The cost of a house extension in Birmingham varies based on size, shape, and quality of finishes. Based on recent projects, we’ve provided an up-to-date guide to help you estimate your budget. The most common type of extension in Birmingham is a single-storey rear extension measuring 4.0 meters deep by 5.0 meters wide (20 square meters) with a sloping tiled (lean-to) roof.
Essential Services Costs
| Service | Price |
|---|---|
| Architect or Home Designer Plans | £850 – £1,500 |
| Planning and Building Control Applications | £800 – £1,050 |
| Building Shell (Water Tight & Plastered) | £22,500 – £25,000 |
| Basic Glazing (PVCu Door & Window) | £1,500 – £2,000 |
| Heating and Electrical | £2,000 – £3,000 |
| Decoration (Paint) | £1,500 |
| Flooring (Laminate/Carpet) | £500 |
| Total | £28,250 – £34,550 |
Additional Costs for Knock-Through into Existing Rooms
| Service | Price |
| Structural Engineer Beam Design | £300 – £700 |
| Steel Beam Installation | £2,000 – £3,500 |
| Making Good Existing Floors, Walls, and Ceilings | £3,000 – £4,000 |
| Roof Lights | £750 per unit |
| Aluminium Bi-Fold Doors (4 Meters) | £4,000 – £5,000 |
| Toilet | £3,000 – £4,500 |
| Kitchen Extension | £8,000 – £15,000 |
| Heating and Electrical (Additional) | £500 – £1,000 |
| Decoration (Additional) | £750 – £1,250 |
| Total | £23,250 – £35,700 |
Grand Total with Knock-Through, Kitchen, and Toilet
| Total | £51,500 – £70,250 | | Cost per Additional Square Meter | £1,750 per m² |
Potential Unknown Costs
Some unexpected costs may arise, including:
- Sewer build overs
- Party wall agreements
- Asbestos removal
- Utility installation
- Boiler upgrades
- Electrical fuseboard/wiring upgrades
- Moving meters
- Listed building consent
These factors should be identified by your architect or experienced architectural designer before approaching a builder.
Further Information
Architectural Plans
Architectural plans are essential for determining feasibility, legal planning approvals, and building control compliance. They also serve as a reference for builders.
Planning and Building Control Applications
Planning applications come with fees, and while some extensions fall under permitted development, it’s advisable to confirm this in writing with Birmingham City Council to avoid legal complications when selling your home.
Building the Shell
This includes foundations, drainage excavation, concrete works, insulated cavity brickwork, and a tiled roof. The work is typically completed up to a plastered finish, marking the transition from messy construction to interior finishing.
Glazing
Glazing options range from basic PVCu windows and doors to premium aluminium bi-fold or slimline sliding doors. The latter offer better aesthetics and improved glass-to-wall ratios but come at a higher cost.
Heating & Electrical
Basic costs assume an extension of the existing heating system, adding one or two radiators and installing 6-8 spotlights, switches, and sockets. Costs rise significantly for kitchen extensions or upgrades to existing wiring, boilers, and fuseboards.
Decoration & Flooring
Costs depend on material choices. Basic laminate or carpet starts at £500, while premium finishes like Karndean or engineered wood can increase costs to £2,500 or more.
Knock-Through and Kitchen Extensions
Knock-Through Costs
Removing structural walls for open-plan living requires structural engineering calculations and approvals. This work often causes significant disruption and may necessitate additional updates to maintain a seamless flow between old and new spaces.
Kitchen Extensions
Kitchens are a major cost factor. Depending on location and layout, additional drainage and plumbing work may be necessary.
We hope this guide provides clarity on the costs of extending your home in Birmingham. If you’re looking to move forward with your project, feel free to get in touch!
