient, but that number doesn’t reflect how the finished wall will perform once built.
Steel lets heat pass through about 400 times more easily than wood. With steel stud thermal bridging, cavity insulation can lose about 30% to 50% of its thermal resistance. In one ORNL test, the loss was about 48%. That drop can leave a wall performing below the level it was designed to meet.
Using a thicker batt doesn’t always solve the problem. Continuous insulation on steel framing covers the frame instead of stopping at each stud, reducing the thermal path through the steel. For steel-framed projects, continuous insulation is also increasingly part of meeting energy-code requirements.
For builders in New York, New Jersey, Pennsylvania, Connecticut, and Delaware, it’s worth working through the insulation assembly before the framing is closed in.
Why Steel Framing Behaves Differently
Than Wood
The Thermal Bridging Problem, Explained
A thermal bridge is a part of the wall where a conductive material gives heat an easier path around the insulation. Steel studs create that path.
Steel has an R-value of only about 0.04 per inch. Wood is roughly R-1 per inch, while rigid insulation ranges from about R-3.2 to R-6.5 per inch, depending on its density.
These numbers show cavity insulation ratings can be misleading when you consider the R-value of steel studs. The batt has its own R-value, but each steel stud interrupts the insulated space and creates another path for heat through the wall. That’s why metal stud wall insulation needs to be considered as part of the whole wall, not just what sits between the studs.
This matters more in steel-framed multifamily and commercial buildings than in wood-framed single-family construction. Wood framing also creates thermal bridging, but steel lets heat pass through much more easily.
When planning new home insulation, builders should consider the framing material to better understand how the finished wall will perform.
The Real Numbers — How Much R-Value You Actually Lose
From ORNL’s Own Test Data
Hot-box tests show that the number on the insulation label can differ significantly from how the finished wall performs.
Researchers estimated that metal framing can reduce “in-cavity” thermal resistance by 30% to 50%. In one test, a wall with 3½-inch, 18-gauge steel studs spaced 16 inches on center and R-12 mineral fiber batt insulation lost about 48% of its R-value.
This difference is called the framing effect, which is why the whole-wall R-value matters. A batt may be rated R-12, R-19, or R-21, but that number doesn’t account for everything in the finished wall.
Corners, headers, roof-to-wall joints, and other details can reduce performance even further. In modeled assemblies with one inch of exterior EPS sheathing, whole-wall R-values were about 19% to 27% lower than clear-wall values.
The R-value listed on insulation is not always the same as the R-value the finished wall delivers. That difference is what framing effect R-value calculations are meant to capture.
Cavity insulation plays a role, but it cannot solve the thermal bridge created by steel. Builders may use spray foam insulation in cavities or as part of continuous insulation coverage. But changing the cavity material alone doesn’t remove the heat path through the steel.
Continuous Insulation Is the Fix — And Increasingly the Code Requirement
Why CI, Not Just More Batt
The main difference between cavity insulation vs continuous insulation is where it’s installed.
Cavity insulation fills the space between framing members. Continuous insulation, or CI, covers the framing in an unbroken layer.
Continuous rigid insulation can be added over wood or metal framing to reduce thermal bridging. Because it covers the studs, it limits the heat path that cavity insulation misses. The effect is more severe with steel because steel conducts heat much more easily than wood.
With continuous insulation steel framing assemblies, the exterior layer helps cover the studs instead of stopping at each one. That’s why exterior insulation steel framing systems can improve whole-wall performance rather than simply increasing the cavity R-value.
Energy codes increasingly account for thermal bridging. The required R-value and CI combination, however, depends on the code and project location. Builders need to confirm what applies to each job.
Climate zones also need to be verified at the county level. For example, Union County, New Jersey is classified as Climate Zone 4A, Mixed-Humid. Knowing the county’s climate zone matters most for multifamily insulation jobs, where steel framing and code requirements often overlap.
Air sealing is another part of the wall assembly inspectors look at. Heat can escape through gaps and penetrations as well as through the steel framing.
FAQ
Does steel framing really cut insulation performance in half?
Yes, it can. Metal framing can reduce in-cavity thermal resistance by 30% to 50%. In one test, a steel-framed wall lost about 48%. The exact loss depends on stud gauge and spacing, and the type of insulation used.
What is the difference between cavity insulation and continuous insulation?
Cavity insulation goes between the studs. Continuous insulation covers the framing in an unbroken layer with no breaks at each stud. This helps reduce thermal bridging insulation losses through the framing.
Can spray foam alone solve thermal bridging in a steel-framed wall?
No. Closed-cell foam can insulate the space between the studs, but it does not stop heat from traveling through the steel. That’s where the continuous insulation layer comes in.
Why do inspectors check air sealing along with insulation R-values?
Thermal bridging isn’t the only way heat escapes. Air can also leak through gaps and holes, adding to the losses caused by the framing.
What climate zone is my project in for insulation code purposes?
Check the climate zone by county rather than assuming the city or state determines which one applies. County-level climate guidance helps builders confirm the correct zone for each project.
Steel studs create a thermal bridge through an insulated wall. Adding more cavity insulation doesn’t fix that bridge, but continuous insulation does.
That’s why the IECC continuous insulation requirement is a code-driven decision, not simply a performance upgrade. With steel-framed buildings, the entire assembly must address the framing.
Builders and developers planning steel-framed new construction or a multifamily project should work through the CI details before the walls are closed in. Contact Hudson Insulation to discuss a code-compliant insulation plan for your next steel-framed project.
References
Kosny, Jan, André O. Desjarlais, and Jeffrey E. Christian. “Thermal Performance of ‘Energy-Efficient’ Metal Stud Wall Systems.” Thermal Envelopes VI: Walls, Floors, Ceilings, Foundations I—Practices, Oak Ridge National Laboratory, 1995, web.ornl.gov/sci/buildings/conf-archive/1995%20B6%20papers/084_Kosny.pdf.
“Continuous Rigid Insulation Sheathing.” Building America Solution Center, Pacific Northwest National Laboratory / U.S. Department of Energy, basc.pnnl.gov/resource-guides/continuous-rigid-insulation-sheathing.
Baechler, Michael C., et al. Guide to Determining Climate Regions by County. Building America Best Practices Series, vol. 7.3, Pacific Northwest National Laboratory / U.S. Department of Energy, Aug. 2015, www.energy.gov/sites/prod/files/2015/10/f27/ba_climate_region_guide_7.3.pdf.