Cost & Financing

Steel vs. Wood Framing: A Complete Technical Comparison for Multifamily Construction

Cold-formed steel (CFS) framing qualifies as non-combustible under IBC Type IIA/IIB construction, eliminating the concrete podium wood framing requires above 4 stories. Wood framing costs less at 4 stories and below; the systems reach cost parity at 5 stories; and CFS becomes progressively cheaper at 6+ stories, driven by podium elimination and fire-retardant-treated lumber premiums that wood incurs at those heights.
  • 16-minute read
Who this article is for: Developers, architects, and structural engineers evaluating framing systems for 4–8 story multifamily projects.

Technical comparison of cold-formed steel and wood framing for 4–8 story multifamily construction, covering IBC construction types, structural performance, fire ratings, full-system cost analysis, and

IBC Construction Type Classifications

The most fundamental difference between CFS and wood framing for mid-rise construction is the IBC construction type classification each material enables. Cold-formed steel is classified as non-combustible per IBC 602.2 and ASTM E136, qualifying CFS-framed buildings for Type IIA and Type IIB construction.

Construction Type Max Stories (R-2, Sprinklered) Max Height (ft) Structural Frame Fire Rating CFS Bearing Wall Protection Required?
Type IIB 5 stories 75 ft 0 hours No — unprotected CFS permitted
Type IIA 5 stories 85 ft 1 hour Yes — UL H514 or equivalent required
Type IB 12 stories 180 ft 2 hours Yes — UL H505 or equivalent required

IBC §510.2 permits a single-story Type IA podium to support Type IIB above, enabling a total of 6 stories (1 podium + 5 Type IIB). IBC §510.4 permits a two-story Type IA podium enabling 7 stories total.

Wood framing is combustible. It qualifies for Type IIIA (1-hour) or Type IIIB (0-hour) with non-combustible exterior cladding, or Type VA/VB without it. The critical limitation: wood-framed buildings exceeding 4 stories require IBC §510 podium construction — a Type IA base structure onto which the wood-framed upper floors are placed. This podium requirement is the primary economic driver separating CFS and wood framing economics at 5+ stories.

Structural Performance Comparison

CFS structural members are designed per AISI S100 using the Effective Width Method or Direct Strength Method; steel yields at 33–50 ksi with modulus of elasticity at 29,500 ksi. Wood members are designed per NDS, with design values varying by species, grade, moisture condition, and load duration factor.

Property Cold-Formed Steel (CFS) Wood Framing (SPF #2)
Design Standard AISI S100 / S240 / S400 NDS 2018 / SDPWS 2021
Fabrication Tolerance ±1/8″ (CNC roll-forming) ±1/4″–3/8″ field tolerance
Moisture-Driven Shrinkage Negligible (inorganic material) 3–8% cross-grain shrinkage during drying
Biological Resistance Immune to termites, fungal decay, mold Susceptible — treatment required above 2 stories
Fire Classification Non-combustible per IBC 602.2 / ASTM E136 Combustible — ignites at 400–500°F

Wood framing shrinks cross-grain as it dries — typically 3–8% for SPF framing lumber installed at above-equilibrium moisture content. In a 5-story building with 2×10 floor framing at each level, accumulated shrinkage can reach 1–2 inches over building height, causing nail pops, drywall cracking at corners, plumbing binding, and elevator door alignment problems. CFS members maintain dimensional stability within ±1/8″ fabrication tolerance, produced by CNC roll-forming equipment to precise digital models.

Lateral force-resisting system design for CFS is governed by AISI S400, with hold-down forces and anchor rod specifications calculated per ASCE 7-22. Wood shear walls are designed per SDPWS 2021. Both systems deliver code-compliant lateral performance when properly engineered.

Fire Performance: Non-Combustible vs. Combustible Systems

CFS melts at approximately 2,700°F. Wood ignites at 400–500°F and contributes fuel load during a fire event — once gypsum board protection is breached in a wood-framed building, the structural frame itself becomes a fuel source. In a CFS-framed building, the structural frame is non-combustible per ASTM E136 and does not add to the fire’s fuel load once the gypsum assembly is compromised.

CFS construction achieves fire-resistance ratings through tested assemblies listed in the UL Fire Resistance Directory. Type IIB CFS construction requires zero hours of structural frame fire protection per IBC Table 601 — fire-rated assemblies are required only for occupancy separations, floor/ceiling assemblies, corridor walls, and shaft enclosures, requirements that apply equally to wood construction at the same building heights.

