Best Alternatives to Traditional RSJ Beams – Modern Options for 2026

While traditional RSJ steel beams remain the standard for load-bearing applications, several alternatives offer advantages in specific situations. From engineered timber products to advanced composite systems, modern construction provides numerous options. This comprehensive guide explores alternatives to conventional RSJ beams, comparing costs, performance, and ideal applications for 2026.

Why Consider Alternatives?

Reasons to explore RSJ alternatives:

• Environmental concerns (lower carbon footprint)
• Aesthetic requirements (exposed beams, specific appearance)
• Fire resistance without additional protection
• Cost considerations in high steel-price environments
• Thermal performance (reducing thermal bridging)
• Specific load conditions (better suited alternatives)
• Planning restrictions (conservation areas, listed buildings)

Alternative Options Overview

1. Engineered Timber Products

LVL (Laminated Veneer Lumber)

• Cost: £18-35/m
• Strength: 60-75% of equivalent steel
• Carbon: Very low (sequestered)

Glulam (Glued Laminated Timber)

• Cost: £40-80/m
• Strength: 50-70% of equivalent steel
• Carbon: Very low

CLT (Cross-Laminated Timber)

• Cost: £280-450/m³ (panel product)
• Strength: Excellent for slabs/walls
• Carbon: Negative (carbon sink)

2. Steel Alternatives

Box Sections (RHS/SHS)

• Cost: Similar to RSJ
• Strength: Comparable, better torsion resistance
• Application: Columns, specific architectural needs

Cellular Beams

• Cost: +30-60% vs standard RSJ
• Strength: Lighter for same capacity (holes in web)
• Application: Long spans, services integration

Stainless Steel

• Cost: +200-400% vs carbon steel
• Strength: Comparable
• Application: Corrosive environments, architectural

3. Concrete Solutions

Pre-cast Concrete Lintels

• Cost: £15-80 depending on size
• Strength: Limited vs RSJ
• Application: Light loads, short spans

Pre-stressed Concrete Beams

• Cost: £60-150/m
• Strength: Excellent for longer spans
• Application: Commercial, specific residential

4. Composite Systems

Flitch Beams (Steel-Timber-Steel)

• Cost: +20-40% vs pure steel
• Strength: Between timber and steel
• Application: Period properties, hybrid needs

Pultruded FRP (Fiber Reinforced Polymer)

• Cost: +80-150% vs steel
• Strength: Good strength-to-weight
• Application: Specialized (marine, chemical exposure)

Detailed Comparison: Engineered Timber

LVL (Laminated Veneer Lumber)

What it is:

• Thin wood veneers glued with grain parallel
• Manufactured in controlled factory
• Consistent properties (no knots/defects)
• Available sizes: 45-90mm thick, 200-600mm deep

Advantages:

• Lighter weight: 420kg/m³ vs steel 7,850kg/m³
• Lower carbon: ~-50 kg CO2e vs steel +230 kg CO2e typical beam
• Good fire performance: Chars predictably, no sudden failure
• Easy to work: Standard carpentry tools
• No thermal bridging: Better insulation
• Competitive cost: Often 10-30% cheaper than steel installed

Disadvantages:

• Larger sections needed: 1.5-2× depth vs steel for equivalent capacity
• Moisture sensitive: Must be protected, not outdoor use
• Lower stiffness: Greater deflection under load
• Load limitations: Not suitable for very heavy loads

Typical applications:

• Short-medium spans (3-6m)
• Residential floors
• Light commercial
• Exposed ceiling aesthetics

Cost example (4m knockthrough, 80 kN load):

• LVL 360×90mm: £28/m × 4.3m = £120
• vs RSJ 203×133×30: £72/m × 4.3m = £310
• Saving: £190 on material

BUT engineer must verify LVL adequate for specific loads!

Glulam (Glued Laminated Timber)

What it is:

• Dimension lumber boards glued in layers
• Can be curved/shaped
• Large sections possible (up to 2m+ depth)
• Beautiful appearance when exposed

Advantages:

• Architectural beauty: Natural wood appearance
• Sustainability: Renewable, carbon negative
• Versatile shapes: Curved beams possible
• Fire performance: Excellent (chars slowly)
• Large spans possible: Up to 30m+ for commercial

Disadvantages:

• Premium cost: 2-3× steel for equivalent capacity
• Specialist supply: Not all suppliers stock
• Moisture protection essential: Indoor only unless treated
• Connections complex: Requires specialist fixings

Typical applications:

• Architectural features (exposed beams)
• Churches, halls, large open spaces
• Eco-builds prioritizing sustainability
• Where appearance as important as structure

Cost example (4m beam, 80 kN):

• Glulam 360×140mm: £65/m × 4.3m = £280
• vs RSJ: £310
• Similar cost, much larger section, beautiful appearance

Choose when: Aesthetics justify larger beam size

CLT (Cross-Laminated Timber)

