Timber vs Steel Beam Calculator — Material Comparison Guide

Quick access:

• Timber vs steel: head-to-head comparison
• When to use timber beams
• When to use steel beams
• Decision framework
• Span and capacity comparison
• Cost comparison
• Fire resistance comparison
• Frequently asked questions
• Try the calculators

Timber vs steel: head-to-head comparison

When to use timber beams

Timber beams are the right choice when:

Short to moderate spans (10-25 ft)

For residential and light commercial floors with spans under 25 ft, timber beams are cost-effective and readily available. A 4x12 Southern Pine No. 2 beam can span approximately 18 ft under typical floor loading. For spans above 20 ft, glulam beams (glued laminated timber) become necessary for sawn lumber applications.

Light to moderate loading

Timber excels when dead loads are low (10-15 psf) and live loads are moderate (40 psf residential, 50 psf office). For heavy loads (100+ psf assembly, library stacking, or industrial), steel is typically more efficient.

Fast construction with field modifications

Timber beams can be cut, drilled, and notched in the field with simple tools. This is valuable for renovation projects, complex roof geometries, and sites where fabricated steel delivery times are long.

Aesthetic exposed structure

Exposed timber beams provide a warm, natural appearance that is architecturally desirable for:

• Open-plan offices
• Retail and hospitality spaces
• Educational buildings
• Worship facilities
• Residential great rooms

Sustainability goals

Timber is a renewable resource that stores carbon. A cubic meter of timber stores approximately 1 ton of CO2. Cross-laminated timber (CLT) and glulam are increasingly used in mass timber structures that compete with steel in mid-rise construction.

When to use steel beams

Steel beams are the right choice when:

Long spans (25-60 ft)

For spans above 25 ft, steel W-shapes become more efficient than timber. A W24x55 can span 30-35 ft under typical office loading. At spans above 40 ft, steel is almost always the most economical structural option.

Heavy loads

Steel handles high loads with smaller sections. A steel beam at 50 ksi yield strength has approximately 25-50 times the bending capacity per unit area of sawn lumber. For industrial floors, parking structures, and high-rise buildings, steel is the standard.

Strict deflection limits

Steel has a consistent, predictable modulus of elasticity (E = 29,000 ksi vs. timber E = 1.1-1.9e6 ksi). For floors requiring L/480 or L/600 (laboratories, operating rooms, precision manufacturing), steel beams provide the stiffness needed without the depth penalty of timber.

Fire-rated assemblies

While steel requires fireproofing, the fire resistance is predictable and can be engineered to any rating. Spray-applied fireproofing (SFRM), intumescent coatings, and membrane protection (suspended ceilings) are standard, tested assemblies. Timber char calculations are also codified but require larger sections to achieve the same fire rating.

Connection to existing steel

In steel-framed buildings, adding a new steel beam is straightforward with bolted connections. Adding a timber beam to a steel frame requires special connection details (hangers, bearing seats, slip connections).

Multi-story construction

For buildings above 3 stories, steel framing is typically more economical than timber due to:

• Lower floor-to-floor height (shallower beams)
• Faster erection cycle (3-4 days per floor vs. 5-7 for timber)
• Better dimensional stability over time
• Prefabricated connections reduce field labor

Decision framework for beam material selection

Use this flow chart to decide between timber and steel:

1. Span required

   • Less than 20 ft: Timber is competitive
   • 20-30 ft: Either (compare cost and fire requirements)
   • 30-60 ft: Steel typically more economical
   • Above 60 ft: Steel or steel trusses

2. Load intensity

   • Total load below 100 psf: Timber is viable
   • Total load 100-200 psf: Steel usually more efficient
   • Total load above 200 psf: Steel is required

3. Deflection limit

   • L/360 or L/240: Either material works
   • L/480 or stricter: Steel preferred (consistent E)

4. Fire rating required

   • 1 hour or less: Either material (timber by char, steel by SFRM)
   • 2 hours: Steel with SFRM or timber by char (oversize section)
   • 3+ hours: Steel with SFRM (thicker coating)

5. Architectural exposure

   • Exposed: Timber (warm appearance) or steel (industrial aesthetic)
   • Concealed: Either (cost-based decision)

6. Construction schedule

   • Fast (6-8 week fabrication): Timber (readily available)
   • Very fast (4 weeks): Timber or light-gage steel
   • Normal (8-12 week fabrication): Steel

Span and capacity comparison

Equivalent beam sizes (residential floor, 40 psf LL, 15 psf DL, 8 ft spacing, L/360)

Notes:

• Timber sections are nominal dimensions (actual: 3.5 x 11.25 for 4x12)
• Steel sections shown are the minimum weight that meets both strength and deflection
• Glulam beams require lateral bracing at 24 in OC for compression edge
• All spans assume simple support conditions

Key observations

• At 16 ft span: Steel is 8 lb/ft (W8x13), timber is 10.5 lb/ft (4x10 at 35 pcf). Both are light.
• At 24 ft span: Steel is 22 lb/ft (W12x22), glulam is 28.5 lb/ft. Steel beam depth is 12 in vs glulam 13.5 in.
• At 32 ft span: Steel is 31 lb/ft (W16x31, 16 in deep). Glulam is 47 lb/ft (6.75x18, 18 in deep). Steel is 34% lighter and 2 in shallower.