UL Design Fire Rating Application
H505 2-hour CFS load-bearing wall — Type IIA or occupancy separation
H514 1-hour CFS load-bearing wall — Type IIA structural frame protection
L541 1-hour CFS floor/ceiling assembly
G602 3-hour CFS floor/ceiling — eliminates structural concrete topping
M527 1-hour CFS non-load-bearing corridor wall
N501 / D902 2-hour CFS shaft wall and area separation wall

UL Design G602 achieves a 3-hour ASTM E119 floor/ceiling rating without structural steel deck or concrete topping slab, using fiberglass-reinforced cement panels over CFS C-joists. The assembly replaces a composite deck/concrete floor weighing 50–65 psf with an assembly weighing only 12–18 psf — reducing supporting member sizes and foundation demands.

Note: Acoustic values and fire ratings are assembly-specific. Substituting any material component — gypsum type, screw size or spacing, stud gauge, or resilient channel specification — voids the UL listing. Always verify all assembly components against UL Product iQ prior to specification and submittal.

Cost Analysis: The Full-System Economic Picture

The persistent misconception that CFS is significantly more expensive than wood framing is based on material unit cost comparisons that exclude the podium requirement, FRT lumber premiums, schedule value, and insurance differential that govern total project economics at 5+ stories.

Building Height Wood Framing Cost ($/SF) CFS Framing Cost ($/SF) Cost Differential
4 Stories $14.50–$16.50 $24.00–$26.00 Wood saves ~$9–10/SF
5 Stories $23.50–$29.50 (Type IIIB + podium) $24.50–$26.50 Cost parity range
6 Stories $31.00–$37.00 (+ FRT + podium) $26.00–$28.00 CFS saves ~$13.42/SF
7 Stories $38.00–$46.00 (+ FRT + podium) $27.00–$29.00 CFS saves ~$21.11/SF

Above 4 stories, wood-framed buildings classified as Type IIIA require fire-retardant-treated (FRT) lumber throughout the structural frame, which imposes costs beyond material price: structural capacity reduction (bending design values drop 10–25%, requiring larger members), stainless steel fastener upgrades ($0.25–$0.40/SF), extended procurement lead time (6–12 weeks vs. 4–6 weeks), and additional special inspection ($3,000–$5,000 per project). Total FRT impact on a 60,000 SF 6-story building is estimated at $294,000–$465,000 in additional framing costs. CFS uses standard ASTM A1003 Grade 33/50 galvanized coil at all building heights — no height-driven material substitution.

The single largest cost driver distinguishing CFS from wood at 5+ stories is the Type IA concrete podium, which typically adds $12–15/SF in construction cost plus 8–12 weeks of formwork, placement, and cure cycle before wood framing can begin. At a carrying cost of $50,000–$150,000 per month, that schedule impact alone can represent $100,000–$1.5M in financing cost not captured in the framing cost comparison. CFS-framed buildings at 5+ stories require no podium under Type IIB or Type IIA.

Thermal Performance and Schedule Performance

Steel’s thermal conductivity (25–50 W/m·K) is significantly higher than wood’s (0.12 W/m·K), creating heat flow pathways through CFS stud flanges. The mitigation is continuous exterior insulation (ci) applied outboard of the framing, which physically interrupts the thermal bridge at each stud flange.

CFS Wall Assembly Cavity Insulation Continuous Insulation Effective U-Factor
CFS — no continuous insulation R-13 batt None ~U-0.125 (does not meet code)
CFS — IBC 2021 base code R-13 batt R-7.5 polyiso ~U-0.064 ✓
CFS — MA Stretch Code R-19 batt R-15 polyiso ~U-0.051 ✓

Massachusetts 780 CMR / 225 CMR 23 Stretch Code requires a minimum of R-13 cavity + R-7.5 continuous insulation for CFS exterior walls in Climate Zone 5A. NFPA 285 testing per 780 CMR 1403 is required for all exterior wall assemblies on buildings over 40 feet.

