Has anyone added a second storey to their extension

Question

Roughly, how much would building a second floor on top of an existing extension cost? It's about 4 metres by 6 metres

Gary · Accepted Answer

Yes you can add to existing extension depending on a report from an inspection.price roughly around £2.300 per m2

Cliff · Answer

you will have to get calculations to see if the original footings are sufficient for adding extra loadings you may consider using a light Weight  construction ie timber

Josh · Answer

Hi Jenny ,

At a rough guide it would be around £2500 per m2

Thanks

Tony · Answer

You might need the foundations exposed to establish if they are sufficient for the second floor. The rough cost for the extension would be around £72,000 plus VAT. It will depend on what needs to be rearranged inside to enable the extension to work.

Tomasz · Answer

It is depend of actual footings and requirements for double storey. Price is also depend of the finishing, numbers of windows, type of the roof etc. Also what area you are? I would say £50-60k.

Spencer · Answer

Sometimes it’s feasible; especially if it’s from a garage off an end gable wall. In any event you’ll need to excavate two or more areas to check the ground bearing strata- depth and thickness of the original escarpment needs to be suitable and if it isn’t you’ll need to underpin.

I’d next consider the state of the existing masonry and ascertain if I can get a nice brick match. If the original brickwork is tatty, aged or not of a neat appearance it’ll look awful when you build need courses atop of it. - if this is the case alongside underpinning then I usually advise to start from scratch.

Without knowing more about the intended project, it’s difficult to gauge the cost, but I costed a two storey of this nature with the downstairs as a garage and the upstairs as a bedroom with en-suite just recently and the build to completion was £78k.

Martynas · Answer

Structure & shell (walls, roof, steels, floor): ~£19k

Scaffolding & access: ~£3k

Roof removal & temporary works: ~£2.5k

Windows & doors: ~£3k

Plastering, insulation & finishes: ~£8k

Electrics & heating: ~£6k

Joinery, decoration & cleanup: ~£6.5k

Build total (ex VAT): ~£48k
With 20% VAT: ~£57.5k

Josh · Answer

Hi 

Based on the measurements you’ve given me (4m × 6m, around 24m²), a rough guide price for adding a second floor above the existing extension would be in the region of £40,000–£60,000.

This estimate is worked out using typical build costs of £1,650–£2,500 per m² and would cover the main structure, brick/block work, roof tie-in, windows/doors, and basic internal works.

Please note this is only a ballpark figure as I haven’t seen the job in person. The final cost could vary depending on the existing foundations, access, materials, and the level of finish.

Oleh · Answer

Hi! 👋

Yes, people do add a second storey on top of an existing extension, but the cost really depends on the structure you already have. The foundations and walls need to be strong enough to take the extra load, so a structural engineer’s input is essential before you start.

As a very rough guide, building costs in the UK are usually somewhere between £1,800–£2,500 per m² for a standard finish. For a 4 m × 6 m extension (about 24 m²), that works out to around £45,000–£60,000. If you want higher-end finishes or there are structural complications, it could push closer to £70k+.

On top of that you’ll also need to budget for:
	•	Architect and structural engineer fees
	•	Planning permission and building control sign-off
	•	Party wall agreements (if you’re attached)
	•	Internal fit-out like bathroom/kitchen if you’re adding them

So realistically, most people allow at least £50k+ for something this size. Getting a couple of builders out for quotes (and confirming with building control) will give you a much clearer picture.

Benjamin · Answer

depending on the structure and whether the existing foundations meet building requirements to take the load bearing of another storey structural survey and a test hole will have to be carried to to con from this.
 cost wise what type of roof detail, internal works required i.e. bathrooms windows, knocking out openings etc will affect the costs but. you can base it at £1600 to £1800 per square meter so for 24m2 area guideline costs will be £ 38400 to £43200. hop this helps. kind regards

Has anyone added a second storey to their extension

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