Steel becomes increasingly efficient relative to timber as spans increase.

Cost comparison

Relative cost per linear foot (material only, 2026 estimates)

Total installed cost factors

Timber advantages:

• No fireproofing cost in many applications (1-hr by char calculation)
• Field cuts and modifications are simple
• Connection hardware is inexpensive (joist hangers, bolts)

Steel advantages:

• Faster erection (reduces crane/crew time)
• Smaller sections reduce shipping cost
• Consistent quality (fabricated in controlled environment)
• No moisture-related delays (no acclimation period)

Rule of thumb: Below 20 ft span, timber is typically 10-20% less expensive installed. Above 25 ft, steel is typically 15-30% less expensive installed.

Fire resistance comparison

Timber fire design

Timber beams achieve fire resistance through charring. Per NDS Chapter 16 and the National Design Specification for Wood Construction:

• Char rate: 1.5 in/hour (unprotected, sawn lumber and glulam)
• Effective char depth: 1.5 x t_required (for 1 hour: 1.5 in per exposed face)
• Remaining section must carry the design loads at increased stress (typically 2.85 x allowable for fire)
• 1-hr rating: 4x10 may be adequate; 2-hr rating: 6x12 or larger

Timber has inherent fire resistance because the char layer insulates the unburned interior. With proper detailing and oversizing, timber can achieve 1-2 hour ratings without additional fireproofing.

Steel fire design

Steel beams lose strength rapidly above 800F. Per AISC 360 Appendix 4:

• Unprotected steel: 15-30 minute rating (exposed W-shape)
• Spray-applied fire resistive material (SFRM): 1-4 hour rating
• Intumescent coating: 1-2 hour rating (thin-film, aesthetic)
• Membrane protection (suspended ceiling): 1-2 hour rating
• Concrete encasement: 3-4 hour rating

Comparison at 1-hour rating

Frequently asked questions

Which is stronger, steel or timber for beam applications?

Steel is significantly stronger than timber on a per-unit-area basis. A992 steel has a yield strength of 50 ksi, while Douglas Fir No. 2 has an allowable bending stress of 900 psi (about 1.8 ksi at ultimate). Steel is approximately 25-30 times stronger per square inch of cross-section. However, timber sections are often larger, partially compensating for the lower material strength.

Is timber more sustainable than steel?

Timber is renewable and stores carbon (approximately 1 ton CO2 per cubic meter). However, North American steel is 70-90% recycled content and is fully recyclable. A cradle-to-grave life cycle assessment (LCA) should consider: timber involves forestry management, transportation of bulky sections, and end-of-life disposal (landfill or incineration vs. recycling). A well-designed building in either material can achieve LEED certification. Mass timber structures are gaining traction as a low-carbon alternative to steel for mid-rise buildings.

Can I use the timber beam calculator for glulam beams?

Yes. The Wood Timber Calculator supports glulam beams with appropriate design values (Fb, E, Fv, Fc_perp) per the AITC 117 standard. Glulam beams are specified by a combination symbol like 24F-1.8E, where 24F means Fb = 2,400 psi and 1.8E means E = 1.8 x 10⁶ psi. The calculator adjusts these values for size factor, load duration, and wet service.

What is the maximum span for a 6x12 timber beam?

A 6x12 Douglas Fir No. 2 beam under typical residential floor loading (40 psf LL, 15 psf DL, 8 ft spacing) can span approximately 22-24 ft for L/360 deflection limit. The same beam in glulam (24F-1.8E) can span approximately 28-30 ft. For comparison, a W12x22 steel beam spans the same distance at 22 lb/ft with a 12 in section depth.

How do I detail connections between steel and timber beams?

Steel-to-timber connections typically use: (1) Bearing seats — a steel angle or plate welded to the steel beam to support the timber beam end. (2) Bolted connections — steel bolts through the timber beam into a steel bracket. (3) Joist hangers — face-mount hangers nailed to timber and bolted/welded to steel. (4) Slip connections — slotted holes allow timber shrinkage without splitting. All connections must account for timber shrinkage perpendicular to grain, which can cause 3-5% reduction in thickness over time.

Try the calculators

Use the free calculators to compare timber and steel beam designs:

• Timber: Wood Timber Calculator — design sawn lumber, glulam, LVL, and PSL beams per NDS 2018
• Steel: Beam Capacity Calculator — design W-shapes, UB, IPE sections per AISC 360, AS 4100, EN 1993
• Beam Deflection: Beam Deflection Calculator — compare deflection for both materials
• Beam Span: Beam Span Calculator — span tables for both materials

For reference:

• Timber Beam Reference — NDS wood beam design guide
• Beam Design Guide — steel beam design workflow
• Deflection Limits — allowable deflection by building use
• How to Verify Calculations — verification procedures

Disclaimer

This guide is for educational and reference use only. It does not constitute professional engineering advice. All design values must be verified against the governing building code, project specification, and applicable design standards. The Steel Calculator disclaims liability for any loss, damage, or injury arising from the use of this information. Always engage a licensed structural engineer for beam design on actual projects.

See Also

• Beam Capacity Calculator
• Beam Deflection Calculator
• Steel Beam Sizes Reference
• Beam Design Guide
• Beam Span Reference