Prefabricated CFS panel systems replace the traditional sequential construction workflow with a parallel one, where panel fabrication runs concurrently with foundation construction. Every project begins with LOD 400 BIM coordination at contract execution, resolving conflicts between framing, mechanical, electrical, and plumbing before fabrication begins. For a 5-story, 80-unit multifamily project, panelized CFS completes structural framing in 8–12 weeks compared to 16–22 weeks for equivalent wood-frame construction including the podium phase — delivering construction loan interest savings (approximately $43,000 per week on a $30M loan at 7.5%) and general conditions reduction (approximately $70,000–$100,000 per week).

Frequently Asked Questions

At what building height does cold-formed steel become more cost-effective than wood framing?

Under RSMeans 2024 Boston market data, wood framing is approximately $9–10/SF cheaper than CFS at 4 stories and below. The two systems reach cost parity at 5 stories. At 6 stories, CFS saves approximately $13.42/SF; at 7 stories, $21.11/SF. The crossover point is driven by the concrete podium requirement that wood framing triggers at 5+ stories and the FRT lumber premium imposed at Type IIIA construction.

Why does wood framing require a concrete podium above 4 stories?

IBC §510 requires a Type IA podium (concrete or structural steel) to support combustible wood framing when building height exceeds the 4-story limit for Type VA construction. The podium adds $12–15/SF in construction cost plus 8–12 weeks of formwork, placement, and cure cycle to the project schedule. CFS framing eliminates this requirement entirely because the entire building is non-combustible.

What is FRT lumber and why does it add cost at 6+ stories?

FRT (fire-retardant-treated) lumber is required by IBC Type IIIA construction for buildings 6+ stories where wood framing is permitted. The chemical treatment reduces bending design values by 10–25%, requiring larger member sizes. Stainless steel fasteners are also required. Procurement lead time extends to 6–12 weeks, and additional inspection adds $3,000–$5,000 per project. Total FRT impact on a 60,000 SF 6-story building runs $294,000–$465,000 in additional framing costs.

Does CFS framing comply with Massachusetts 780 CMR and the Stretch Energy Code?

Yes. CFS-framed multifamily buildings comply with both 780 CMR base code and the Massachusetts Stretch Energy Code (225 CMR 23). Stretch Code compliance in Climate Zone 5A requires R-13 cavity + R-7.5 continuous insulation minimum for CFS exterior walls; an upgraded R-19 cavity + R-15 continuous insulation assembly delivers approximately U-0.051.

References

  • International Code Council — IBC 2021: International Building Code, Section 510, Section 602, Section 713, Section 903.3.1.1; Tables 504.3, 504.4, 601, 508.4, 1020.1.
  • Board of Building Regulations and Standards — 780 CMR: Massachusetts State Building Code; 225 CMR 23 Stretch Energy Code.
  • American Iron and Steel Institute — AISI S100-16, AISI S240-20, AISI S400-20.
  • American Wood Council — NDS 2018; SDPWS 2021.
  • American Society of Civil Engineers — ASCE 7-22.
  • ASTM International — ASTM E119, ASTM E136, ASTM A1003.
  • National Fire Protection Association — NFPA 13; NFPA 285.
  • ASHRAE — ASHRAE 90.1, Appendix A.
  • Underwriters Laboratories — UL Fire Resistance Directory and UL Product iQ.
  • RSMeans — Building Construction Cost Data, 2024 Edition (Boston market).

Ready to Compare Steel vs. Wood for Your Project?

To discuss CFS vs. wood framing economics, IBC Type IIB compliance, or panelized fabrication coordination for your mid-rise multifamily project, contact our engineering team at nick@aacsteel.com or 617-560-0349. AAC Steel will produce a project-specific cost and schedule comparison using your floor plan, unit count, height, and financing terms.

Cost data referenced in this article reflects RSMeans 2024 published values (Boston market), SFIA industry data, and AAC Steel project cost database experience in the New England market. Actual project costs vary based on site conditions, design complexity, local labor rates, market conditions, and material price fluctuations. Lumber pricing has experienced 300% historical volatility — verify current pricing against RSMeans quarterly updates. Consult AAC Steel directly for project-specific analysis.

About AAC Steel

AAC Steel is a cold-formed steel (CFS) framing company headquartered in Franklin, MA, founded by engineers and builders with two decades of experience on Northeast jobsites. The company designs, fabricates, and installs precision CFS structural systems — including PE-stamped engineering, BIM and shop drawings, and panelized fabrication — for 5+ story multifamily developments across Massachusetts, Rhode Island, and Connecticut.

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