Do You Need Planning Permission for RSJ Beam Installation? UK Guide 2026
Installing an RSJ beam raises two separate regulatory questions: Planning Permission and Building Regulations approval. Many homeowners confuse these or assume one covers the other. This comprehensive guide clarifies what approvals you need, when they’re required, costs, and the application process for RSJ installations in 2026 UK.
Planning vs. Building Regulations
Two SEPARATE requirements:
Planning Permission
Controls: External appearance, use of land, impact on neighbors Administered by: Local Planning Authority (Council Planning Department) Question: “May I do this work?”
Building Regulations
Controls: Structural safety, fire safety, energy efficiency, accessibility Administered by: Local Building Control OR Approved Inspector Question: “Is this work safe and compliant?”
Critical: You might need BOTH, ONE, or NEITHER depending on the work!
Planning Permission for RSJ Installation
Short answer: Usually NOT required for internal RSJ installation
When Planning Permission NOT Needed
Internal alterations:
- Internal wall removal (knockthrough)
- Internal beam installation
- Loft conversion (below permitted development limits)
- No external changes
Permitted development (if within limits):
- Single-story rear extensions (<4m depth, pitched roof <4m high)
- Loft conversions (<40/50 m³ added volume, no dormer on front)
- Garage conversions (no external changes)
Examples NOT needing planning:
- 4m knockthrough combining living rooms
- RSJ header for internal doorway
- Loft conversion with rear dormers (within size limits)
- Garage conversion with RSJ header (no change to door opening)
When Planning Permission IS Needed
External appearance changes:
- Front elevation alterations (new/enlarged windows, doors)
- Hip-to-gable loft conversion
- Dormer on front roof slope (or over-sized rear dormer)
- Extending beyond permitted development limits
Examples NEEDING planning:
- 6m wide bi-fold doors on front of house
- Creating new window on side elevation (if facing highway)
- Large dormer exceeding 50% of rear roof slope
Listed buildings:
- ANY alteration requires Listed Building Consent
- Even purely internal work
- Separate from planning permission
- More stringent approval process
Conservation areas:
- Stricter rules than regular permitted development
- Often require planning for work that would normally be permitted
- Check with local authority
Article 4 Direction areas:
- Some areas have removed permitted development rights
- Work requiring planning even if normally permitted
- Common in historic districts, areas of special character
How to Check
Step 1: Contact Local Planning Authority
- Phone planning department
- Describe proposed work
- Ask if planning required
Step 2: Submit Planning Permission if Required
- Application fee: £206 (householder application, 2026)
- Drawings required (site plan, elevations, floor plans)
- Processing time: 8 weeks
- May be approved, approved with conditions, or refused
Step 3: Appeals Process
- If refused, can appeal
- Or modify proposal and reapply
- Appeals take 3-6 months
Building Regulations for RSJ (ALWAYS Required!)
Clear answer: YES, Building Regulations approval MANDATORY for ALL RSJ installations
Why Always Required
RSJ installation is “building work” and specifically:
- Structural alteration (Part A)
- Affects structural stability -Must comply with Building Regulations requirements
No exceptions: Even small internal beam installations require approval
Building Regulations Application Process
Two routes available:
Route 1: Local Authority Building Control
- Apply to council Building Control department
- Inspectors visit site
- Fee: £220-650 depending on project value/complexity (2026 rates)
- Standard option
Route 2: Approved Inspector
- Private Building Control companies
- May be faster/more flexible
- Competitive fees
- Same legal standing as council
What You Need to Submit
Full Plans Application (recommended for structural work):
Documents required:
- Application form (council provides)
- Site location plan (1:1250 scale)
- Floor plans showing:
- Existing layout
- Proposed layout
- Beam location
- Dimensions
- Structural engineer’s calculations and drawings:
- Beam specification
- Load calculations
- Support details (padstones, etc.)
- Connection details
- Method statement (how work will be done)
Fee examples (2026):
- Simple knockthrough: £220-350
- Loft conversion: £400-600
- Extension with multiple beams: £500-800
Processing time:
- Council reviews: 5 weeks (can extend to 8 weeks)
- Approval or rejection issued
- Conditional approval possible (further info needed)
Building Notice (alternative, not recommended for RSJ work):
- Simpler application
- Work can start sooner
- BUT no approved plans (riskier)
- If non-compliant discovered, must rectify
Inspection Schedule
Building Control will inspect:
Before work starts:
- Review temporary support arrangements
- May inspect props in place
During installation:
- After padstones installed, before beam placed
- After beam installed, before making good above
After completion:
- Final inspection before removing temporary support
- Check fire protection if required
- Verify compliance
Completion Certificate issued when all satisfactory
Penalties for Not Obtaining Approval
If you proceed without Building Regs approval:
Immediate consequences:
- Building Control can issue enforcement notice
- Work must stop immediately
- May require opening up for inspection
Long-term consequences:
- Property sale problems (solicitors check compliance)
- Mortgage issues (lenders require certificates)
- Insurance invalidation (claims rejected)
- Reduced property value
Regularisation:
- Can apply retrospectively (more expensive, often £800-1,500+)
- May require destructive inspection (opening up walls)
- May refuse if can’t verify compliance
- If refused: Remove work and rebuild properly!
