Structural Engineer Costs for RSJ Calculations UK 2026

Structural engineer involvement is legally mandatory for all RSJ beam installations, but many homeowners are unclear about costs, what’s included, and how to find the right engineer. This comprehensive guide covers typical fees for 2026, what you get for your money, cost factors, and strategies for obtaining best value.

Typical Costs 2026

By Project Type

Simple domestic knockthrough (single beam):

• Fee: £350-600
• Site visit, calculations, detail drawings
• Building Control submission support
• 1-2 week turnaround

Medium complexity (loft conversion, 2-3 beams):

• Fee: £500-900
• Site survey, multiple beam calculations
• Floor strengthening assessment
• Detailed drawings and specifications

Large project (extension, multiple floors):

• Fee: £800-1,800+
• Comprehensive structural design
• Foundation design
• Multiple beam/column calculations
• Ongoing site support

Hourly rate (if itemized):

• £80-150/hour depending on experience and location
• London/Southeast: £120-150/hour typical
• Regional: £80-120/hour

What’s Included in Typical Fee

Standard knockthrough calculation package (£400-550):

1. Initial consultation:

• Phone/email discussion of project
• Advise on feasibility
• Outline requirements

2. Site visit:

• 30-90 minutes on site
• Measure existing structure
• Photograph conditions
• Identify constraints
• Discuss client requirements

3. Structural calculations:

• Load analysis (dead + live loads)
• Beam size determination
• Pad stone requirements
• Temporary works advice
• Safety factors and checks
• 10-20 page calculation document

4. Detail drawings:

• Beam layout plan
• Section details showing beam, supports, connections
• Specifications (beam grade, size, fixings)
• Building Control submission quality

5. Building Control support:

• Cover letter for submission
• Respond to Building Control queries
• Technical clarification if needed

Additional services (usually extra charge):

• Multiple site visits: £100-200 each
• Site attendance during installation: £150-300
• Design changes/revisions: £80-200
• Party Wall Act documentation: £200-500

Cost Factors

1. Project Complexity

Simple (lower cost):

• Single beam
• Standard residential loads
• Straightforward support conditions
• No unusual features

Complex (higher cost):

• Multiple beams
• Transfer structures
• Point loads
• Existing structural issues
• Conservation/listed building constraints

Price impact: 50-150% variation

2. Engineer Experience/Qualifications

Newly chartered (CEng, IStructE):

• Fee: £350-500 for simple work
• Adequate for standard projects
• May take longer, more cautious designs

Experienced (10+ years):

• Fee: £450-700
• Efficient, optimal designs
• Familiar with Building Control requirements

Principal/Director level:

• Fee: £600-900+
• Complex projects
• Specialist knowledge
• Professional indemnity confidence

3. Location

London/Southeast:

• +30-50% premium vs. national average
• Typical knockthrough: £500-700

Major cities (Manchester, Birmingham, Leeds):

• +15-25% premium
• Typical knockthrough: £420-600

Regional/rural:

• Base rate
• Typical knockthrough: £350-500

Remote areas:

• May struggle to find local engineers
• Travel costs if using distant engineer: +£150-300

4. Turnaround Time

Standard (2-3 weeks):

• Normal fee structure

Urgent (<1 week):

• +25-50% rush fee
• Subject to engineer availability

Very urgent (48-72 hours):

• +50-100% premium
• Rarely available for complex work

5. Professional Indemnity Insurance Level

Standard (£1-2 million):

• Normal fee

High (£5-10 million):

• Required for large/commercial projects
• May increase fee 10-20%
• More rigorous checking

Finding a Structural Engineer

Options for Finding Engineers

1. Institution of Structural Engineers (IStructE) Directory:

• www.istructe.org/find-an-engineer
• Search by postcode
• Verified chartered members
• Best for: Finding qualified local engineers

2. Recommendations:

• Ask builders, architects
• Neighbors who’ve done similar work
• Online reviews (Google, Checkatrade)
• Best for: Finding engineers familiar with local Building Control

3. Online platforms:

• Bark.co.uk, MyBuilder, etc.
• Get multiple quotes
• Check reviews carefully
• Best for: Price comparison

4. Architect referral:

• If using architect, they’ll recommend
• Often established working relationship
• Best for: Complex/design-led projects

Vetting Your Engineer

Essential checks:

1. Professional registration:

• Chartered Engineer (CEng)
• Member IStructE (MIStructE) or ICE (MICE)
• Verify on institution website

2. Insurance:

• Professional indemnity £1m+ minimum
• Public liability insurance
• Ask for certificate

3. Experience:

• Domestic structural work
• Similar projects to yours
• Local Building Control familiarity

4. References:

• Previous client testimonials
• Recent projects
• Building Control relationships

Red flags:

• Not chartered/qualified
• No PI insurance
• Unwilling to provide references
• Unusually cheap (£200-300 for complex work)

Getting Best Value

1. Clear Brief

Provide engineer with:

• Detailed description of work
• Existing drawings if available
• Photos of site
• Access to property for measurement
• Timeline requirements

Clearer brief = more accurate quote, less revisions

2. Competitive Quotes

Get 2-3 quotes:

• Compare scope (what’s included)
• Not just price
• Interview engineers (phone/video)

Beware lowest quote:

• May be inexperienced
• May exclude essential services
• Can cost more long-term (design changes, Building Control rejections)

Sweet spot: Middle quote with best qualifications/references

3. Package Negotiation

If doing multiple projects:

• “I’m planning knockthrough now, loft conversion next year”
• Negotiate package deal (10-20% discount possible)

4. Do Your Homework

Reduce engineer time:

• Measure opening size and wall thickness yourself
• Photograph extensively
• Note floor joist direction and spacing
• Research typical beam sizes (helps discussion)

Can save 0.5-1 hour of engineer time = £40-150

5. Timing

Off-peak months (Jan-Feb, July-Aug):

• Engineers less busy
• More negotiable on fee
• Faster turnaround

Peak (March-June, Sept-Nov):

• Higher demand
• Less flexibility
• Potential delays

What You Get (Tangible Deliverables)

For your £400-550, you receive:

1. Calculation pack (PDF):

• Typically 10-20 pages
• Shows all load calculations
• Beam selection justification
• Code compliance checks
• Engineer’s stamp and signature

2. Detail drawings (PDF or CAD):

• Usually 1-3 sheets A3/A4
• Plan view showing beam location
• Section details
• Padstone details
• Dimensioned and annotated

3. Specification:

• Beam size (e.g., 203×133×30 UB)
• Steel grade (S275/S355)
• Supports (padstone size, concrete grade)
• Installation notes
• Temporary works advice

4. Building Control letter:

• Cover letter for submission
• Summary of design
• Compliance statement

Value: These documents worth their weight in gold for:

• Legal compliance
• Building Control approval
• Builder pricing/installation
• Future property sales (proof of compliance)
• Insurance purposes

DIY vs. Professional Engineer

Can you DIY structural calculations?

Legally: No specific restriction on who performs calculations

Practically: Absolutely NOT recommended because:

1. Complexity:

• Requires understanding of:
  • Load paths and distribution
  • Material properties
  • Safety factors
  • Deflection limits
  • Code requirements (Eurocodes)
• University degree level knowledge

2. Liability:

• YOU liable if failure occurs
• Criminal prosecution possible
• Civil claims for damage/injury

3. Building Control:

• Will scrutinize non-professional calculations heavily
• Often reject, requiring professional anyway
• Wastes time and money

4. Insurance:

• Professional indemnity insurance essential
• Not available to non-professionals
• Your home insurance likely excludes DIY structural work

Online beam calculators:

• Useful for ballpark estimates only
• NOT substitute for full engineering
• Don’t account for all factors
• No liability protection

Verdict: ALWAYS use chartered structural engineer - £400-550 is cheapest insurance policy you’ll ever buy!

Structural Engineer vs. Architect

Common confusion: “Do I need architect or engineer?”

For RSJ installation:

• Structural engineer: ESSENTIAL (calculations, beam sizing)
• Architect: Optional (design, aesthetics, planning)

When you need both:

• Complex extensions, loft conversions
• Architect designs space, engineer ensures structure works
• Coordinate between them
• Total fees: Architect £800-2,000+ PLUS engineer £500-1,000+

When engineer alone sufficient:

• Simple knockthrough
• Garage conversion
• Basic beam installation
• No planning permission needed

Red Flags / Problem Engineers

Warning signs:

1. Produces calculations without site visit:

• Guessing dimensions/conditions
• Risky assumptions
• May oversize (expensive) or undersize (dangerous)

2. Very fast turnaround (<48 hours) for complex work:

• Likely not thorough
• May be template-based without project-specific analysis

3. Won’t engage with Building Control queries:

• “That’s your problem once I’ve done calcs”
• Should be part of service

4. Doesn’t carry PI insurance:

• Major red flag
• Leaves you exposed

5. Spec-only without calculations:

• “Use 254×146×31 for 4m span”
• No justification/documentation
• Building Control will reject

Typical Timeline

Week 1:

• Contact 2-3 engineers
• Receive quotes
• Select engineer

Week 2:

• Site visit scheduled
• Engineer measures, photographs

Week 3:

• Calculations performed
• Drawings produced

Week 4:

• Documents delivered
• Review with engineer
• Submit to Building Control

Total: 3-4 weeks from first contact to Building Control submission

Add buffer for:

• Holiday periods
• Engineer workload
• Your availability for site visit

Case Study Costs

Project 1: Simple knockthrough (3.8m, one floor above)

• Engineer fee: £420
• Deliverables: 12-page calcs, 2 drawings, spec
• Beam specified: 203×133×30
• Building Control approved first time
• Cost per meter of opening: £111/m

Project 2: Loft conversion (ridge beam + floor beams)

• Engineer fee: £780
• Deliverables: 28-page calcs, 4 drawings, spec
• Multiple beams specified
• Two site visits included
• Cost: £780 for complete loft design

Project 3: Two-story extension

• Engineer fee: £1,350
• Deliverables: Full structural package, foundation design
• Multiple consultations
• Ongoing site support
• Cost: £1,350 for complete extension structure

Conclusion

Structural engineer fees for RSJ calculations typically range £350-900 for domestic projects in 2026, with most simple knockthroughs costing £400-550.

What you get:

• Professional calculations
• Compliant design
• Building Control approval support
• Legal protection
• Peace of mind

Best value approaches:

1. Get 2-3 quotes (compare scope not just price)
2. Check qualifications (Chartered essential)
3. Provide clear brief
4. Choose mid-range quote with best credentials
5. Build relationship for future projects

False economy: Skipping engineer or hiring cheapest unqualified person risks:

• Building Control rejection (wasted time/money)
• Structural failure (safety + £10k+ remedial)
• Legal prosecution
• Property sale problems

£400-550 is approximately 10-15% of total knockthrough project cost but enables the remaining 85-90% to proceed legally and safely.

Always hire chartered structural engineer (CEng, MIStructE/MICE) - non-negotiable for safe, legal, valuable RSJ installation.

Disclaimer: Fees quoted are typical 2026 UK ranges and vary by location, complexity, and engineer. Always obtain formal quotations for your specific project.