16-Inch vs. 24-Inch On-Center Framing: What It Means for Energy Efficiency and HERS Ratings in Massachusetts
Overview
Most new homes in Massachusetts use 16-inch on-center (OC) framing by default for walls, roofs, and floors. However, building science experts and energy modelers are revisiting the benefits of 24-inch OC framing—a strategy that can provide structural, thermal, and cost benefits when implemented properly.
Let's explore why the industry moved from 24" to 16" OC, how 24" spacing reduces thermal bridging, and the impacts across walls, roofs, and floors on energy efficiency and HERS ratings under the 2021 IECC and Massachusetts Stretch Code.
The Shift from 24-Inch to 16-Inch Spacing
Historically, 24" OC framing was standard in many applications, especially in energy-conscious builds. Over time, 16" OC became the norm due to:
Compatibility with drywall and sheathing products rated for 16" spans
Structural codes emphasizing tighter framing for load support
Builder preference and industry momentum
Perceptions of greater rigidity and durability
While 16" spacing has advantages, it introduces more framing members, increasing material use and thermal bridging.
Thermal Bridging and Its Impact on HERS Scores
Studs in framing assemblies conduct heat more readily than insulation, causing thermal bridging. More framing members mean more heat flow through the envelope.
With 16" OC framing:
The framing fraction (percentage of wall area made up by studs) can reach ~25%
This lowers the effective R-value of assemblies
Increases heating and cooling loads
Leads to higher HERS scores
How 24-Inch OC Framing Improves Walls, Roofs, and Floors
Walls
Reducing stud density from 16" to 24" OC lowers the framing fraction, boosting effective wall insulation value. Combined with continuous exterior insulation, it dramatically reduces thermal bridging.
Roofs
For roof framing (rafters or trusses), 24" OC spacing is common and often preferred for cost and material savings. Using 24" OC roof framing with proper insulation strategies—such as continuous insulation or dense-packed cavities—helps maintain envelope continuity and improve HERS scores.
Floors
Floor joists are typically spaced at 16" or 24" OC depending on structural requirements and span. Using 24" OC spacing reduces framing material and thermal bridging in floor assemblies but must be carefully engineered to avoid deflection and structural issues.
When to Consider 24" OC Framing
24" OC framing is ideal when:
Structural spans and loads allow for wider spacing (consult a structural engineer)
Using advanced framing techniques (single top plates, insulated corners, ladder blocking)
Sheathing and drywall products rated for 24" spans are specified
Aiming to reduce material costs and waste
Seeking to improve HERS scores by reducing thermal bridging
Incorporating continuous insulation on walls or roofs
Best Practices for Energy-Efficient Framing
Pair 24" OC framing with continuous exterior insulation for walls and roofs
Use appropriate sheathing and drywall thickness rated for wider spans (e.g., 5/8")
Incorporate advanced framing details to maximize insulation performance
Confirm structural adequacy with engineers before design changes
Engage your HERS rater early for accurate modeling and optimization
FAQs
Is 24" OC framing structurally sound?
Yes, with 2x6 framing, proper sheathing, and engineering, 24" spacing meets code and maintains strength.
Will 24" OC framing lower material costs?
Yes, fewer studs and joists reduce lumber use and waste, saving money.
Is 24" OC allowed under Massachusetts code?
Yes, 2021 IRC and IECC codes permit 24" spacing when engineered correctly.
How does framing spacing impact my HERS score?
Lower framing fraction reduces thermal bridging, improving insulation effectiveness and lowering your HERS rating.
Final Thoughts
Reconsidering framing spacing offers a real opportunity to improve energy efficiency and reduce costs in Massachusetts homes. 24" OC framing, when executed correctly across walls, roofs, and floors, can help meet Stretch Code requirements and lower HERS scores.
Discuss framing options with your design and building team early to maximize benefits.
Need Help Navigating Energy Code and Framing Choices?
Spectrum Energy specializes in HERS ratings, energy modeling, and code compliance in Massachusetts. Contact us to optimize your framing and insulation strategies for the best performance.