Criminal prosecution possible:
- Fines up to £5,000
- PLUS daily fines if work continues after notice
NEVER worth the risk - ALWAYS obtain approval!
Complete checklist
For typical internal knockthrough (4m opening, bedroom above):
Planning Permission
- Checked if conservation area/listed building → If NO, planning likely not needed
- Confirmed no external changes → If NO external changes, planning not needed
- If required: Submit application (£206, 8 weeks)
Building Regulations (ALWAYS)
- Engage structural engineer (£350-600)
- Engineer produces calculations and drawings
- Submit full plans application to Building Control (£220-400)
- Await approval (5-8 weeks)
- Notify Building Control 24-48hrs before starting
- Book inspections (before/during/after)
- Complete work per approved plans
- Final inspection and completion certificate
Total timeline: 8-12 weeks from engineer engagement to completion certificate
Specific Scenarios
Scenario 1: Simple Internal Knockthrough
Work: Remove internal wall, install 203×133×30 RSJ, 4m span
Planning: NOT required (internal work) Building Regs: REQUIRED Cost: Engineer £380, Building Control £280 = £660 approvals Timeline: 6-10 weeks
Scenario 2: Loft Conversion with Ridge Beam
Work: Ridge beam replacement, floor strengthening, 2 Velux windows (rear)
Planning: Check permitted development limits
- If within limits (volume, height restrictions): NOT required
- If exceeds: REQUIRED
Building Regs: REQUIRED (structural + fire safety) Cost: Engineer £600-900, Building Control £450-650, Planning if needed £206 Timeline: 10-16 weeks
Scenario 3: Garage Conversion
Work: RSJ header over garage door opening (keeping opening same size), internal conversion to room
Planning: Usually NOT required if:
- No external appearance change
- No increase in property footprint
Building Regs: REQUIRED (structural, fire, thermal, ventilation) Cost: Engineer £400-650, Building Control £350-550 Timeline: 8-12 weeks
Scenario 4: Kitchen Extension (Single Story Rear)
Work: 3m deep × 4m wide extension, RSJ beam at connection to house
Planning:
- If <4m deep (detached) or <3m (terraced/semi): Permitted development, NOT required
- If exceeds: REQUIRED
Building Regs: REQUIRED (full submission for extension) Cost: Architect/designer £800-1,500, Engineer £500-800, Building Control £500-750, Planning if needed £206 Timeline: 12-20 weeks
Scenario 5: Listed Building Internal Beam
Work: Any RSJ installation in listed building
Planning: Listed Building Consent REQUIRED (even internal work) Building Regs: REQUIRED Cost: Heritage consultant £400-1,000+, Engineer £500-900, Building Control £400-700, Listed Building Consent £206 Timeline: 16-26 weeks (heritage approval slow)
Special considerations: May have to use traditional materials/methods, modern steel beams sometimes refused
Common Mistakes
Mistake 1: Assuming Building Regs not needed “It’s only internal, no one will know” Reality: Solicitors check during sale, Building Control can prosecute Fix: ALWAYS obtain Building Regs approval
Mistake 2: Confusing Planning and Building Regs “I don’t need planning so I don’t need any approval” Reality: Building Regs separate, ALWAYS required for structural work Fix: Understand they’re two different things
Mistake 3: Starting work before approval “I’ll apply while work progresses to save time” Reality: Illegal, work must stop, potential prosecution Fix: Apply BEFORE starting, wait for approval
Mistake 4: DIY application without engineer “I’ll submit plans myself to save money” Reality: Building Control will reject without structural engineer calculations Fix: ALWAYS engage structural engineer for RSJ work
Mistake 5: Not booking inspections “I’ll call when finished” Reality: Must inspect at specific stages, can’t verify compliance retrospectively Fix: Book inspections at required stages, don’t conceal work before inspection
Costs Summary
Typical knockthrough project (4m beam):
| Item | Cost |
|---|---|
| Structural engineer | £350-600 |
| Building Control fee | £220-400 |
| Planning (if required) | £206 |
| Total approvals | £570-1,206 |
These costs are NON-OPTIONAL for safe, legal, sellable work
False economy: Skipping approvals risks £5,000+ fines, £10,000+ remedial work, property sale failure
Conclusion
Planning Permission for RSJ installation:
- Usually NOT required for internal work
- MAY be required if external changes or extensions
- Check with Local Planning Authority
Building Regulations for RSJ:
- ALWAYS required
- No exceptions
- Structural engineer essential
- Multiple inspections
- Completion certificate critical
Process summary:
- Engage structural engineer
- Check if planning required (usually not for internal)
- Submit Building Regulations application (always)
- Await approvals
- Start work only after approval
- Arrange inspections
- Obtain completion certificate
- File safely for future
Budget £570-1,200 for professional fees and approvals - this is mandatory cost of legal, safe structural work.
Never proceed without approvals - consequences far exceed cost of compliance!
Disclaimer: Regulations vary by location and specific circumstances. Always check with your Local Planning Authority and Building Control for project-specific requirements. This guide provides general UK information for 2026.
