Reconfiguring an extension

Question

Hi, I am in the process of buying a house.
The house has been extended, and there is a wall running through vertically through this extension (towards back of house). 
We are looking to knock out the majority of this wall (imagining need structural engineer, potentially beam installed) 
We would then be looking at adding in two small rooms (a downstairs small WC and small utility) and add a new kitchen into this. 

On top of this we will likely need to replace flooring.
Given the reconfiguration I also could assume we would need to work with an electrician to ensure we have new sockets in the right places etc. 

The two rooms to knock through into each other are approx 7.5m x 3.4m & 5.8m x 2.2m 

Has anyone encountered similar jobs and know a rough ballpark on what I can expect cost wise & anything I haven’t considered? 

Thanks in advance

Colin · Answer

Any builder who quotes will have an electrician available to put new fixings where needed. Your main work is in putting in the steel and opening up the room. Once this done your electrics can be placed and outlets for wc then all making good done before fit out of rooms.

Jon · Answer

Depends what length the steel is if it’s hidden or s bulk head so many scenarios get a builder to look properly and he will give you a budget price

Doug · Answer

Cost wise around £6 to £8k it would all depend on what the structural engineer is saying and what the requirements are

Stephen James · Answer

You are correct this sort of work will require structural engineers calculations. The average cost of removing a wall and installing R.S.J,s is around £3,000.00. including plaster finish, you will also need building regulations to get it passed from the local authorities. You will also need plumbing work for the WC and utility room and waste connected into the drainage.
A ball park figure could be anything from £8,000.00 to £20.000.00.
Kind regards Colin from First Call Construction.

Nicholas · Answer

Your project involves significant work, and costs can vary based on location, materials, and the scope of the changes. Here’s a breakdown of what to expect and additional considerations:

Estimated Costs:
	1.	Structural Work (Wall Removal)
	•	Structural engineer report: £300–£700
	•	Steel beam installation: £1,500–£3,000 (depending on the span and complexity)
	2.	Room Reconfiguration (WC & Utility)
	•	Building walls, plumbing, and fixtures for WC & utility: £3,000–£6,000
	•	Ventilation (e.g., extractor fans): £300–£600
	3.	Kitchen Installation
	•	New kitchen units, appliances, and fitting: £7,000–£20,000+ depending on quality.
	4.	Flooring Replacement
	•	Cost depends on material:
	•	Laminate: £20–£40/m²
	•	Hardwood: £50–£100/m²
	•	Including labor: £2,000–£5,000 for the area.
	5.	Electrical Work
	•	Adding sockets, lighting, and rewiring where needed: £1,500–£3,000
	6.	Other Costs
	•	Plastering and decorating: £1,000–£2,500
	•	Waste removal and skip hire: £300–£600
	•	Building control fees: £300–£600

Total Ballpark:

Expect costs to range from £20,000–£40,000, depending on finishes, materials, and location.

Additional Considerations:
	•	Building Regulations: Ensure all work complies with building regulations, especially structural changes, plumbing, and electrical work.
	•	Drainage Adjustments: Adding a WC and utility may require changes to drainage, which can add to costs.
	•	Insulation and Heating: If the extension isn’t well insulated, you may need additional work to ensure comfort and energy efficiency.
	•	Project Management: Hiring a builder or project manager to coordinate trades may save time and reduce errors.

Consult experienced builders and get multiple quotes to refine the estimate.

Lee · Answer

Good Afternoon,

I would suggest getting a qualified builder to have a look before appointing a Structural Engineer as they should be able to tell you if it is a supporting wall or not. Worst case you should allow £700-£950 for the Structural Engineer and £1250-£1500 for the removal (including removal of the waste).

Putting new walls, plastering including making good the existing £3000-£4500

Electrics - are subject to the existing including the fuse board so more difficult to predict however £1000-£2000 should cover the cost providing you do not need a new fuse board.

Plumbing/WC - This will depend on how you can connect to the mains for the waste and where the hot/cold water will come from. This is likely to be minimum £3000 to a maximum £6000 including digging out and laying new waste pipes.

All in all, I would think you will need to spend £10,000-£15,000.

I hope this helps.

James · Answer

Even though it is a large extension, if it is a single storey it is likely that central wall is not load bearing. Typically we would just build the shell in brickwork, then put the roof joists on, then form any rooms within this shell with stud work.  It is possible the builder formed the roof joists over the stud in which case this wall would need to be replaced with a steel anyway. The biggest factor in your build will be the distance to the drains for your proposed w/c.  It sounds like top end £10k for the building works, as long as you don't propose anything too fancy in the utility.

Simon · Answer

Hi 
Would need to view works to give you a ball park figure, happy to do so , advise and quote would be free of charge, if interested contact me 
Simon

Chris · Answer

Yes structual engineer required to calculate steel sizes then refurbishment electrics plumbing  plastering decorating flooring etc on this size project estimate 22000 pounds depending cost of kitchen when you hv bought property would be more than happy to give you a free no obligation quote hope thus is useful kind regards Chris leading builders

Jeevan · Answer

Your project involves structural alterations, new room additions, kitchen installation, and flooring/electrical work. Based on similar projects, here’s a rough cost estimate:

Estimated Costs Breakdown:
Wall Removal & Structural Work (£3,500 - £7,500)
Structural engineer assessment: £500 - £1,500
Steel beam supply & installation: £2,500 - £6,000
Making good (plastering, finishing, etc.): £500 - £1,000
New Downstairs WC (£3,500 - £6,500)
Plumbing (new water supply & drainage): £1,500 - £3,000
Toilet, sink, tiling & installation: £2,000 - £3,500
New Small Utility Room (£3,000 - £6,000)
Plumbing for washing machine/dryer: £1,000 - £2,500
Cupboards/worktop/sink (if needed): £1,500 - £3,000
Ventilation if required: £500 - £1,000
New Kitchen Installation (£8,000 - £20,000+)
Basic kitchen: £8,000 - £12,000
Mid-range kitchen: £12,000 - £18,000
High-end kitchen: £18,000 - £25,000+
Plumbing & new layout configuration: £1,500 - £4,000
Flooring (£3,000 - £6,000)
Costs vary based on materials (laminate, tile, engineered wood).
Floor preparation & underfloor heating (if required) can add £1,500+.
Electrical Work (£2,500 - £6,000)
New sockets, lighting, wiring changes.
Upgrading fuse box (if required) can add £1,500 - £3,000.
Total Estimated Cost:
🔹 Low-end (basic finish): £25,000 - £35,000
🔹 Mid-range (standard finish): £35,000 - £50,000
🔹 High-end (premium materials & design): £50,000+

Other Things to Consider:
Building Regulations & Planning – You may need approval, especially for structural changes & plumbing.
Structural Engineer & Building Control Fees – Approx £1,000 - £2,500.
Temporary Accommodation – If work disrupts daily life, consider rental costs.
Hidden Issues – Older homes may have surprises (asbestos, outdated wiring, etc.).

Reconfiguring an extension

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