Even if you don’t need planning permission, you almost certainly need Building Regulations approval. This is where many DIY-project extensions go wrong. Here is a plain-English guide to what Building Regs require for extensions in the West Midlands in 2026.
Planning permission versus Building Regulations
These are two separate approvals with two separate submissions. Planning covers what you can build (size, appearance, impact on neighbours). Building Regs cover how it is built (structural stability, thermal performance, fire safety, drainage, ventilation).
The main Building Regs approved documents that apply to extensions
Part A: Structure
Foundations, load paths, structural openings, retaining walls. Any load-bearing changes need structural calculations by a chartered engineer.
Part B: Fire safety
Escape routes, fire spread between properties, smoke detection. If you’re extending near a boundary, the wall may need to be fire-rated.
Part C: Site preparation and moisture
Damp-proof courses, damp-proof membranes, drainage away from the property. Basement conversions have very strict Part C requirements.
Part F: Ventilation
Every room needs specified levels of ventilation. Kitchens and bathrooms need mechanical extract. Modern builds often benefit from MVHR (Mechanical Ventilation with Heat Recovery).
Part L: Conservation of fuel and power
This is the big one. Sets minimum U-values for walls, roofs, floors, windows. Also requires SAP (Standard Assessment Procedure) calculations for extensions.
Part M: Access
Requirements for accessibility including door widths, thresholds and turning circles. Applies to certain extension types.
Part P: Electrical safety
All electrical work must be certified to 18th Edition standards by a competent electrician (NICEIC/NAPIT registered).
Minimum U-values for extensions in 2026
- External walls: 0.18 W/m²K (typically 100mm PIR board equivalent)
- Roof: 0.15 W/m²K
- Floor: 0.18 W/m²K
- Windows: 1.4 W/m²K (double glazed with argon fill)
- Doors: 1.4 W/m²K
These are current requirements. If you’re planning ahead for the 2027 Future Homes Standard, aim lower on all counts.
How the Building Regs process works
Option 1: Full Plans application
You submit full construction drawings to your local authority (Redditch Borough Council, Birmingham City Council etc.). They approve or ask for changes before you build.
Option 2: Building Notice
You give notice and start building. An inspector visits at key stages. Higher risk if something is wrong — you may have to rip it out.
Option 3: Approved Inspector (private)
A private Approved Inspector (rather than the council) certifies the build. Often faster and more responsive than council BCOs. We use approved inspectors on most of our extension projects.
Inspection stages
- Commencement of work
- Foundations excavated
- Foundations poured (before backfill)
- DPC and oversite
- Drains before covering
- Roof structure
- Insulation
- Completion
Missing an inspection means the inspector cannot certify what is behind the wall — and that means no completion certificate, which affects sale of the property forever.
The completion certificate is worth having
When you eventually sell, buyers’ solicitors ask for Building Regs completion certificates on any work done. No certificate = potential price reduction or sale falling through. Doing the job properly is not optional.
How CK Construction handles Building Regs
Every project we deliver includes full Building Regs application and management. We appoint the inspector, schedule all inspections, and hand you the completion certificate on handover. It’s built into our fixed-price quote — no surprises.
Free advice on your extension
We cover Redditch, Birmingham, Solihull and Warwickshire. Call 01527 521835 for a free chat about your project.
Serving homeowners across West Midlands, Worcestershire, Warwickshire, Gloucestershire and the wider region.