What it is:

• Boards laminated crosswise (like plywood but thicker)
• Panel product (not beam)
• Very rigid, two-way spanning
• Typical thickness: 60-300mm

Applications:

• Floor/roof panels
• Load-bearing walls
• Whole-building systems
• NOT typically used for beams (panels instead)

Advantages:

• Carbon negative: Major environmental benefit
• Fast construction: Pre-fabricated panels
• Excellent performance: Strong in multiple directions

Cost: Competitive for whole-building systems, not direct RSJ alternative

Steel Alternative Sections

Box Sections (RHS - Rectangular Hollow Section)

What they are:

• Hollow rectangular steel tubes
• Equal strength all directions
• Sizes: 50×25mm to 500×300mm typical
• Wall thickness: 2.5-16mm

Compared to RSJ:

Factor	RHS Box	RSJ Beam
Bending (one axis)	Similar	Similar
Torsion resistance	Much better	Weaker
Weight	Lighter	Heavier
Appearance	Cleaner (if exposed)	Traditional
Cost	Similar	Slightly cheaper
Connections	More complex	Standard

Best application:

• Columns (vertical members)
• Exposed architectural beams
• Where torsion/twisting loads present
• Modern aesthetic preference

Cost: £55-95/m (comparable sizes to RSJ)

Cellular/Castellated Beams

What they are:

• Standard I-beams with holes cut in web
• Holes allow services (pipes, ducts) to pass through
• Lighter weight for equivalent capacity

Advantages:

• Services integration: Mechanical/electrical through beam
• Longer spans: 20-40% span increase possible
• Material efficiency: Lighter, less steel

Disadvantages:

• Higher cost: +30-60% vs standard RSJ (fabrication)
• Specialist supply: Must be custom made
• Design complexity: Engineer must analyze holes

Applications:

• Commercial buildings (services-heavy)
• Long-span residential (open plan)
• Where headroom critical (use depth for services)

Cost: £85-135/m (vs £65-85/m standard RSJ equivalent)

Only economical when span/services justify premium

Concrete Alternatives

Pre-cast Concrete Lintels

Standard residential lintels:

• Sizes: 100-215mm high, lengths to 4m
• Reinforced with steel bars internally
• Ready to install

vs RSJ:

Factor	Concrete Lintel	RSJ
Load capacity	Low-Medium	High
Cost	Very cheap (£15-80)	Moderate (£280-400)
Span capability	Short (<3.5m)	Long (6m+)
Weight	Heavy	Moderate
Fire resistance	Excellent	Poor (needs protection)
Thermal bridging	Low	High

Use concrete when:

• Light loads only (masonry, roof)
• Short spans (<3m)
• No floor loads
• Fire resistance priority
• Budget very tight

Don’t use when:

• Floor/structural loads above
• Spans >3.5m
• Room above opening

Cost saving: £200-300 vs RSJ but LIMITED application scope

Pre-stressed Concrete Beams

What they are:

• Factory-manufactured concrete beams
• Steel tendons pre-tensioned
• Very strong for weight
• Sizes: 150-600mm deep, spans to 15m+

Advantages:

• Long spans: Compete with steel for 8-12m spans
• Fire resistant: No protection needed
• Durable: 100+ year lifespan, low maintenance
• Good appearance: Can be exposed if desired

Disadvantages:

• Heavy: Crane essential for installation
• Lead time: Often 4-6 weeks
• Less flexible: Difficult to modify after manufacture
• Connections complex: Need specialist details

Applications:

• Commercial construction
• Large residential (very wide openings)
• Multi-story concrete frame
• NOT typical domestic knockthrough (overkill and impractical)

Cost: £60-150/m depending on size

Use when: Commercial/large-scale projects, concrete frame building

Composite/Hybrid Solutions

Flitch Beams

Construction:

• Steel plate sandwiched between timber boards
• Bolted together in composite action
• Combines properties of both materials

Example: 200mm deep flitch

• 75mm timber - 8mm steel plate - 75mm timber
• Capacity: ~60-70% of pure steel
• Appearance: Timber (plate hidden)
• Cost: +20-40% vs pure steel

Advantages:

• Timber aesthetic: Exposed faces look like wood
• Better than pure timber: Steel core adds strength
• Fire performance: Better than exposed steel
• Period properties: Matches existing timber

Disadvantages:

• Fabrication cost: Custom assembly required
• Less efficient than pure steel: Heavier for capacity
• Connections tricky: Bolting through critical

Best use:

• Listed buildings (concealed steel acceptable)
• Where timber appearance desired but inadequate alone
• Conservation areas

Cost (4m beam): £380-480 vs £310 pure steel

Fiber Reinforced Polymer (FRP)

What it is:

• Glass or carbon fibers in polymer resin matrix
• Pultruded (pulled through die) sections
• I-beam shapes available

Advantages:

• Corrosion resistant: Total immunity to rust
• Very lightweight: 75-85% lighter than steel
• Non-conductive: Electrical/magnetic neutral

Disadvantages:

• Very expensive: +80-200% vs steel
• Low stiffness: Deflection often limits capacity
• UV sensitive: Degradation in sunlight (needs coating)
• Connection difficulties: Can’t weld, bolting critical
• Limited fire performance: Resin degrades in heat

Applications:

• Chemical plants (corrosive atmospheres)
• Marine structures
• MRI rooms (non-magnetic)
• Specialized only

NOT appropriate for typical residential use (cost unjustifiable)

Cost: £150-250/m vs £65-85/m steel

Decision Framework

Choose LVL/Glulam When:

• Span <6m
• Residential floor loads (not heavy commercial)
• Indoor application (dry environment)
• Environmental sustainability priority
• Fire resistance desired without boxing
• Exposed beam aesthetics acceptable
• Cost-competitive or cheaper than steel

Typical saving: 10-40% vs steel installed

Choose Concrete Lintel When:

• Span <3m
• Masonry/roof loads only (NO floors above)
• Budget very constrained
• Fire resistance essential
• Standard door/window opening

Typical saving: £200-350 vs RSJ

Choose Steel Box Section When:

• Column application
• Torsion loads present
• Modern architectural aesthetic
• Exposed/visible beam (clean appearance)

Cost: Similar to RSJ

Choose Cellular Beam When:

• Long span (8m+)
• Services must pass through beam
• Commercial application justifies premium
• Headroom at absolute premium

Cost: +30-60% vs RSJ

Stick with Traditional RSJ When:

• Heavy floor/structural loads
• Long spans (>6m)
• Space constraints (slim profile needed)
• Standard proven solution adequate
• Cost-effectiveness priority
• Builder familiarity important

Most reliable, cost-effective for load-bearing alterations

Real Project Comparisons

Project 1: 3.5m knockthrough, single story garage (no room above)

Option A: RSJ 203×133×25

• Material: £245
• Install: £300
• Total: £545

Option B: Concrete lintel 150×140×4000mm

• Material: £65
• Install: £180
• Total: £245

Winner: Concrete (£300 saving), adequate for loads

---

Project 2: 5m knockthrough, bedroom above

Option A: RSJ 254×146×31

• Material: £395
• Install: £450
• Total: £845

Option B: LVL 400×90mm

• Material: £140
• Install: £320 (lighter, easier)
• Total: £460

Winner: LVL IF engineer confirms adequate (£385 saving + environmental benefit)

---

Project 3: 8m open-plan living, exposed beam aesthetic desired

Option A: RSJ 305×165×40 (boxed for fire protection)

• Material: £680
• Boxing: £180
• Install: £750 (crane)
• Total: £1,610

Option B: Glulam 520×160mm (exposed)

• Material: £1,040
• Install: £580
• Total: £1,620

Winner: Glulam (similar cost, beautiful exposed finish, sustainability)

Environmental Comparison

Carbon footprint (4m beam supporting 80 kN load):

Traditional steel RSJ:

• Embodied carbon: +232 kg CO2e
• Recyclability: 100%

LVL timber:

• Embodied carbon: -45 to +15 kg CO2e (carbon sequestered)
• Renewability: 100% (if FSC certified)

Glulam:

• Embodied carbon: -60 to +10 kg CO2e
• Renewability: 100%

Concrete:

• Embodied carbon: +180-220 kg CO2e (cement-intensive)
• Recyclability: Limited (aggregate only)

Environmental ranking:

1. Engineered timber (LVL/Glulam) - Best
2. Recycled-content steel - Good
3. Virgin steel - Moderate
4. Concrete - Poor

2026 trend: Timber alternatives increasingly popular for environmental reasons

Conclusion

Traditional RSJ steel beams remain optimal for most load-bearing applications, but alternatives offer advantages in specific scenarios:

Best alternatives by use case:

Light loads, short spans (<3m): Concrete lintels (£200-350 saving)

Medium loads, medium spans (3-6m), sustainability priority: LVL timber beams (10-40% cheaper, excellent carbon footprint)

Architectural/exposed beams: Glulam (similar cost to boxed steel, beautiful appearance)

Columns/modern aesthetic: Steel box sections (similar cost, cleaner look)

For typical residential knockthroughs with floor loads above: Traditional RSJ still most cost-effective and reliable choice

Key decision factors:

1. Structural engineer must approve alternative (never substitute without professional approval)
2. Consider total installed cost, not just material
3. Factor in long-term performance and maintenance
4. Balance cost, appearance, environmental impact, and performance

Always consult your structural engineer - they’ll recommend the optimal solution balancing all factors for your specific project.

Disclaimer: All structural alternatives must be designed and approved by a chartered structural engineer. This guide provides general comparison only and does not replace professional engineering design.